M A S S A C H U S E T T S I N S T I T U T E O F T E C H N O L O G Y

Laboratory for Nuclear Science Report

Report Number 107 Aprii 1980

T H E F I R S T Y E A R O F M A R K - J :P h y s i c s W i t h H i g h E n e r g y E l e c t r o n -

P o s i t r o n C o l l i d i n g B e a m s

M S B

by the Mark-J Collaboration

(the AACHEN, DESY, M.I.T. NIKHEF, PEKING Collaboration)

D .P . Barber , U. Becker , H. Benda, A. B8hm, J .G . Branson , J . Bron, D. Buikman

J .D . Burger , C.C. Chang, H.S. Chen, M. Chen, C.P. Cheng, Y.S. Chu, R. C l a r e ,

P. Duinker, G.Y. Fang, H. F e s e f e l d t , D. Fong, M. Fukushima, J .C . Guo,

A. H a r i r i , G. H er ten , M.C. Ho, H.K. Hsu, R.W. K a d t l , W. Krenz, J . L i ,

Q.Z. LI , M. Lu, D. Luckey, C.M. Ma, D.A. Ha, G.G.G. M assa ro , T. Matsuda ,

H. Newman, M. Pohl , F .P . Poschmann, J . P . Revol , M. Rohila, H. Rykaczewski,

K. Sinram, H.W. Tang, L.G. Tang, Samuel C.C. Ting , K.L. Tung, F. Vannucci ,

X.R. Wang, P .S . Wei, M. Whi te , G.H. Wu, T.W. Wu, J . P . X i , P .C. Yang, C.C. Yu

X.H. Yu, N.L. Zhang and R.Y. Zhu.

I I I . P h y s i k a l l s c h e s I n s t i t u t T echn ische Hochschule , Aachen, West Germany.

Deu tsches E le k t ro n e n -S y n c h ro t ro n ( D . E . S . Y . ) , Hamburg, West Germany.

L abora to ry f o r Nuclear S c i e n c e , M a s s a c h u s e t t s I n s t i t u t e o f Technology,

Cambridge, M a s s a c h u s e t t s , U.S.A.

N a t i o n a a l I n s t l t u u t voor K e r n f y s i c a en H o g e - E n e r g l e f y s i c a , {NIKHEF),

S e c t i e H, Amsterdam, The N e t h e r l a n d s .

I n s t i t u t e of High Energy P h y s i c s , Chinese Academy o f S c i e n c e , Pek ing ,

P e o p l e ’ s Republic o f China.

This i s t h e complete e d i t i o n o f the p r e l i m i n a r y v e r s i o n p r e p a r e d i n 1979,

DISCLAIMER

- 2 -

Table of Contents

ABSTRACT

1) INTRODUCTION

2) EXPERIENCE AT PETRA

3) THE MARK J EXPERIMENT

3.1 P hys ics O b je c t iv e s

3 .2 The D e te c to r

a) Overview

b) Luminos ity Monitor

c) D r i f t Chambers

d) T r ig g e r

e) D e te c to r C a l i b r a t i o n

f ) Online Data C o l l e c t i o n and Data M o n i to r in g

3 .3 O f f l i n e A n a ly s i s

a) D i r e c t i o n and Energy Measurements

b) O f f l i n e Data Reduct ion

c) Monte Car lo S im u la t ion

d) R a d i a t i v e C o r r e c t io n s f o r Lum inos i ty M o n i to r in g and T e s t s of QED

4) PHYSICS RESULTS

4 . 1 T e s t s of QED and of U n i v e r s a l i t y o f Charged Leptons

a) Bhabha S c a t t e r i n g

b) Muon and Tau P a i r P ro d u c t io n

4 . 2 Hadronlc F i n a l S t a t e s

a) Hadron I d e n t i f i c a t i o n

b) T o t a l Hadronic Cross S e c t io n

4 .3 J e t A n a ly s i s

a) T h ru s t D i s t r i b u t i o n s

b) J e t A n a ly s i s Using Fo:t-Wolfram Moments

c) A Study of I n c l u s i v e Muons in Hadronic Events

d) D iscove ry of 3 - J e t Events

e) D e te r m in a t io n of t h e S trong Coupling C ons tan t

4 .4 Comparison w i th o t h e r Exper iments a t PETRA

5) CONCLUSION

ACKNOWLEDGEMENTS

Abstract

This r e p o r t rev iews th e e x p e r i m e n t a l i n v e s t i g a t i o n of h igh

+ -energy e e i n t e r a c t i o n s by th e HARK J c o l l a b o r a t i o n a t PETRA, th e

e l e c t r o n - p o s i t r o n c o l l i d i n g beam a c c e l e r a t o r a t DESY i n Hamburg, West

Germany. The p h y s i c s o b j e c t i v e s i n c lu d e s t u d i e s of s e v e r a l p u r e l y

e l e c t r o m a g n e t i c p ro c e s s e s and h a d r o n i c f i n a l s t a t e s , which f u r t h e r

our knowledge of the n a t u r e of t h e fundamenta l c o n s t i t u e n t s and of t h e i r

s t r o n g , e l e c t r o m a g n e t i c and weak i n t e r a c t i o n s . B e fo re d i s c u s s i n g th e

p h y s i c s r e s u l t s , the main f e a t u r e s and the p r i n c i p a l components of th e

MARK J d e t e c t o r a r e d i s c u s s e d i n te rm s of d e s i g n , f u n c t i o n , and pe r fo rm ­

ance . S e v e ra l a s p e c t s of t h e o n l i n e d a t a c o l l e c t i o n and t h e o f f l i n e

a n a l y s i s a r e a l s o o u t l i n e d . R e s u l t s a r e p r e s e n t e d on t e s t s of quantum

— 4'— ■+'*~ 4*e l e c t ro d y n a m ic s u s in g e e + e e , p ij and t t ~ , on the measurement of

R, the r a t i o of t h e had ro n ic to t h e p o i n t - l i k e muon p a i r c r o s s s e c t i o n ,

on the s e a r c h f o r new quark f l a v o r s , on the d i s c o v e r y of t h r e e j e t e v e n t s

a r i s i n g from the r a d i a t i o n of hard n o n c o l l i n e a r g lu o n s a s p r e d i c t e d by

quantum chromodynamics,and on th e d e t e r m i n a t i o n of th e s t r o n g c o u p l in g

c o n s t a n t a .s

This a r t i c l e r ev iew s the e x p e r i m e n t a l program of t h e MARK J

c o l l a b o r a t i o n us ing PETRA a t DESY in Hamburg, West Germany. PETRA ir>

the w o r ld ’ s h i g h e s t energy e l e c t r o n - p o s i t r o n c o l l i d i n g beam s t o r a g e

r i n g now in o p e r a t i o n . There have been fo u r groups (JADE. MARK-J, PT.UTO

and TASSO) u s in g PETRA s i n c e 1979. The i r r e s u l t s a r e s u p p o r t i v e ar;-.l

complementary t o each o t h e r .

E l e c t r o n - p o s i t r o n c o l l i s i o n s p ro v id e a p a r t i c u l a r l y c l e a n wt'y

to s tudy th e n a t u r e of t h e fundamenta l c o n s t i t u e n t s of m a t t e r and t h e i r

i n t e r a c t i o n s because of t h e p o i n t - l i k e n a t u r e of l e p t o n s . Exper iments

a t PETRA a r e thus f r e e of t h e c o m p l ic a t io n s t h a t a r i s e in s t u d i e s of

had ron -had ron or l e p to n - h a d r o n c o l l i s i o n s , where th e hadrons themse lves

have a complex i n t e r n a l s t r u c t u r e which must be unders tood in d e t a i l2

b e fo re new in f o r m a t io n on the l a r g e q i n t e r a c t i o n s of t h e c o n s t i t u e n t s

can be e x t r a c t e d .

The MARK J d e t e c t o r was proposed d u r in g th e s p r i n g of 1976, Tho

d e t e c t o r employs c a l o r i m e t r y to measure h a d ro n ic and e lec t rom agne t ic

energy f low. L a r g e - a r e a a r r a y s of d r i f t chambers t o g e t h e r w i th the l a rg e

magne tized i r o n t o r o i d s which form the main body of the d e t e c t o r d i s t i n ­

gu is h hadrons from muons and de te rm ine the muon momenta. A compact

i n n e r d e t e c t o r i s used to measure th e v e r t e x and the d i r e c t i o n s of

charged t r a c k s . The ma jor components of th e d e t e c t o r a re c o n s t r u c t e d

u s in g s im ple te c h n o lo g y , so t h a t the a p p a r a tu s has o p e ra t e d w i th n e g l i g i b l e

down-time.

The r e l a t i v e s i m p l i c i t y of the d e t e c t o r made p o s s i b l e the

i n s t a l l a t i o n o f the major p a r t o f the d > t e c t o r , as w e l l as the a s s o c i a t e d

e l e c t r o n i c s and d a t a a c q u i s i t i o n hardware , over a p e r io d of on ly s i x

months from May-October 1978. The MARK J was th us ready f o r d a t a - t a k i n g

a t c.he s t a r t o f p h y s i c s r u n s a t PETRA i n O c tober , iS /B and i t s f i r s t

-5-

1) INTRODUCTION

p r e l i m i n a r y p h y s ic s r e s u l t s were p r e s e n t e d ? t DESY by the end of 1978.

PETRA has run w i th beam e n e r g i e s r a n g in g from 6 to 16 GeV,

and th e MARK J has c o l l e c t e d more than 90% of the t i m e - i n t e g r a t e d

-1lu m in o s i ty made a v a i l a b l e d u r in g p h y s ic s r u n s , a t o t a l of 3-5 pb

The h igh deg ree of o p e r a t i n g e f f i c i e n c y i s due to the r e l a t i v e i n s e n s i t i v i t y

of the i n n e r shower c o u n te r and c a l o r i m e t e r e lem en ts to s y n c h r o t r o n

r a d i a t i o n and o t h e r low energy background. This has led to a low t r i g g e r

r a t e , and minimal dead time d u r in g d a t a t a k i n g .

The g e n e r a l f e a t u r e s of t h e PETRA machine and i t s per formance

a r e g iven in S e c t io n 2. The MARK J exper iment i s d i s c u s s e d i n S ec t io n s

3 . 1 - 3 . 3 , s t a r t i n g w i th an o v e r a l l view o f the g o a l s of the p h y s i c s program

in S e c t io n 3 . 1 . The p r i n c i p a l components of the d e t e c t o r a r e in t ro d u ced

i n S e c t io n 3 . 2 , where th e d e s ig n and f u n c t i o n of the p a r t i c l e d e t e c t o r s ,

lu m in o s i ty m o n i to r , f a s t - e l e c t r o n i c s and m i c r o p r o c e s s o r -b a s e d t r i g g e r s ,

and the o n l i n e d a t a a c q u i s i t i o n and m o n i to r in g systems a r e d i s c u s s e d .

S e c t io n 3.3 d e a l s with a s p e c t s of the o f f l i n e a n a l y s i s : the a l g o r i t h m s used

to measure energy flow in th e d e t e c t o r , the d a t a r e d u c t i o n and event

s e l e c t i o n p ro c e d u re s fo r each of s e v e r a l e+e f i n a l s t a t e s , t h e computer4* ***

s i m u l a t i o n of a v a r i e t y of e e r e a c t i o n s b o th as they a r e produced and

as they appea r in the MARK J d e t e c t o r , and th e methods used to compute the

l u m in o s i ty . S e c t io n s 4 . 1 - 4 . 3 rev iew the MARK J p h y s ic s r e s u l t s . T es te of

quantum e l e c t ro d y n a m ic s (QED) and of the u n i v e r s a l i t y of the charged

lep ton= a r e p r e s e n t e d in S e c t io n 4 . 1 . The h a d ro n ic even t s e l e c t i o n c r i t e r i a ,

t h e measurement of R, th e r a t i o of tne c r o s s s e c t i o n f o r hadron p ro d u c t io n

to t h e c r o s s s e c t i o n f o r p o i n t - l i k e muon p a i r p r o d u c t i o n , and th e use of

th e R measurement to s e a r c h f o r new quark f l a v o r s a r e d i s c u s s e d in S ec t io n

4 . 2 . S e c t i o n 4 .3 fo cu ses on j e t a n a l y s i s : t h e i n t e r p r e t a t i o n of the topo-

- 6 -

formed by the f r a g m e n ta t io n of quarks and g luons i n th e framework o f QCD.

S e v e ra l methods of c h a r a c t e r i z i n g th e o v e r a l l even t shape a r e d e s c r i b e d ,

and the methods a r e a p p l i e d to s e n s i t i v e s e a r c h e s f o r t h e top quark

c o n t r i b u t i o n to th e had ro n ic continuum. The d e t a i l e d a n a l y s i s of th e

even t topo logy which led to the d i s c o v e r y by th e MARK J of t h r e e j e t

e ven t s a r i s i n g from the r a d i a t i o n of hard n o n - c o l l i n e a r g lu o n s , and the

d e t e r m in a t io n o f t h e s t r o n g c o u p l in g c o n s t a n t oc , a r e a l s o d i s c u s s e d .sS e c t io n 5 c l o s e s th e r e p o r t w i th a summary o f th e p h y s i c s con­

c l u s i o n s .

-7-

logical. features of the evunts in terms of jets of particles which are

PETRA [!} (Positron E,lektron Tandem Ringbeschleuriiger Anlage)

ii EXPERIENCE AT PETRA

c o l l i d i n g beam machine. S ince i t s commiss ioning , PETRA beams have been

a v a i l a b l e f o r p h y s ic s runs 60% o f the t im e , w i th the rem ain ing t ime be ing

devoted to machine development and main tenance p e r io d s [ 2 ] ,

The r i n g , w i th a c i rc u m fe ren c e of 2 .3 k i l o m e t e r s , has e i g h t

long s t r a i g h t s e c t i o n s of which two a r e r e s e r v e d fo r t h e RF a c c e l e r a t i n g

c a v i t i e s . At p r e s e n t only four of th e e x p e r im e n ta l a r e a s a r e occup ied .

The remain ing two e x p e r im e n ta l a r e a s a r e r e s e r v e d fo r second g e n e r a t i o n

e x p e r i m e n t s .

*4”began o p e r a t i o n in the f a l l of 1978 as the w o r l d ' s h i g h e s t energy e e

a c aNW hA'.i Rf HALLS

//' \

P E T R A LlNACI \

SE HALL

FIGURE 1.The layout of PETRA e+e~ Storage Ring at DESY.

The o r i g i n a l i n j e c t i o n scheme u t i l i z e d b o th o f the e x i s t i n g

DESY f a c i l i t i e s , DESY and DORIS. E l e c t r o n s , i n i t i a l l y a c c e l e r a t e d in

LINAC I ( see F ig . 1) a r e i n j e c t e d i n t o DESY (D eu tsches K lek t ro n e n Syn c h r o t r o n )

where they a r e f u r t h e r a c c e l e r a t e d to 6 GeV and i n j e c t e d i n t o PETRA.

P o s i t r o n s fo l lo w a somewhat more com pl ica ted p a t h : a f t e r i n i t i a l a c c e l e r a ­

t i o n in LINAC I I , p o s i t r o n s a r e I n j e c t e d v i a DESY i n t o DORIS (Dopp e l - R l n g -

S p e i c h e r ) , where they a r e accumula ted a t an energy o f 2 .2 GeV. S to r e d

p o s i t r o n bunches i n DORIS a r e th e n t r a n s f e r r e d back t o DESY f o r f u r t h e r

a c c e l e r a t i o n to 6 GeV, the minimum PETRA i n j e c t i o n e n e rg y .

With t h e d i s c o v e ry of th e u p s i l o n ( T) r e s o n a n c e in 197 7 a t FNAL [3]

and the c o n f i r m a t i o n i n e+e i n t e r a c t i o n s [ 4 ] , t h e need to o p e r a t e DORIS as

a s t o r a g e r i n g in dependen t of PETRA was r e a l i z e d . C o n s eq u en t ly , i n the

f a l l o f 1977 th e d e c i s i o n was made t o c o n s t r u c t a P o s i t r o n I n t e n s i t y

Accumulator (PIA) [5] to f r e e DORIS f o r p h y s i c s r u n s . In t h i s new i n j e c t i o n

scheme, p o s i t r o n s a r e accumula ted i n PIA a f t e r a c c e l e r a t i o n in LINAC I I .

Twenty s u c c e s s i v e LINAC bunches a r e i n j e c t e d i n t o PIA, compressed i n phase

s pace , and t r a n s f e r r e d t o DESY f o r a c c e l e r a t i o n and i n j e c t i o n i n t o PETRA.

PIA was assembled in reco rd t ime and s i n c e th e summer of 1979 has se rved

as the i n j e c t o r f o r both DORIS and PETRA.

30 -2 -.1The av e ra g e l u m in o s i ty i s 2x10 cm s ec a t beam e n e r g i e s of

15 GeV. I t i s expec ted t h a t th e l u m i n o s i t y w i l l i n c r e a s e In t h e n e a r f u t u r e

w i th more o p e r a t i o n a l e x p e r i e n c e .

In t h e f i r s t y e a r of o p e r a t i o n , PETRA has run from an energy of

12 GeV to 31.6 GeV. I t haB run r e l i a b l y w i th v e ry l i t t l e f a i l u r e s . The

s t a b i l i t y of t h e machine was t h e majo r rea son why a l l groups a t PETRA have

been a b l e to pe r fo rm t h e i r e x p e r im e n t s s a t i s f a c t o r i l y .

3 .1 P h y s ic s O b j e c t i v e s

The MARK J d e t e c t o r [ 6 ] , which i d e n t i f i e s and measures th e ene rgy and

d i r e c t i o n o f muons, e l e c t r o n s , charged and n e u t r a l hadrons w i th c l o s e to

uni form e f f i c i e n c y and w i t h ~4tt a c c e p t a n c e , i s c a p a b le of f u l f i l l i n g a

broad range of p h y s i c s o b j e c t i v e s . Some of t h e pr ime p h y s ic s g o a l s of th e

exper im ent a r e :

1) To s tu d y th e v a r i o u s QED p r o c e s s e s shown i n F ig . 2 and t o s tudy

the u n i v e r s a l i t y of t h e known cha rge d l e p t o n s iti t h e i r e l e c t r o m a g n e t i c

i n t e r a c t i o n s . At PETRA the a v a i l a b l e c.m. e n e rg y i s / s = 32 GeV (q^ up2 1 to 1000 GeV ) . S ince f i r s t o r d e r QED p r o c e s s e s e x h i b i t a / s c r o s s

s e c t i o n dependence th e MARK J can probe th e v a l i d i t y of QED w i t h an o rde r

of magnitude g r e a t e r s e n s i t i v i t y than t h a t p r e v i o u s l y a v a i l a b l e in e a r l i e r

c o l l i d i n g beam expe r im en t s per fo rmed a t s t o r a g e r i n g s a t SLAC, DESY, ADONE

2 2and CEA in the range of q 50 GeV ,

3) THE MARK J EXPERIMENT

e + e

FIGURE 2.Electron, muon and tau pair production in lowest order.

2) To s e a r c h f o r new q u a rk f l a v o r s by s t u d y i n g th e ene rgy and a n g u la r

d i s t r i b u t i o n s o f i n c l u s i v e muon p r o d u c t i o n i n h a d r o n ic e v e n t s ( F i g u r e 3 a ) .

3) U s ing th e d i s t r i b u t i o n s o f ye and yh f i n a l s t a t e s shown i n F i g . 3 b t o

s e a r c h f o r t h e e x i s t e n c e o f new charged l e p t o n s h e a v i e r than th e t a u .

-11 -

u(q)

,v(q)

[ b)v (q)

'u(q)

FIGUREa. Diagram for production and decay of heavy quarks in e+e~ annihilation.

X _b. Diagram for production and decay of heavy leptons in e c annihilation.

4) To measure t h e t o t a l h a d ro n ic c r o s s s e c t i o n (F ig . 4) and th e re b y

th e s t r u c t u r e and ene rgy dependence, o f th e t o t a l c r o s s s e c t i o n , in o rd e r

to s e a r c h f o r new t h r e s h o l d s i n the h a d r o n ic f i n a l s t a t e continuum, and

to s e a r c h d i r e c t l y f o r more J - l i k e p a r t i c l e s which appea r as sharp r e s o n a n c e s .

FIGURE 4.The reaction e+e~ -* hadrons in lowest order.

5) To s tu d y t h e topo logy o f h a d r o n ic ev en t s by measur ing

th e d i r e c t i o n and ene rgy of charged and n e u t r a l p a r t i c l e s . In p a r t i c u l a r ,

a t PETRA e n e r g i e s , t h e f r a g m e n ta t i o n o f hard g lu ons e m i t t e d i n a s s o c i a t i o n

w i t h q u a r k - a n t i q u a r k p a i r s l e a d s to the c r e a t i o n of a d d i t i o n a l g luons and

q u a r k s , r e s u l t i n g i n t h e p r o d u c t i o n of m u l t i - j e t e v e n t s . Study of the

p r o p e r t i e s of t h e s e j e t s e n a b l e s us to make a d i r e c t comparison w i th the

p r e d i c t i o n s o f QCD [ 7 ] . The r a t e o f 3 - j e t e v e n t s r e l a t i v e to 2 ~ je t e v e n t s

e n a b l e s us to measure d i r e c t l y t h e s t r o n g i n t e r a c t i o n c o u p l in g c o n s t a n t a

- 12-

6) To measure Che charge asymmetry expec ted from the i n t e r f e r e n c e"f*

o f weak and e l e c t r o m a g n e t i c i n t e r a c t i o n s i n the p r o d u c t i o n of y U p a i r s .

As shown in F ig . 5, diagrams i n which a v i r t u a l photon i s exchanged or

i n which a Z° v e c t o r boson i s exchanged bo th c o n t r i b u t e to p r o d u c t i o n .

FIGURE 5.First order electromagnetic and weak processes contributing

+ — + — to the reaction a e -* pi y

The i n t e r f e r e n c e can be unders tood i n terms of a v a r i e t y of models based

on the weak i n t e r a c t i o n Lagrang ian

Li n t = ^ (8v ' gA ^ VjZT*

2 2In the s imple V-A model f o r example, one assumes g = g. = g, where g /MV A i*m G / / 2 , and where G i s th e Fermi co u p l in g c o n s t a n t . I n the now s t a n d a r d

Glashow-Weinberg-Salara (GWS) model the coup l ings a r e ex p re s sed i n terms

of th e s i n g l e param ete r Q , the Weinberg an g le :

gv « 1/4 g cos 0W (3 t a n 2©w~ l ) , and gA » 1 /4 g sec Q .

In o r d e r to d i s t i n g u i s h between t h e o r e t i c a l hypoth .’. se s , we can use thea_ " a+

forw ard -backw ard ch a rg e asymmetry A- ---------;-, where a (o ) co r re sp o n d s0 + 0 — +— -f-

t o t h e y ( m ) a p p e a r in g i n the forwavd hemisphere. At / s = 30 GeV, w i th

38 *"? 4a t o t a l t ime - i n t e g r a t e d l u m in o s i ty o f 10 cm one o b t a i n s ~ 10 e v e n t s

i n a 4tt d e t e c t o r , l e a d i n g to a 10 s t a n d a rd d e v i a t i o n asymmetry e f f e c t i n

the V-A model and a 5 standard deviation effect in the GWS model [6].

Because the expec ted asymmetry i s sm a l l and because h i g h e r o r d e r QED

p ro c e s s e s a l s o produce s i z a b l e charge asymmetry a t Small a n g l e s , t h e meas­

urement of asymmetry r e q u i r e s a t t e n t i o n in r e d u c i n g and u n d e r s t a n d i n g sys tem ­

a t i c e r r o r s i n t h e d e t e c t o r d e s ig n .

One n o t e s t h a t b e f o r e the d i r e c t o b s e r v a t i o n of t h e Z° , t h e p r e c i s e

d e t e r m i n a t i o n of the charge asymmetry a r i s i n g from w e a k - e l e c t r o m a g n e t i c

i n t e r f e r e n c e i s t h e most im p o r ta n t v e r i f i c a t i o n o f the i d e a of t h e u n i f i e d

e l e c t r o m a g n e t i c and weak th e o ry .

3 .2 The D e te c to r

a) Overview

The MARK J d e t e c t o r i s shown in F ig s . 6 -10 . I t i s d e s ig n e d to

d i s t i n g u i s h charged hadrona , e l e c t r o n s , muons, n e u t r a l h ad ro n s and photons

and t o measure t h e i r d i r e c t i o n s and e n e r g i e s . I t c o v e r s a s o l i d a n g l e of

j> = 2u and 0 = 12° to 168° (0 i s the p o l a r and <J> i s t h e a z i m u t h a l a n g l e ) .

The d e t e c t o r , which c o n s i s t s of f i v e m agne t ized i r o n t o r o i d s b u i l t around

a non-magnetic i n n e r d e t e c t o r complemented by end c a p s , was d e s ig n e d to be

i n s e n s i t i v e to t h e e f f e c t s of s y n c h ro t ro n r a d i a t i o n . P a r t i c l e s l e a v i n g the

i n t e r a c t i o n r e g i o n f i r s t p a s s th rough a f i v e m i l l i m e t e r t h i c k aluminium

beam p ip ^ , w i th an o u t e r d ia m e te r of 190 nun. The a p e r t u r e o f the

beam p ip e i s l a r g e enough so t h a t th e s y n c h r o t r o n r a d i a t i o n produced i n

the f i n a l PETRA bending magnets and qu ad ru p o le s w i l l pass u n o b s t r u c t e d

th rough th e e n t i r e d e t e c t o r . Two t h i c k copper a b s o r b e r s a r e l o c a t e d sym­

m e t r i c a l l y around th e I n t e r a c t i o n r e g io n , a t a d i s t a n c e of 1 m e t e r , to t r a p

s y n c h ro t ro n r a d i a t i o n r e f l e c t e d back towards t h e i n t e r a c t i o n r e g i o n by

c o l l i m a t o r s j u s t i n f r o n t of t h e l a s t PETRA q u ad ru p o le s .

M A R K i - D E T E C T O R

FIGURE 6.The MARK J detector in a side view.

-14-

M A R K J - D E T E C T O R(Cross Section)

©CD© SHOWER CMWTERS (D TRIGGER COUNTERS <g) OMFTTtffiES d ) DRtfT CHAMBERS, MEDIAN

® ® DRIFT CHAMBERS. OUTER © © DRIFT CHAMBERS, INNER

© BEAM PIPE (?) MAGNETRON

(D A?-RING © MULTIPLIERS

WEIGHT [total] : -U B t MAGNETIC FIELD: 18 T

PARTICIPANTS:RWTH-Aachtn DESY -Hamburg MIT-Cambridge NKHEf-Amsterdam HEPI-Peking

IQm

FIGURE 7.The MARK J detector in end view. Seam pipe (1). drift tubes (DT!, shower counters (A,B,C), inner drift chambers (S,T), calorimeter counters (K), outer drift chambers (Q,P,R), and magnetized iron (2).

FIGURE 8.

MARK J detector showing the outer drift chambers.

FIGURE 9.Aerial view of the MARK J showing movable cable supports.

FIGURE 10.

of the MARK J showing the inner chamber

The detector layer structure is best understood by referring to Fig. 11.

4 5 c m F e

1 5 c m F e

1 0 c m F e

2 . 5 c m F e

c = 1 2 X o _

B = 3 X o

A = 3 X o

1 0 P l a n e s

D r i f t c h a m b e i P

JBxdUTCKGxm

y.vuiv

D C c x i n t e r

Q

5SB

1 2 P l a n e s

D r i f t c h a m b e r

c — =i i n m m i i h i H i i u i ' m

e ~ — H * — e +

1 c m t h i c k

c a l o r i m e t e r

c o u n t e r s , K

S , T

5 m m P b

+ 5 m m

s c i n t i l l a t o r

d r i f t t u b e s

FIGURE 11.The layer structure of the MARK J detector as seen by a particle emerging from the Interaction point at a right angle to the beam axis.

During th e f i r s t n in e months of o p e r a t i o n , a r i n g of 2 x 16 l u c i t e Cerenkov

c o u n t e r s each cover ing an az im u th a l s e c t o r o f 22 .5° and a p o l a r - a n g l e re g io n

from 9° < 0 < 171° su rrounded th e beam p ip e . These c o u n t e r s a r e d iv id e d

a t 0 * 90° to permi t a c rude d e t e r m i n a t i o n of the momentum b a l a n c e between

the forward and backward hem ispheres . The c o u n t e r s a r e i n s e n s i t i v e to the

e f f e c t s of s y n c h ro t ro n r a d i a t i o n and can be used to s e p a r a t e charged from

n e u t r a l p a r t i c l e s .

In the l a t t e r p a r t of 1979 the l u c i t e c o u n t e r s were r e p l a c e d by a

f o u r - l a y e r i n n e r t r a c k d e t e c t o r composed of 992 d r i f t t u b e s . Er.ch

tube i s 300 mm long and 10 mm wide and has a s p a t i a l r e s o l u t i o n o f 300

microns . The t u b e s , which a r e a r ranged p e r p e n d i c u l a r to the beam l i n e ,

d i s t i n g u i s h charged from n e u t r a l p a r t i c l e s i n the a n g u la r r ange 30° < 0

< 150° and r e c o n s t r u c t th e p o s i t i o n of the e v en t v e r t e x a lo n g the beam

l i n e to an accu racy of two m i l l i m e t e r s . The d i s t r i b u t i o n of ev e n t v e r t i c e s

o b ta in ed u s in g the d r i f t t u b e s i s shown i n F ig . 12. The obse rved r . m . s .

width o f 1.27 cm i s com pat ib le w i th t h a t expec ted from th e known bunch

l e n g th of the machine.

P a r t i c l e s then pass th rough 18 r a d i a t i o n l e n g t h s of shower c o u n te r s

used to i d e n t i f y and measure th e energy of e l e c t r o n s , p h o to n s , charged and

n e u t r a l had rons . This i n n e r c a l o r i m e t e r i s d iv i d e d i n t o t h r e e l a y e r s of

shower c o u n t e r s ( l a b e l l e d A, B and C i n F ig . 6 ) . Each c o u n t e r i s c o n s t r u c t e d

of 5 .0 mm t h i c k p ie c e s of s c i n t i l l a t o r a l t e r n a t e d w i th le a d p l a t e s of equal

t h i c k n e s s . The A and B c o u n t e r s a r e each 3 r a d i a t i o n l e n g t h s t h i c k , w h i le

t h e C shower c o u n te r i s a t o t a l of 12 r a d i a t i o n l e n g th s t h i c k ( measured

normal t o t h e s u r f a c e of the c o u n t e r ) .

The tw en ty A shower c o u n t e r s a r e each 2 m long and cover t h e a n g u l a r

r e g i o n o f 0 a 12° t o 168°. The 24 B c o u n t e r s a r e c o n s t r u c t e d i d e n t i c a l l y to

t h e A c o u n t e r s and cover an a n g u l a r r e g i o n from 0 a 16° to I f 4 ° .

- 2 1 -

- 5 0 5 z ( c m )FIGURE 12.

Distribution of event vertices along tho beam direction reconstructed using drift tube tracks.

S ince every shower c o u n te r i s viewed by one pho to tube a t each end , the

l o n g i t u d i n a l (z) p o s i t i o n of p a r t i c l e t r a j e c t o r i e s can be de termined by

comparing th e r e l a t i v e p u l s e h e i g h t s from each end of t h e c o u n t e r . Timing

I n f o r m a t io n p ro v id e s a n o t h e r measure o f the l o n g i t u d i n a l p o s i t i o n . The

t r a j e c t o r y l o c a t i o n de te rm ined by t h i s method was found to be in e x c e l l e n t

agreement w i th the d a t a from the d r i f t tube s ( see S e c t io n 3 , 3 a ) .

Twelve p la n e s of d r i f t chambers ( l a b e l l e d S and T) measure th e ' ing les

of p a r t i c l e s p e n e t r a t i n g the i n n e r e l e c t r o m a g n e t i c c a l o r i m e t e r . Each of

t h e s en s e w i r e s i s connec ted to i t s own a m p l i f i e r and t ime d i g i t i z e r . Both

end cap regions are covered by an additional ten planes of drift chambers

(labelled U and V) of similar construction. These chambers are protected

from beam backgrounds from the interaction region by the shower counters

A, B and C. The energy sampling elements of the calorimeter K, shown in

Fig. 6, are 192 scintillation counters arr^Aged in four layers. The main

body of the calorimeter is composed of the magnetized iron plates

which are also used to momentum-anaiyze muons. These plates range in thick­

ness from 2.5 to 15 cm. Hadrons penetrating the inner shower counter layers,

and secondary particles produced by hadronic showers initiated in the inner

layers, deposit most of their remaining energy in the calorimeter K. The

energy sampled by the K counters is thus usod to help distinguish hadrons

from electrons, and to help identify minimum-ionizing particles.

Muons are identified by their ability to penetrate the iron of the

hadron calorimeter. The low-momentum cut-off is about 1.3 GeV/c at normal

incidence. The Initial muon trajectory is measured in the S and T (U and V)

chambers and in the drift tubes.

The bend an^le and position of muons exiting from the calorimeter are

measured in 10 planes of drift chambers, labelled R and P in Vig. 6. The total

thickness of the iron is 87 cm and it has a bending power of approximately

17 kG-meters. The typical bend angle for a 15 GeV muon is 30 mrad.

An additional 2 layers of drift chambers (Q chambers) are situated amidst

the iron layers to measure the muon tracks in the bending plane. Adjacent

to these chambers are the 32 muon trigger counters marked (D) used to trigger

on single and multiple muon events and to reject cosmic rays. Each of these

counters is 30 cm wide and 450 cm long and has a phototube at each end. The

timing difference between real dimuon events and cosmic rays is about 10 ns.

These counters have a timing resolution of 400 ps.

Covering each of t h e end cap r e g io n s a r e th e E c o u n t e r hodoscopes . Each

of th e s e c o u n t e r s has d im ens ions 80 cm x 450 cm x 1 cm and they a r e used

to t r i g g e r on muons produced i n th e forward and backward d i r e c t i o n s as w e l l

as to r e j e c t cosmic r a y s and beam-gas background.

One of t h e prime g o a l s of th e MARK J e x p e r i m e n t a l program (see s e c t i o n

3 .1) i s to measure the charge asymmetry i n t h e a n g u l a r d i s t r i b u t i o n of muon

p a i r s produced i n e e a n n i h i l a t i o n to an a c c u r a c y o f ^1%. T h i s goa l can

only be ach ieved i f smal l s y s t e m a t i c e f f e c t s due to v a r i a t i o n s in chamber

e f f i c i e n c y and c o u n te r g a i n s , and s l i g h t asym m etr ie s i n t h e c o n s t r u c t i o n

of t h e magnet and the p o s i t i o n s of p a r t i c l e d e t e c t o r s in s p a c e , do no t i n f l u e n c e

the o v e r a l l charge asymmetry measurement. In o r d e r to i s o l a t e and s u b s e q u e n t ly

e l i m i n a t e the e f f e c t s of t h e s e s y s t e m a t i c e r r o r s in the measurement , the sup­

p o r t i n g s t r u c t u r e i s de s igned so t h a t t h e e n t i r e d e t e c t o r can b e r o ­

t a t e d a z i m u th a l !y about the beam l i n e by +90° and 180° about a v e r t i c a l a x i s .

The r o t a t i o n about the v e r t i c a l a x i s maps 0 i n t o 180° - 0, and i s t h e r e f o r e

most u s e f u l in checking the measurement of the f r o n t - b a c k ch a rg e asymmetry.

The az im u th a l r o t a t i o n , which i s used to check f o r beam p o l a r i z a t i o n , can a l s o

be used to a id in the charge asymmetry measurement in the p re s e n c e of p o l a r i z e d

beams,

For the data in this report detectors E and R were not used.

b) The Lumi n o s i t y Monitor

The l u m i n o s i t y mon i to r c o n s i s t s of two a r r a y s o f tw e n t y - e i g h t le ad g l a s s

b lo c k s [ 8 ] ( l a b e l l e d G i n F ig . 6 ) , each w i th d im ens ions o f 8 cm x 8 cm x 70

cm lo c a t e d 5 .8 m from the i n t e r a c t i o n p o i n t . They a r e des ig n ed to measure

Bhabha e v e n t s a t sm al l s c a t t e r i n g a n g le s (~30 mrad) . S c i n t i l l a t o r s (F) in f r o n t of

the l e a d g l a s s d e f i n e the a c c e p ta n c e and the le a d g l a s s c o u n t e r s measure the

energy of th e e l e c t r o n p a i r s .

For o n - l i n e l u m in o s i ty measurements , o n ly the s i g n a l s from th e le a d g l a s s

a r e used . The t r i g g e r demands s i g n a l s in bo th th e forward ( i . e . i n t h e d i r e c t i o n

- 23 -

of the e l e c t r o n s ) and backward hodoscopes w i th a minimum of 20% o f th e

beam energy d e t e c t e d i n each c o u n t e r a r r a y .

In th e o f f - l i n e a n a l y s i s , t h e s i g n a l s from t h e le a d g l a s s a r e used in

c o n n e c t io n w i th t h o s e coming from s i x t e e n a c c e p t a n c e - d e f i n i n g s c i n t i l l a t i o n

c o u n t e r s p a i r e d t o form e i g h t m o n i to r in g s t a t i o n s .

Each l u m i n o s i t y m o n i to r in g s t a t i o n c o n s i s t s o f a sm al l (60 mm x 30 mm

x 5 mm) s c i n t i l l a t o r behind which a l a r g e r c o u n t e r (80 mm x 50 mm x 5 mm)

i s c e n t e r e d , aivery F c o u n te r i s g lue d t o a t h i n aluminum f i n g e r t i l t e d

so t h a t the c o u n t e r s a r e p e r p e n d i c u l a r to p a r t i c l e s o r i g i n a t i n g from the

i n t e r a c t i o n r e g i o n . The l a r g e r s c i n t i l l a t o r i s viewed by a XP2230/B pho to tube

v i a an a i r l i g h t g u id e ; the s m a l l e r s c i n t i l l a t o r i s viewed by a s e p a r a t e tube

or t h e same type v i a an a i r - l u c i t e h y b r id l i g h t g u id e . Care was ta k en so t h a t

th e l a r g e s c i n t i l l a t o r does n o t l i e i n th e shadow of th e l u c i t e l i g h t guide

o f i t s companion. Four m o n i to r in g s t a t i o n s a re mounted in the forward r e g i o n

and four the backward r e g io n such t h a t o p p o s i t e p a i r s of c o u n t e r s l i e in

the h o r i z o n t a l o r v e r t i c a l p la n e .

The s i z e of che sm al l s c i n t i l l a t o r s was chosen t o g iv e an a c c e p t a b l e

c o u n t in g r a t e g iv e n th e machine l u m i n o s i t y and t h e s c a t t e r i n g a n g l e . The t y p i c a l

s i n g l e s co u n t in g r a t e i n each of t h e m o n i to r in g s t a t i o n s i s 100 kHz. The

d im en s io n s o f t h e l a r g e s c i n t i l l a t o r were then chosen to minimize the r a d i a t i v e

c o r r e c t i o n s ( see s e c t i o n 3.3d) The s c i n t i l l a t o r s were machined w i th a diamond

c u t t i n g t o o l to a t o l e r a n c e of ± 50 m icrons and t h e machined s u r f a c e d id not

r e q u i r e p o l i s h i n g . A f t e r m ach in ing , t h e s i z e s o f t h e s c i n t i l l a t o r s were measured

t o an a c c u r a c y o f ± 5 m ic rons .

Because t h e Bhabha c r o s s s e c t i o n a t sm a l l s c a t t e r i n g a n g l e s i s p r o p o r t i o n a l

-4t o 0 i t i s n e c e s s a r y to know a s p r e c i s e l y as p o s s i b l e the p o s i t i o n s of the

s c i n t i l l a t o r s w i t h r e s p e c t t o t h e beam d i r e c t i o n . Crawford e t a l . , [ 9 3 have

- 25 -

shown, however, t h a t i f s c i n t i l l a t o r s on o p p o s i t e s i d e s of t h e beam l i n e

a r e mounted such t h a t t h e i r s e p a r a t i o n remains f i x e d , f i r s t o r d e r e f f e c t s

due to d i s p l a c e m e n t s and a n g u l a r r o t a t i o n s o f m on i to r c o u n t e r s w i th r e s p e c t

to th e beam l i n e c a n c e l o u t . Th is was r e a l i z e d i n t h i s i n s t a n c e by mounting

a l l f o u r of t h e m o n i to r in g s t a t i o n s a t one end of th e d e t e c t o r on a common

frame. The s e p a r a t i o n be tween o p p o s i t e m o n i to r in g s t a t i o n s was then measured

u s in g a p r e c i s i o n t a b l e and a h e i g h t gauge w i th an i n t r i n s i c s e t t i n g e r r o r of

20 m ic rons . The p o s i t i o n of the frame i n th e e x p e r i m e n t a l h a l l can then be

measured to an acc u racy of 200 y. D e t a i l s of the c a l c u l a t i o n of the r a d i a t i v e 1,

c o r r e c t i o n s f o r t h i s m on i to r a r e g iv e n i n S e c t i o n 3 .3d .

c ) The D r i f t Chambers

The d e s ig n o f th e d r i f t chambers was d i c t a t e d by th e need fo r m echan ica l

s i m p l i c i t y and s t r e n g t h t o g e t h e r w i th the n e c e s s i t y to cover a very l a r g e s o l i d ang le

[10 ] . P r e v io u s to th e exper im en t a t PETRA, chambers of i d e n t i c a l c o n s t r u c t i o n

had been used s u c c e s s f u l l y over a p e r io d o f t h r e e y e a r s in an exper iment [11]

a t t h e CERN I n t e r s e c t i n g S to rage R ings . Cu ?:he b a s i s o f th e ex p e r i e n c e ga ined

a t CERN, t h e MARK J chambers f o r PF.TRA were c o n s t r u c t e d ir> s e v e r a l c o n f i g u r a t i o n s :

tw elve l a y e r (S and T) o r t e n l a y e r (U and V) chambers to measure t r a c k s b e fo re

they e n t e r the m agne t ized i t o n , v e ry l a r g e chambers w i th t e n l a y e r s (P) or s i x ­

t e e n l a y e r s (R) to measure t h e t r a c k s a f t e r l e a v i n g th e i r o n , and two l a y e r

s ampl ing chambers (Q) t o measure t h e t r a c k s i n th e bending d i r e c t i o n halfway

th rough t h e i r o n . For t h i s a p p l i c a t i o n t h e chambers used had to be l a r g e ind

r i g i d w i t h l i t t l e dead space occup ied by s t r u c t u r a l e l em en t s . The amount of

m a t e r i a l i n t h e chamber a lo n g the p a t h o f th e p a r t i c l e s was n o t a c o n s i d e r a t i o n ,

s in c e i t i s n e g l i g i b l e compared w i th the m a t e r i a l i n t h e i r o n . The s o l u t i o n

waj t o c o n s t r u c t chambers w i th 10 cm c e l l s formed by two f i e l d - s h a p i n g I-beams

(which provide the structural strength) glued with insulators between two

aluminium ground plates. A coordinate is measured by a double layer of such

cells, with the second layer displaced by half a cell width from the first

to resolve the left-right ambiguity. This double layer is normally glued to

another double layer formed by I-beams running in the perpendicular direction,

which add additional strength as well as measuring the perpendicular coordinate.

Because the electric field in the drift chamber cell is non-uniform, and the

relation between time and position is not linear for inclined tracks, the

positions must be corrected for angle during track reconstruction.

Individual cells have been tested to give a resolution of 0.4 mm for

perpendicular tracks. In our system of 5000 wires with individually calibrated

TDC's we find that for all angles of incidence the average resolution is about

0.6 mm. This is much smaller than the spread resulting from multiple scattering

in the iron.

The drift chambers contain 50 cubic meters of a gas mixture composed of

75% argon and 25% isobutane. To reduce the gas consumption for this large volume

we have installed a partially recirculating gas system. This circulates the

entire gas volume through the chambers every four hours. Water is removed by

a molecular sieve filter and oxygen is removed by a catalytic converter fed

with a small amount of hydrogen. Other contaminants are removed by replacing

10% of the gas with fresh gas each circulation cycle. The isobutane content of

the gas is monitored continuously by an infrared gas analyzer and maintained at

(25.0 ± 0.1)%. The oxygen is monitored by a fuel cell and kept below 20ppm in

the return gas from the chambers. The gas is also analyzed automatically every

two hours by a Hewlett-Packard 5840A programmable gas chromatograph so that

water, nitrogen, light hydrocarbons and other contaminants can be monitored.

The nitrogen is not removed by the purification system and thus provides a means

of estimating the amount of contamination from air, either through leakage,

- 2 6 -

supply . The n i t r o g e n c o n t e n t normal ly rem ains below 500ppm.

d ) The T r ig g e r

The t r i g g e r i s a r ranged in two s t a g e s . The f i r s t s t a g e i s a f a s t loose

t r i g g e r g e n e r a t e d from th e c o u n te r h i t i n f o r m a t i o n w i t h t h e f o l l o w i n g r e q u i r e ­

ments:

i ) For e l e c t r o n p a i r s we r e q u i r e a t l e a s t 0 .5 GeV t o t a l energy d e p o s i t e d

in o p p o s i t e q u a d r a n t s o f the A and B c o u n t e r s .

i i ) For muon p a i r s we require, a t l e a s t two A and two B c o u n t e r s in c o i n ­

c idence w i th a p a i r of D c o u n t e r s which a r e c o p l a n a r w i t h i n 50°.

i i i ) For s i n g l e muon ev en t s we r e q u i r e a t l e a s t two A, two B, two C and

one D c o u n t e r s to be t r i g g e r e d .

iv ) For hadrons we r e q u i r e a t l e a s t fo u r A and t h r e e B c o u n t e r s ; each

t r i g g e r e d quadran t must be In c o in c id e n c e w i t h t h e o p p o s i t e q u a d r a n t .

A l l t r i g g e r s a r e r e q u i r e d to be i n c o i n c i d e n c e w i t h t h e beam c r o s s i n g s i g n a l .

A f t e r t h e f a s t t r i g g e r , a second s t a g e imposes two more s e l e c t i o n s depend­

ing on e v en t type . For e l e c t r o n p a i r s and hadron e v e n t s th e t o t a l energy de ­

p o s i t e d in t h e i n n e r c a l o r i m e t e r s A, B and C i s d e te rm in e d by m easur ing the p u l s e

a r e a o f l i n e a r l y added s i g n a l s . We r e q u i r e a t l e a s t 13% of the t o t a l C.M.S.

energy f o r hadrons and a t l e a s t 10% f o r e l e c t r o n p a i r e v e n t s . For muon p a i r s ,

s i n g l e muon and hadron e v e n t s , a m i c r o p r o c e s s o r ( S e c t i o n 3 . 2 f ) a p p l i e s a l o o s e

t r a c k r e q u i r e m e n t demanding a t l e a s t t h r e e p a i r s o f w i r e s t o be h i t i n th e S

o r T chambers.

- 2 7 -

diffusion through the plastic supply lines, or from its presence in the gas

- 2 8 -

In a d e t e c t o r of t h i s ty p e i n which ev e n t i d e n t i f i c a t i o n and energy

measurement depends on th e d e t a i l e d re sponse of c a l o r i m e t e r c o u n t e r s , i t

i s e s s e n t i a l t h a t the b e h a v i o r of c o u n t e r packages be i n v e s t i g a t e d in p a r t i c l e

beams o f v a r i o u s types and e n e r g i e s . Thus, one quadran t o f t h e com­

p l e t e A, B, C and K assembly was reassembled a t CERN and s e t up on a movable

t a b l e i n a t e s t beam, The r e sponse of the c o u n t e r s to e l e c t r o n s , p ions and

muons o f v a r i o u s e n e r g i e s , i n c i d e n t a n g le s ana p o s i t i o n s was meas­

u re d . The i n c i it- beam was d e f in e d by t h r e e sm a l l s c i n t i l l a t i o n c o u n te r s

and c o l l i m a t e d to a s i z e of 2 cm x 2 cm on th e c o u n t e r s , E l e c t r o n s and p io n s

were d i s c r i m i n a t e d by two Cerenkov c o u n te r s f i l l e d w i th he l ium o r a i r , and

muons were i d e n t i f i e d by t h e i r p e n e t r a t i o n o f a d d i t i o n a l i r o n a b s o r b e r s . A l l

pho to tube g a in s were a d j u s t e d by n o rm a l iz in g the p u l s e n e i g h t to t h a t o b ta in e d

from muons I n j e c t e d no rm al ly a t th e c e n t e r o f the c o u n t e r . A t o t a l of 200

s p e c t r a co v e r in g a range of beam momenta from 0 .5 to 10 .0 GeV and the a n g u la r

ranges 15° j< 0 _< 90^, 0° £ <f> < 45° were measured. P u ls e h e i g h t and t iming

of each pho to tube were r e c o rd e d on magne tic t a p e s and a n a ly z e d o f f l i n e . The

r e s p o n s e o f th e A, B, C and K a r r a y s was then a s s e s s e d by combining t h e i r p u l s e

h e i g h t s w i th p ro p e r w e igh t s chosen to o p t im iz e th e energy r e s o l u t i o n .

To r e l a t e t h e p u l s e h e i g h t i n th e p h o to tu b e s of e a c h c o u n te r of the A, B

and C a r r a y s to th e d e p o s i t e d energy , the s i g n a l s o f the two tu b e s a r e added,

and th e l i g h t a t t e n u a t i o n i n the s c i n t i l l a t o r i s t aken i n t o a c c o u n t . The a t t e n ­

u a t i o n l e n g t h i s measured to be 102 cm f o r A and B c o u n t e r s and 109 cm f o r C

c o u n t e r s . W i th in t h e a c c e p ta n c e of C c o u n t e r s , l i n e a r i t y f o r bo th i n c i d e n t

e l e c t r o n s and i n c i d e n t p i o n s improves s l i g h t l y a t s m a l l e r 0 a n g l e s due to t h e

i n c r e a s e o f t h e e f f e c t i v e t h i c k n e s s of t h e c a l o r i m e t e r , w h i l e no c l e a r d e g ra d in g

o f t h e r e s o l u t i o n i s o b s e r v e d . The h i t p o s i t i o n i n the c o u n t e r can be r e c o n s t r u c t e d

e) Detector Calibration

-29-

from bo th the t im ing d i f f e r e n c e and p u l s e h e i g h t asymmetry of th e p h o to tu b e s

a t each end of the counter . , The r . m . a . p o s i t i o n r e s o l u t i o n of bo th A and

B c o u n te r s i s 2 ,5 cm from t im ing measurement and 6 cm from p u l s e h e i g h t meas­

urement, Combination of t h e two measurements g iv e s an a n g u l a r r e s o l u t i o n

b e t t e r than 5° f o r the f u l l a c c e p ta n c e of A and B c o u n t e r s .

f ) O n- l ine Data C o l l e c t i o n and Data M on i to r ing

The expe r im en ta l d a t a from the d e t e c t o r a r e read i n th rough two main

CAMAC branches ( F i g .13). Branch A i n c l u d e s two c r a t c s of s c a l e r s which

m oni to r 300 s i n g l e s r a t e s from th e c o u n t e r s , and 100 c o i n c id e n c e r a t e s

and h igh v o l t a g e s in t h e c o u n t e r power s u p p l i e s . Th is b ranch i s

t ime d r iv e n ; i t i s r ead and c l e a r e d every 100 se c o n d s . Branch

B i s t r i g g e r d r iv e n ; i t c o n s i s t s of f i f t e e n CAMAC c r a t e s d iv i d e d i n t o v.hree

sub-b ranches which a r e connec ted to t h e main b ran ch th ro u g h t h r e e b ranch

s e l e c t o r s of the CERN type» On t h i s b ra n c h , a l l t h e c o u n t e r TDC’ s , ADC's,

and the d r i f t tube and chamber TDC’s a r e read o u t .

The above two b ranche s A and B a r e i n t e r f a c e d to t h e o n l i n e computer

v i a two s e p a r a t e microprogrammable b ran ch d r i v e r s (MBD), each of which i s

a comple te so f tw a re programmable m i c r o p r o c e s s o r .

For branch B, t h e m i c r o p r o c e s s o r i s used to p r e s e l e c t even t c a n d i d a t e s

and to suppress s p u r i o u s i n f o r m a t i o n , a s d e s c r i b e d b r i e f l y in s e c t i o n 3.2do

The m as te r t r i g g e r s i g n a l , c o r r e s p o n d in g t o th e l o g i c a l OR o f the f i v e f a s t

e l e c t r o n i c s t r i g g e r s d e s c r i b e d e a r l i e r , i s s e n t to a CAMAC i n p u t r e g i s t e r ,

and i t i n i t i a t e s t h e m ic roprocesso r , . The m ic ro p r o c e s s o r f i r s t r eads t h e d a t a

from the d r i f t chamber t l m e - d i g i t i z e r e l e c t r o n i c s i n t o i t s own memory, and

then r eads an i n p u t r e g i s t e r to s ee which k ind o f t r i g g e r has o c c u r r e d . I f

i t i s e i t h e r a l u m i n o s i t y m on i to r o r e l e c t r o n p a i r t r i g g e r , i t d i r e c t l y r e a d s

BRANCH Ai C A L E R ^ -

i T ,--------------- 1 BRANCH BT[ A

i R E C O R D PRINTERPLOTTER

STORAGE SCOPE FOR L, IS P L A Y

M

0

N1

TO

R

COLOR VIDEO

MONITORS

r ..........."

i....—..... “

j I

u

r----------- -lIL___— -

f------------)i

i. . . . r-

V»r .......... t*

*.......... *

7

PDP ]/5 5

U

N

t

■B.U

S

CONSOLE

VIDEOTERMINAL

13.5M byteSYSTEM DISK

13.5M byte STORAGE and ONLINE MONITOR

F IL E S0.5M byte F IX E D -H E A D DISK for HISTOGRAMS

1600 bpi9 TRACK M A G -D R IV E

LINK to IBM

C

o

N T R &

s

T

O

RAGE

O

u

TPUT

FIGURE 13.

Schematic of online computer and peripherals configurations.

i n and w r i t e s o u t a l l t h e CAMAC d a t a to th e o n l i n e computer . I f the t r i g g e r

i s a s i n g l e muon, muon p a i r o r hadron t r i g g e r , a w ire p a i r t e s t i s c a r r i e d out

in t h e m i c r o p r o c e s s o r * That i s , i t s cans th ro u g h th e d r i f t chamber d a t a s t o r e d

i n i t s memory and t e s t s t o d e te rm in e t h e number of double p l a n e s in the in n e r

d e t e c t o r which have a d j a c e n t h i t s . I f t h e number i s l e s s than t h r e e , the even):

i s r e j e c t e d . O the rw ise , i t i s r ead i n t o th e computer . The f low diagram of t h i s

program i s shown i n F ig . 14.

I ISTART

± _ _ _ [c l e a r d a t a cr a t e s ]

___ Z Z f ................. -SIGNAL COMPUTER READY

JWAIT FOR TR IG G ER ' ‘1

: : ......... — TRIGGERREAD DRIFT CHAMBERS INTO MBD MEMORY

READ INTRIGGERBITWORD

LUMINOSITYMONITORB H A B H A

- W H A T KIND OF

TRIGGER.

YES

TWO u.SINGLE ll HADRON

.......... i _______READ IN PAIR REQUIREMENT

READ IN AND W R ITE TO P D P C O U N TER

ADC.TDC W R IT E TO P D P D R IF T CHAMBER TDC's

FIGURE 14.Block diagram showing microprocessor program logic for trigger handling.

As th e m ic ro p ro c e s s o r r e a d s i n the coun te r i n f o r m a t i o n , i t d e c id e s whether

each d a t a word i s u s e f u l ; whether i t i s g r e a t e r than the p e d e s t a l v a l u e in the

ca s e of the ADC's, o r whe ther i t i s l e s s than th e ove r f low v a l u e in t h e case

of the TDC’ s . Only when th e d a t a a r e v a l i d a r e th e y w r i t t e n i n t o th e computer .

Thus, th e av e ra g e l e n g th of a t r i g g e r i s on ly about 400 1 6 - b i t words. This

a l s o d e c r e a s e s t h e deadtime due to d a t a t r a n s f e r . For t r i g g e r s which a r e accep ted

the deadt im e i s about 30 msec. For those r e j e c t e d i t i s t y p i c a l l y 3 msec.

The o n l i n e computer i s a PDP 11/55 (F ig . 13) . In a d d i t i o n to w r i t i n g

d a t a to m agne t ic t a p e , s e l e c t e d q u a n t i t i e s a r e histogrammed and d i s p l a y e d o n l in e

on c o l o r v ideo m o n i to r s . The h i s to g ra m s a r e a l s o p r i n t e d ou t i n h a r d c o p i e s fo r

r e c o r d . S e l e c t e d c o in c id en c e r a t e s a r e moni to red c o n s t a n t l y . I f any of them

i s ou t of p r e s e t l i m i t s , warning messages a r e d i s p l a y e d .

30 -2 ~1At a beam lu m in o s i ty of 1 x 10 cm sec , depending on the beam c o n d i t i o n s ,

t y p i c a l t r i g g e r r a t e from the f a s t e l e c t r o n i c s i s 5 Hz. A f t e r m ic ro p ro c e s s o r

p r e s e l e c t i o n , the d a t a r a t e w r i t t e n on magnet ic ta pe i s 2 Hz. Thr* r e s u l t i n g

deadt im e i s about 5%.

In a d d i t i o n to th e pu re ly o n l i n e fu n c t i o n s th e PDP11 i s used between runs

and d u r in g shutdowns f o r c a l i b r a t i n g the t i m e - d i g i t i z i n g e l e c t r o n i c s f o r the

d r i f t chambers and c o u n t e r s , and the p u l s e h e i g h t d i g i t i z i n g e l e c t r o n i c s fo r

t h e c o u n t e r s .

- 3 3 -

This s e c t i o n g iv e s a b r i e f d e s c r i p t i o n of the methods used to

c a l c u l a t e t h e energy and d i r e c t i o n of ' 'he p a r t i c l e s seen by th e d e t e c t o r

and o f t h e p ro c e d u re s used to s e l e c t t h e e v e n t s of i n t e r e s t . In a d d i t i o n

we d i s c u s s th e Monte Car lo s im u l a t i o n of the observed p r o c e s s e s , and

r a d i a t i v e c o r r e c t i o n s a p p l i e d to th e e x p e r im e n ta l d a t a .

a ) D i r e c t i o n and Energy Mea surements

The A, B, C and D c o u n t e r s (F igu re 6) have a p h o to tu b e a t each end.

The p o s i t i o n of th e t r a c k a long the z d i r e c t i o n of the c o u n t e r can thus

be de te rm ined by use of t h e p u l s e h e i g h t (ADC) and t ime (TDC) d i f f e r e n c e s

measured by th e se tu b e s . Combined w i th the p o s i t i o n of t h e i n t e r s e c t i o n

r e g i o n , t h i s g ive s t h e p o l a r a n g le 0 of t h e t r a c k . The a t t e n u a t i o n

lengch of t h e c o u n t e r s , which i s needed f o r the ADC p o s i t i o n measure­

ment, was measured in t h e t e s t beam as d e s c r i b e d in S e c t io n 3 . 2 e . I t i s

'vlOO cm f o r t h e A, B, and C c o u n t e r s and ^180 cm f o r t h e D c o u n t e r s .

The p o s i t i o n deduced from th e TDC measurement u s e s a l i g h t p r o p a g a t io n

speed of ^16 cm/nsec. Th is was a l s o de te rm ined from t e s t beam d a t a .

C o r r e c t i o n s f o r th e dependence of th e TDC o u tp u t s i g n a l on in p u t p u l s e

h e i g h t and f o r t ime o f f l i g h t a r e a p p l i e d , A weighted ave rage of the two

p o s i t i o n measurements i s th e n t a k e n . These p o s i t i o n e s t i m a t e s have a l so

been checked w i th t h e r e c e n t l y i n s t a l l e d d r i f t t u b e s , An example i s

shown In F ig u re 15a, where t h e d i f f e r e n c e between the p o s i t i o n of the h i t

in t h e A c o u n t e r s a s d e te rm ined from ADC and TDC, and th e p o s i t i o n expec ted

from th e more p r e c i s e t r a c k s f i t t e d in t h e d r i f t tube s i s p l o t t e d f o r 30

GeV Bhabha e v e n t s , As can be seen , t h e r . m . s . p o s i t i o n r e s o l u t i o n o b ta in ed

from th e c o u n t e r s i s ^ 2 .5 cm.

3.3 Off-line Analysis

even

ts

- 2 0 - 1 0 0 1 0 2 0

^ t u t T ^ c t r ( c m ) ® tu tf ® ctr E vis/ys"

FIGURE 15-Counter resolution for large angle Bhafaha scattering a t / s = 30 GeV.

a. Position of hits deduced from TDC and ADC information in the A counters compared toextrapolated tracks {ztu(3) observed in drift tubes.

b. Polar angles of reconstructed counter tracks compared to tracks fitted with drift tube information, c. Observed energy spectrum for large angle Bhabha scattering.

- 3 5 -

The az im u th a l ang le <)> i s de te rm ined by the p o s i t i o n of the c o u n t e r s

in bpace. The segm en ta t ion o f the c o u n te r l a y e r s c o r re sponds to a r e s o ­

l u t i o n of 'v'/0 in 4> fo r an i n d i v i d u a l h i t .

Counter t r a c k s a r e c o n s t r u c t e d w i th a v e c t o r energy f low computed

from the p u l s e h e i g h t and p o s i t i o n in fo rm a t io n of t h e groups of h i t s

o ccu r in g w i th i n a cone of 20° opening a n g l e , emanating from the i n t e r a c t i o n

p o i n t . In F igure 15b we show a comparison of the p o l a r ang le of the c o u n t e r

t r a c k , o b ta in ed from t h i s combinat ion of shower i n f o r m a t i o n , w i th t h a t

of the t r a c k f i t t e d in the d r i f t t u b e s . As can be s e e n , the r e s o l u t i o n i s

^3° .

The energy c o r re spond ing to the p u l s e h e i g h t r eco rded i n the

shower co u n te r s and c a l o r i m e t e r c o u n t e r s Is computed by t a k in g a w eighted

sum of th e ADC v a l u e s . The a p p r o p r i a t e weight f o r each l a y e r of c o u n t e r s

has been de termined from the a n a l y s i s of the t e s t beam d a t a d e s c r i b e d in

S e c t io n 3 .2e . The w eigh t s a r e d i f f e r e n t f o r h a d ro n ic and e l e c t r o m a g n e t i c

showers. F igure 15c shows the energy measured in t h i s way fo r e l e c t r o n s observed■f _ + _

a t l a r g e s c a t t e r i n g a n g le s i n e e -► e e a t 30 GeV. For had ron ic e v e n t s

t h e r . m . s . r e s o l u t i o n i n the t o t a l observed energy i s ^20% as can be seen

i n F igu re 16a. From c o u n te r t r a c k s th e t o t a l m i s s in g e n e r g i e s in the

d i r e c t i o n s p a r a l l e l and p e r p e n d i c u l a r to the beam, which a r e used i n the

even t s e l e c t i o n , may be computed. The observed d i s t r i b u t i o n s of th e s e

q u a n t i t i e s a r e shown i n F ig u re s 16b and 16c f o r h ig h energy hadron e v e n t s .

x = E ^ s ! E c m s x = E ± l E v jS X = E / 7 / E v j s

FIGURE 16.

Energy measurement at / s = 30 GeV. The solid curves are predictions of Monte Carlo computations.a. Visible energy spectrum for hadronic events.b. Energy imbalance E j jn the direction transverse to the beam.c. Energy imbalance E^ in the beam direction.

-37-

b) O ff -L ine Data R educ t ion

The d a t a a r e reduced in a s e r i e s of t h r e e p a s s e s . Diagrams

r e p r e s e n t i n g th e g e n e r a l a r rangem en t of the d a t a r e d u c t i o n p r o c e s s and

i l l u s t r a t i n g two of th e s e p a s s e s a r e shown i n F ig u r e 17. The f i r s t pa s s

i s a f a s t f i l t e r f o r hadron and muon ev en t s . For hadron e v e n t s , the

energy i s c a l c u l a t e d rough ly , and a cu t a t 25% of t h e c e n t e r of mass

PASS 1 F ILTERS PASS 2 HAORON FILTER

HADRON FILTER MUON FILTER

RAW DATA TAPE (- 60k events processed m - 2min on IBM 370/168)

r

$TRIGGER SELECTION

$

TOTAL ENERGY CUT Ev,s > 0.25/s*

CRUDE b' aI anCE CUT' USING ENERGV PER DETECTOR QUADRANT

$

PASS 1 HADRON SAMPLE ~ 1 8 V. of data

MINIMUM NR OF HITS IN OUTER DRIFT CHAMB

' timFngT uts?1A ORB COUNTER AND >ID COUNTER IN TIME WITH BE AM - GATE (20 ns)IF a-2 0 COUNTERS ANTI-SELECT COSMICS

$

PASS 1 MUON SAMPLE ~ 0 7 */• of data

[ Z I PASS 1 TAPE

CONSTRUCT COUNTER TRACKS

ADC/ TOC INFORMATION -*■ E,0, f OF TRACK OR GROUP OF TRACKS WITHIN 20° CONE

CONSTRUCT EVENT PARAMETERS WITH COUNTERTRACK: ^ 0 3S /s

F.// < 0 5 E vISE1 < 0.5 E vis

......CRUDE MULTfPLICITY ^NTTvFRTEX'TOT I JJSING .DRIFT-TUBES AND INNER CHAMBER^

$-^0.03V. of data sarn ie ( ~ 18 events/tape)

| SCAN 5TT GRA PH IC "dFsPLAYc : ACCEPTED HADRON SAMPLE

□

1

FIGURE 17.Block diagram of offline data reduction by pass 1 and pass 2 filters.

- 3 8 -

energy i s made. A b a l a n c e c u t i s a l s o made, e x c lu d in g e v e n t s which have

most o f th e energy d e p o s i t e d i n on ly one d e t e c t o r q u a d r a n t . Approximately

1.8% of th e o r i g i n a l e v e n t s a r e a c c ep ted by the hadron f i l t e r .

The muon f i l t e r r e q u i r e s a p o s s i b l e t r a c k i n the o u t e r d r i f t

chambers and a p p l i e s t im ing c u t s , S i g n a l s i n a t l e a s t one A or B co u n te r

must be in t ime w i th the beam g a t e a long w i t h a t l e a s t one s i g n a l in

D c o u n t e r s which a r e s h i e l d e d by 42 cm of i r o n . In a d d i t i o n , i f t h e r e

i s more th a n one D c o u n t e r w i th a s i g n a l , t h e t ime d i f f e r e n c e between

c o u n t e r s i s used to r e j e c t cosmic r a y s . Approx im ate ly 0.7% of the o r i ­

g i n a l e v e n t s pass t h e s e c u t s , so t h a t the o v e r a l l pass 1 o u t p u t i s 2.5%

of the raw d a t a .

The p a s s 2 f i l t e r i s much more r e f i n e d . The energy c a l c u l a t i o n

d e s c r i b e d in S e c t io n 3 .3 a i s u s e d , and the t o t a l energy, r e q u i r e d to

be > 35% of: the c e n t e r of mass energy . The e v e n t s must a l s o be ba lanced

to w i t h i n 50% of Ev:j s ' In a d d i t i o n , an a n g l e -d e p e n d e n t c u t on th e energy

d e p o s i t e d i n the l a t t e r p a r t o f t h e c a l o r i m e t e r (K in F ig u re 6) i s made

+ -fo r h a d r o n ic e v e n t s . Th i s c u t i s used to d i s t i n g u i s h Bhabhas and e e y y t

The d r i f t tu b e s and the i n n e r chambers a r e used to make a c u t on the

l o n g i t u d i n a l v e r t e x p o s i t i o n and a m u l t i p l i c i t y c u t which a l s o reduce s

the Bhabha background. The end r e s u l t o f t h e s e c u t s i s a sample of

hadron c a n d i d a t e s t h a t i s t y p i c a l l y 0.03% o f t h e o r i g i n a l raw d a t a sample.

The f i n a l s e l e c t i o n o f h a d r o n - , muon-, and l a r g e a n g l e Bhabha

e v e n t s i s made by scann ing th e c a n d i d a t e s , s e l e c t e d i n the p a s s 2, on a

v id e o s c r e e n . This in done by p h y s i c i s t s w i t h th e use of an i n t e r a c t i v e

d i s p l a y program. The program can p l o t th e d e t e c t o r components and

ene rgy d e p o s i t e d i n d i f f e r e n t p r o j e c t i o n s and m a g n i f i c a t i o n s , F i t s

th rough t h e h i t s i n t h e d r i f t chambers and th e c o u n t e r s can be made o n - l i n e .

The c o u n t e r t r a c k s can be r o t a t e d i n space t o s tu d y th e e v e n t shape .

- 3 9 -

A l a r g e p a r t o f the a n a l y s i s e f f o r t f o r the MARK J d e t e c t o r i s

devo ted to th e development and use o f Monte Car lo programs.

T h i s s im u l a t i o n o f e v e n t s p ro cee d s i n t h r e e s t e p s ,

1. Event g e n e r a t i o n

2. D e te c to r s i m u l a t i o n

3. Event coding

The even t g e n e r a t o r s produce s im u l a t e d e v e n t s f o r a wide v a r i e t y

of e e r e a c t i o n s . The momenta, m asses , c h a r g e s , and th e s p a t i a l

d i s t r i b u t i o n of t h e f i n a l s t a t e p a r t i c l e s a r e g e n e ra te d a c c o rd in g to the

p h y s i c s h y p o th e s i s a p p r o p r i a t e to each p r o c e s s .

“f- ***Hadron p r o d u c t i o n by e e a n n i h i l a t i o n

e) Monte Carlo Simulation

i s t r e a t e d in t h e framework o f quantum chromodynamics (QCD), where the

f i n a l s t a t e hadrons a r e viewed a s com posi te p a r t i c l e s made up of quarks

(and a n t i q u a r k s ) bound by a f o r c e m e d ia te d by g luons . P ro c e s s (1)

p ro c e e d s th rough th e p r o d u c t i o n of a q u a r k - a n t i q u a r k (qq) p a i r , accompanied

by th e p o s s i b l e f i n a l b t a t e r a d i a t i o n o f one o r two g lu ons (denoted by

g o r gg) o r i n r a r e c a s e s by t h e p r o d u c t i o n of an a d d i t i o n a l qq p a i r .

The quarks and g luons th e n f r agm e n t , meaning t h a t th e y p u l l a d d i t i o n a l

qq p a i r s from th e sea w i th l i m i t e d P t w i th r e s p e c t t o the quark or gluon

d i r e c t i o n s , forming j e t s of h ad ro n s . R e a c t io n (1) th u s i n c l u d e s the

f o l l o w i n g s u b - p r o c e s s e s :

+ ~e e -*• hadrons (1)

4- — —e e -»■ qq -v hadrons ( l a )

+ - - e e •+■ qqg -> hadrons ( lb )+ - — e e -> qqgg hadrons ( l c )+ — - —

e e •+ qqqq hadrons (Id)

As an example, F ig u re 18 shows a qqg f i n a l s t a t e , accompanied by

r a d i a t i o n of an i n i t i a l s t a t e pho ton , which l e a d s to m u l t i - j e t s .

FIGURE 18.Gluon bremsstrahlung from the flt>al stoto of e+e~ annihilation into quark anttquark pairs.

For the MARK-J s e a rc h f o r th e e x i s t e n c e o f new heavy quark f l a v o r s

such a s th e top quark t , the r e a c t i o n

+ -e e -> t t -> hadrons ( l e )

i s s im u la te d a s a s p e c i a l car.e of p roces s ( l a - l d )

P a i r p ro d u c t io n of th e charged l e p t o n s , th rough the r e a c t i o n s

+ - + -e e e e (2)

+ - + -e e •> y y (3)•j* >■ "j- •»

e e ■> t t -> hadrons and l e p t o n s (4)

i s a l s o s im u l a t e d . The a n a l y s i s of computer g e n e r a t e d f i n a l s t a t e s f o r

r e a c t i o n s ( 2 ) —(4) i s a major p a r t of the QED t e s t s d i s c u s s e d i n S e c t io n 4 .1 .

O the r p r o c e s s e s s im u la te d in c lu d e

e+e -► yy (5)

and t h e "two pho ton p r o c e s s e s "

+ _ + - -f _e e ■+ e e e e (6)4- — — 4* —

e e ■+ e e p m (7)+ - + —

and e e ■> e e + hadrons (8)

Event t y p e s ( l a ) - ( l e ) a r e g e n e ra te d u s i n g a s l i g h t l y m o d i f i e d

v e r s io n o f the computer program r e c e n t l y implemented by A. A l l , E. P i e t a r i n e n ,

G. Kramer, and J . W i l l r o d t ( 1 2 ] , which p r o v i d e s a d e t a i l e d model of hadron

p ro d u c t i o n by e e a n n i h i l a t i o n in t h e frawework of QCD. In g e n e r a l ,

qq p a i r s a r e produced in f r a c t i o n s p r o p o r t i o n a l to t h e s q u a r e of th e

quark c h a rg e s f o r f l a v o r s up, down, s t r a n g e , charm, and bo t tom (denoted

u, d , s , c , and b r e s p e c t i v e l y ) . The f r a g m e n t a t i o n p r o c e d u r e used to

t r a n s fo rm quarks i n t o hadrons i s s i m i l a r t o t h a t used by Feynman and

F ie l d [13 ] . The f r a g m e n ta t io n f u n c t i o n s used a r e zD(z) » (1 - z) fo r

u, d, and s qua rks and zl>(z) » c o n s t a n t f o r c and b q u a r k s , where z

r e p r e s e n t s t h e f r a c t i o n of the quark momentum c a r r i e d away by the hadron

formed a t each s t a g e of the f r a g m e n ta t i o n p r o c e s s [ see Ref . 1 3 ] .

Heavy quarks (c and b) a r e al lowed to decay weakly a c c o r d i n g to t h e u s u a l

s i x quark model [14] , and th e l i g h t quarks produced i n t h e decay sometimes

fragment i n d e p e n d e n t l y , forming a d d i t i o n a l j e t s .

Since g luon f r a g m e n ta t io n f u n c t i o n s a r e unknown, g lu ons s im p ly fragment t o

quark p a i r s which in t u r n fragment a c c o r d in g to the normal p ro c e d u re .

The qqg e v e n t s i n which hard n o n - c o l l i n e a r g lu o n s a r e r a d i a t e d ( see Fig .

18) a r e g e n e r a t e d a c c o rd in g to the p e r t u r b a t i v e QCD m a t r i x e l e m e n t s which

in c lu d e s t h e e f f e c t s of n o n -z e ro quark mass [15 ] . Even ts of t h i s type

a r e r e q u i r e d t o have a t h r u s t ( S e c t i o n 4 .3a ) l e s s than 0 .95 b e f o r e f r a g ­

m e n ta t io n in o r d e r to avo id t h e s i n g u l a r i t y f o r s o f t o r c o l l i n e a r gluon

em iss ion [1 2 ] , We have checked t h a t our r e s u l t s do not: depend s t r o n g l y

on th e v a l u e o f t h i s c u t .

Events from th e h ig h e r o r d e r QCD p r o c e s s e s qqgg and qqqq a r e t r e a t e d

in a s i m i l a r way to t h o s e from qqg. The p r i n c i p a l d i f f e r e n c e i s t h a t

i n s t e a d o f a p p l y in g the t h r u s t c u t , the r e q u i r e m e n t of a c o p l a n a r i t y

g r e a t e r t h a n 0 .05 i s imposed, where a c o p l a n a r i t y i s d e f i n e d as

This im p l ie s t h a t none of the four p a r t o n s can be s o f t and t h a t no two

a r e c o l l i n e a r . I t d o es , however, r e j e c t p l a n a r e v e n t s which a r e n o t n ea r

a s i n g u l a r i t y in the m a t r ix e lement . We have a l s o used a t t g e n e r a to r [15 ] .

which p roceeds in the same way as f o r o t h e r heavy q u a r k s > to s tudy the

e f f e c t s t h a t w i l l be u s e f u l In s e a r c h i n g fo r the top quark .

A l l o f the f i r s t fou r even t g e n e r a t o r s use a s im ple (QED) r a d i a t i v e

c o r r e c t i o n g e n e r a t i o n [16] which assumes t h a t on ly i n i t i a l s t a t e photon

e m is s io n i s im p o r ta n t and t h a t a l l o f t h e s e pho tons go a long the beam

d i r e c t i o n w i th a momentum spectrum g iv e n by the e q u i v a l e n t p h o to n - a p p r o x i -

m a t ion .

Bhabha s c a t t e r i n g , p p a i r p r o d u c t i o n , x p a i r p r o d u c t i o n and yy e v e n t s

a r e c u r r e n t l y g e n e r a t e d accord ing to lo w es t o r d e r d i s t r i b u t i o n s and

r a d i a t i v e c o r r e c t i o n s a r e ap p l i e d e x t e r n a l l y u s in g th e programs of

Berends e t a l . [20] , ( s ee S ec t io n 3 . 3 d ) . Two-photon even t g e n e r a t i o n f o r -f- ■— ■— «■ -f'

e c -► e e e e and e e -► e e p p i s done u s in g the program of Vermaseren4

[17| which i s cxac t to o rd e r a in th e c r o s s s e c t i o n .

The o u tp u t of th e Monte Carlo g e n e r a t o r s i s i n a format t h a t can be

c o n v e n i e n t l y used by th e d e t e c t o r s i m u l a t i o n program, Th is L a t t e r program

p ro c e e d s in the f o l l o w i n g way. P a r t i c l e s a r e t r a c k e d th rough the d e t e c t o r

and i n t e r s e c t i o n p o i n t s w i th coun te r and chamber p l a n e s a r e computed.

The amount of energy i n each h i t c o u n t e r i s de te rm ined from t a b l e s that*

g iv e t h e dependence on p e n e t r a t i o n d e p t h , a n g l e , and p a r t i c l e energy . Energy

and E^ is the vector energy and n^ is chosen to minimize A.

- 4 3 -

r e s o l u t i o n and l o n g i t u d i n a l shower f l u c t u a t i o n s a r e a l s o s im u la te d u s in g

t a b u l a t e d i n f o r m a t io n . The above-men tioned t a b l e s were g e n e ra te d from

the t e s t beam d a t a t a k e n w i th e l e c t r o n s and p io n s a t e n e r g i e s from 0 ,5

to 10 GeV, from e x p e r i m e n t a l c a l o r i m e t e r s t u d i e s [18] and from shower

Monte Car lo programs [19 ) .

H i t s in the d r i f t chambers and d r i f t t u b e s a r e d i g i t i z e d . The

chamber per formance i s s im u la te d i n d e t a i l i n c l u d i n g background ,

i n e f f i c i e n c y , m u l t i p l e h i t s , c r o s s t a l k and 6 - r a y s . The f u l l

chamber survey in f o r m a t i o n i s used as p rov ided on an i n p u t f i l e . The

somewhat com pl ica ted d r i f t d i s t a n c e v e r s u s d r i f t t im e f u n c t i o n i s a l s o

rep roduced [ S e c t io n 3 . 2 c ) .

F i n a l l y the c o u n t e r ADC and TDC i n f o r m a t i o n i s d i g i t i z e d . P u ls e

h e i g h t s a r e c o r r e c t e d f o r a t t e n u a t i o n i n the s c i n t i l l a t o r and t im es a r e

c o r r e c t e d fo r p a r t i c l e f l i g h t t im e , s c i n t i l l a t i o n l i g h t t r a n s i t t ime and

time slewing due to v a r y i n g p u l s e h e i g h t . M u l t i p l e h i t s a r e a l s o t r e a t e d #

To summarize, t h e d e t e c t o r i s s im u la te d i n d e t a i l so t h a t Monte

Car lo even ts can be t r e a t e d i n t h e same way a s a c t u a l d a t a . To

complete t h i s p r o c e s s , t h e i n f o r m a t io n d e s c r i b e d above i s then coded i n t o

a form t h a t r esem bles t h e raw d a t a formal:. These e v e n t s a r e s t o r e d on

tape or d i s k so th e y may be read by the v a r i o u s a n a l y s i s programs. This

i s u s e f u l f o r many p u rp o s e s such as c a l c u l a t i o n o f a c c e p ta n c e f o r a p r o ­

c e s s , computa t ion o f background, and d e t e r m i n a t i o n o f d e t e c t o r e f f e c t s

on measured q u a n t i t i e s . In p a r t i c u l a r , we use Monte C ar lo s im u l a t i o n of

the MARK J d e t e c t o r , and th e a p p r o p r i a t e even t g e n e r a t o r , t o produce

expec ted d i s t r i b u t i o n s i n v a r i a b l e s t h a t can be compared to d a t a .

- 4 4 -

d) R a d i a t i v e C o r r e c t i o n s f o r Luminos ity M oni to r ing and T e s t s of QED

The lu m in o s i ty i n the MARK J i n t e r s e c t i o n i s m on i to red by measur ing

the r a t e of Bhabha e v e n t s in the c e n t r a l A c o u n t e r s [Figure- and the

sm al l an g le l u m in o s i ty m o n i to r , d e s c r i b e d e a r l i e r . We assume t h a t a t2

p r e s e n t e n e r g i e s and smal l q the a b s o l u t e r a t e of t h e Bhabha s c a t t e r i n g

p ro c e s s i s w e l l d e s c r ib e d by QED and i t may th u s be used as an a b s o l u t e

2m on i to r . The l a r g e q Bhabha s c a t t e r i n g covered by t h e A c o u n t e r s as

d e s c r ib e d in S e c t io n 4 .1 a i s a l s o w e l l d e s c r i b e d by QED and can be used

as an independen t m on i to r . N e v e r t h e l e s s , c a r e must be be e x e r c i s e d to

t a k e p roper account of r a d i a t i v e c o r r e c t i o n s which may be as l a r g e as

20% f o r some f i n a l s t a t e c o n f i g u r a t i o n s i n our d e t e c t o r .

The. measured r a t e f o r Bhabha s c a t t e r i n g ( r e a c t i o n (2 ) ) r e c e i v e s

c o n t r i b u t i o n s from a l l o rd e r s in t h e p e r t u r b a t i o n e x p an s io n of QED.

Fur the rm ore , g iven the f i n i t e energy and p o s i t i o n r e s o l u t i o n of th e

d e t e c t o r * some e v e n t s i n which a hard photon i s r a d i a t e d

4* •• *f* ■»e e ->• e e y (9)

a r e a l s o d e t e c t e d and a t t r i b u t e d to Bhabha s c a t t e r i n g .

I t i s t h e r e f o r e n e c e s s a ry to e v a l u a t e the c o n t r i b u t i o n to the3

t o t a l Bhabha s c a t t e r i n g c r o s s s e c t i o n to o r d e r a . H igher o r d e r c o r r e c t i o n s

a r e d i f f i c u l t to compute and have no t y e t been c a l c u l a t e d e x a c t l y . F o r -3

t u n a t e l y , they a r e sm al l s i n c e the r e s u l t o f t h e a c o r r e c t i o n i s a l r e a d y

o n ly a few p e r c e n t .

The c a l c u l a t i o n s d e s c r ib e d below were f i r s t c a r r i e d o u t by Berends

and Gastmans [2 0 ] , and we use the most r e c e n t v e r s i o n o f t h e i r computer

p rogram m o d i f i e d f o r our d e t e c t o r . We w r i t e t h e c r o s s s e c t i o n fo r

Bhabha s c a t t e r i n g a s

4 5 -

do * dgpdfi dil

( 1 + <S[ 8 » <t>3)

2where daQ/dQ i s t h e low es t o r d e r (a ) c t o s s s e c t i o n and 6 r e p r e s e n t s the

3r a d i a t i v e c o r r e c t i o n t o o r d e r a . Fo llowing th e n o t a t i o n of B e rends , we

w r i t e

6 «* 6. + 5 ,b v

where 6^ i s due t o r e a l b r e m s s t r a h l u n g and r e c e i v e s c o n t r i b u t i o n s from

t h e e i g h t d iagrams in F ig u re 19a and 6 i s due t o v i r t u a l b r e m s s t r a h l u n g

which i s the c o n t r i b u t i o n o f t h e i n t e r f e r e n c e between th e low es t o r d e r

e +

( a )FIGURE 19.

( b )Radiative correction diagrams for the process e+e -> e+e'

- 4 6 -

diagrams an", the d iagrams in which one c lo se d loop occu rs (due t o v i r t u a l

pho tons , v i r t u a l e l e c t r o n - p o s i t r o n p a i r s , y y o r T T p a i r s ) shown in

F igu re 19b.

R e n o rm a l iz a t io n removes t h e u l t r a v i o l e t d iv e rg e n c e of 6v » and one

i s l e f t w i th an i n f r a r e d d iv e rg e n c e which i s e x a c t l y c a n c e l l e d by the

i n f r a r e d d iv e rg e n c e o ccu r in g i n 6^; 6 i s then f i n i t e .

A f u r t h e r c o r r e c t i o n which could have been in c lu d e d in 6 i s thev

hadron c o n t r i b u t i o n t o vacuum p o l a r i z a t i o n . I t can be th ough t of as

q u a r k - a n t i q u a r k loops o c c u r in g i n th e photon p ro p a g a to r and i s 3 im i l a r

to l e p t o n lo o p s . Those c o n t r i b u t i o n s have been c a l c u l a t e d by Berends

and Komen [16] u s in g e x p e r i m e n t a l knowledge of R, the r a t i o of t h e c ro s s

s e c t i o n f o r e e •+ hadrons t o th e c ro s s s e c t i o n o f the p o i n t - l i k e p rocess■f -• •-(- Q

e e -+ y y . At 90 w i th r e s p e c t to t h e beam a x i s the c o n t r i b u t i o n from

quark lo ops t o 6 i s of the o r d e r of +4% a t / s « 17 GeV and s lowly i n c r e a s e s

w i th energy .

1) Small Angle R a d i a t i v e C o r r e c t io n s

The r a d i a t i v e c o r r e c t i o n s f o r the sm al l a n g l e Bhabha s c a t t e r i n g r e q u i r e

c a r e f u l t r e a t m e n t s in c e th e d i f f e r e n t i a l c r o s s s e c t i o n i s s t r o n g l y peaked

in t h i s r e g io n . Ripken [22] has overcome th e t e c h n i c a l d i f f i c u l t i e s of

n u m e r i c a l com puta t ion in th e s m a l l ang le r e g io n by u s in g G auss ian i n t e ­

g r a t i o n t e c h n i q u e s , and he has a p p l i e d h i s program to the c a s e o f the

MARK-J u s i n g a m a t r ix element p rovided by Berends [16, 20) . At a ng le s

s m a l l e r t h a n 5° w i th r e s p e c t t o the beam a x i s , a l l e l e c t r o n muon and tau

loop d ia g ra m s and th e h a d ro n ic c o n t r i b u t i o n to vacuum p o l a r i z a t i o n a r e

s m a l l and a r e n e g l e c t e d .

In th e smal l a n g le l u m in o s i ty m o n i to r in g s t a t i o n s , a s d e s c r i b e d i n

S e c t io n 3 .2 b , p a i r s com pr i s ing one s m a l l s c i n t i l l a t o r and one o p p o s i t e

l a r g e s c i n t i l l a t o r d e f i n e t h e a c c e p ta n c e . The geometry o f t h e s e co u n te r s

has been i n c o rp o r a t e d i n t o the r a d i a t i v e c o r r e c t i o n s i n t h e fo l lo w in g

f a s h i o n . For th e h a rd -p h o to n p a r t o f t h e c r o s s s e c t i o n e l e c t r o n - p o s i t r o n -

photon t r i p l e t s a r e g e n e ra te d where one of the l e p t o n s i s w i t h i n th e a c c e p t ­

ance of a smal l s c i n t i l l a t o r and the o t h e r l e p t o n i s r e q u i r e d t o pass w i t h i n

t h e b o unda r ie s of t h e l a r g e s c i n t i l l a t o r d i a m e t r i c a l l y o p p o s i t e . The s o f t

photon p a r t i s i n c o rp o r a t e d a n a l y t i c a l l y . These c o r r e c t i o n s a r e very

s e n s i t i v e to the r e l a t i v e p o s i t i o n of t h e sm al l s c i n t i l l a t o r w i th r e s p e c t

t o t h e l a r g e r one. The r e s i d u a l u n c e r t a i n t y i n t h e p o s i t i o n s of the

s c i n t i l l a t o r s c o n t r i b u t e s a r e l a t i v e s y s t e m a t i c e r r o r i n t h e c a l c u l a t i o n of

6 of abou t 30%. S ince t h e v a l u e of <5 i s -8%, t h e r a d i a t i v e c o r r e c t i o n s

c o n t r i b u t e an e r r o r of 2.5% to t h e t o t a l l u m in o s i ty measured i n th e smal l

a n g le m o n i to r .

i i ) Large Angle R a d i a t i v e C o r r e c t i o n s

For l a r g e ang le Bhabha s c a t t e r i n g th e phase space f o r r e a l brems­

s t r a h l u n g can be e x p e r i m e n t a l l y c h a r a c t e r i z e d by two s im p le b o u n d a r ie s :

: an energy t h r e s h o l d f o r t h e ou tgo ing

e l e c t r o n and p o s i t r o n

£ 5 a l i m i t on the a n g l e i n space between th e e l e c t r o n

d i r e c t i o n and th e d i r e c t i o n a t 180° t o th e p o s i t r o n

d i r e c t i o n ( a c o l l i n e a r i t y c u t ) .

F ig u re 20 shows 6' p l o t t e d as a f u n c t i o n of 0 over t h e A c o u n t e r accep tanc e

a t / a w 27 .4 GeV f o r v a r i o u s combinations of t h e c u t s .

- 47 -

RADIATIVE CORRECTIONSa) £* 50° Etht3 GeVb) |* 50°Eth*4.5GeVc) g* 20° Eth * 3 GeV

-------- 1_-- ------ L_.----- --L__ 1__L60 90 120 150 167 6 180 Q j-0-j

FIGURE 20.Radiative corrections 6 as a function of the scattering angle 0 for different acceptance cuts.

The c u t s used to d e f i n e the sample f o r the MARK J l u m i n o s i t y measure­

ment a t l a r g e ang les a r e :

The energy t h r e s h o l d c u t i s chosen to be w e l l below t h e t a l l

of t h e energy r e s o l u t i o n curve w i th i t s r . m . s . w id th of Z 10% so t h a t the

r e s o l u t i o n c o r r e c t i o n i s n o t v e ry s e n s i t i v e t o t h i s c u t .

With t h e knowledge o f 6 one mav i n t e g r a t e the d i f f e r e n t i a l c r o s s

s e c t i o n o ver th e d e t e c t o r acc ep tan c e to f i n d t h e Bhabha r a t e expec ted in

t h e c e n t r a l d e t e c t o r . Knowledge of t h e ac c e p ta n c e a t t h e end o f the

c o u n t e r s i s e s p e c i a l l y im p o r ta n t s in c e the Bhabha c r o s s s e c t i o n i s s t r o n g l y

peaked a t s m a l l a n g l e s and most of the c o n t r i b u t i o n to t h e t o t a l r a t e comes

from t h e end r e g i o n o f t h e c o u n t e r s . Near the edge of t h e a c c e p ta n c e the

£ - 50°

- 4 9 -

EFFICIEHCY FUNCTION Al THE ENO OF A COUNTER

POSITION FROM CENTER OF COUNTER imm)

FIGURE 21.Efficiency function at the end of the A shower counters.

r a d i a t i v e c o r r e c t i o n s become l a r g e and n e g a t i v e as more photons of lowet

energy can cause one of the ou tgo ing e l e c t r o n s to r e c o i l o u t s i d e the

c o u n te r l i m i t s . Because of t h e sp read of t h e e l e c t r o m a g n e t i c shower and

because of back s c a t t e r e d showers from n e ig h b o r in g c o u n t e r s , t h e a c c e p ta n c e

does n o t drop s h a r p l y a t the end of t h e A c o u n t e r s b u t shows a t a i l beyond

th e g e o m e t r i c a l end of the c o u n t e r s ( s e e F ig u re 21). The e f f i c i e n c y of the

A c o u n t e r s nea r t h e i r ends i s computed u s in g th e Mojjte Car lo s i m u l a t i o n

d e s c r i b e d i n s e c t i o n 3 . 3 c , and the s p e c i a l i z e d Monte Car lo program EGS

( E l e c t r o n Gamma Shower) developed a t SLAC which p rov ided d e t a i l e d in fo rm ­

a t i o n on e l e c t r o m a g n e t i c showers [21 ] .

The r e s u l t s o f t h e c a l c u l a t i o n o f t h e c r o s s s e c t i o n over th e A c o u n t e r s ,

i n c l u d i n g the r a d i a t i v e c o r r e c t i o n s , a r e shown i n F ig u r e 22.

10 12 14 16 18 20 22 24 26 28 30 32 34 36 38

ifS GeV

FIGURE 22.> *4* «— *f*The calculated cross section e e -*■ e e integrated over the solid angle covered by the A shower counters,

We f i n d t h a t t h e l u m in o s i ty measurement w i th t h e c e n t r a l d e t e c t o r a g re e s

w i t h i n ^ 3Z w i th t h e measurement made with th e smal l a n g le l u m i n o s i t y c o u n t e r s

( s e e F ig u r e 23 ) .

“i----- 1----- r

0 . 1 -

~ oo O

«► ot

IT

- 0 . 1 -

3 0 . 0

-J---------- 1----------1---------- 1_ --- 1-------- 1--------1________ I________ I________ L.

3 0 . 5 3 1 . 0

" < s ( G e V )

FIGURE 2 3 .Luminosity measured with the central detector and with the luminosity monitor (Lq ) during energy scan.

- 5 2 -

T es t of Quantum E lec t ro d y n a m ic s and o f U n i v e r s a l i t y f o r Charged Lep tons

There have been many e xpe r im en t s t e s t i n g quan tu ra -e lec t rodynam ics

(QED) w i th e l e c t r o n s , muons and pho tons a t e l e c t r o n - p o s i t r o n s t o r a g e

r i n g s . Notab le ex p e r im e n t s [23] were done by A l l e s - B o r e l l i e t a l . ,

Newman e t a l . , August in e t a l . , O’N e i l l e t a l . , and by our group a t

PETRA [24] up t o a c e n t e r o f mass ene rgy o f 17 GeV. For a comprehensive

rev iew o f QED work, see Brodsky and D r e l l [25 ] . Much has been l e a rn e d

about the p r o p e r t i e s of t h e heavy l e p t o n t a u s in c e t h e o r i g i n a l s e a rc h

•f -began a t ADONE on e + e ■+ ye + . . . [26] . The d i s c o v e r y of the t

l e p t o n a t SLAC [27] and i t s s ubse quen t c o n f i r m a t i o n a t DESY [28] has

i n s p i r e d f u r t h e r s t u d i e s . We know i t i s a s p i n 1/2 p a r t i c l e which

decays weakly [29] and whose p r o p e r t i e s a r e v e ry s i m i l a r t o the muon.

In t h i s exper im en t we s tu d y the r e a c t i o n s e ■+ e •+ % + SL f o r

a l l t h e known charged l e p t o n s (& « e , y , r ) by measur ing th e dependence of

the c r o s s s e c t i o n on c e n t e r o f mass ene rgy o r s c a t t e r i n g a n g l e over a

wide ra n g e of PETRA e n e r g i e s , These measurements e n a b le u s to compare

th e d a t a w i th p r e d i c t i o n s of quantum e l e c t r o d y n a m i c s , t o t e s t the

u n i v e r s a l i t y o f t h e s e l e p t o n s a t v e ry s m a l l d i s t a n c e s , and t o s e t a

l i m i t on t h e ch a rg e r a d i u s of t h e s e p a r t i c l e s . Up to t h e p r e s e n t t ime

t h e r e a c t i o n s ;

4) PHYSICS RESULTS

- 5 3 -

+ - + ->e + e ■+ e + e (Bhabha s c a t t e r i n g ) (2)

e + e ■+ u + u (3)

--+■ ( h ' s o r e) + v ’ s

e + e -> t + t (4)

-->■ n + v ' s

have been measured a t t h e c e n t e r o f mass e n e r g i e s /s~ =■ 12, 13, 17, 22, 2 7 .4 ,

30 and 31 .6 GeV.

a) Bhabha S c a t t e r i n g

The Bhabha e v e n t s a r e i d e n t i f i e d by r e q u i r i n g two b a c k - t o -b a c k

showers i n the A, B and C c o u n t e r s which a r e c o l l i n e a r to w i t h i n 20°

i n <f> and 0 and w i th a measured t o t a l shower energy g r e a t e r than 1/3 of the

i n c i d e n t beam energy . Photons e m i t t e d c l o s e to e i t h e r e l e c t r o n a r e in c lu d ed

in t h e e l e c t r o n momentum. From th e measurement of th e a c o l l i n e a r i t y ang le

AO, and the a c o p l a n a r i t y a n g le A<£, we ob s e rv e t h a t most o f the ev en t s a r e in

th e r e g i o n £B < 4° , A<J> < 4° . Because t h e r e a r e few e v e n t s nea r the 20° c u t s in

A0 we conc lude t h a t t h e background t o Bhabha s c a t t e r i n g i s n e g l i g i b l e .

To e l i m i n a t e most background from hadron j e t s , the energy in the

K c o u n t e r s was r e q u i r e d to be l e s s th a n 7% of the t o t a l energy . Because

t h e QED t e s t i s most s e n s i t i v e to background i n the l a r g e ang le r e g io n ,

a l l e v e n t s having 6 l a r g e r than 60° were scanned on g r a p h ic d i s p l a y s

which showed the d i s t r i b u t i o n o f c o u n te r h i t s . On the b a s i s of a

Monte Carlo s tudy of hadron e v e n t s , we conclude t h a t the background

from t h i s s ou rce i s l e s s th a n 1% of t h e e v e n t s . As ment ioned above,

t h e acc ep tan c e f o r e e -+ e e was computed u s in g Monte C ar lo t e c h n iq u e s

and i s d e f in e d by the geometry of the f i r s t shower c o u n t e r a r r a y A.

Roth energy and acc ep tan c e l o s s e s in t h e c o r n e r s were found to be sm al l .

The f i r s t o rde r QED photon p r o p a g a t o r produces an s ^ dependence

in the e e ->• e e c r o s s s e c t io n - Thus when r a d i a t i v e c o r r e c t i o n s have been taken

in t o account in the d a t a , the q u a n t i t y s vs cosO should be independen t

of s . This d i s t r i b u t i o n i s p l o t t e d fo r the d a t a a t / s =» 13, 17 and

27.4 Gev in F igure 24. E x c e l l e n t agreement w i th QED p r e d i c t i o n s i s

seen , To e x p re s s t h i s agreement a n a l y t i c a l l y , we compare our d a t a w i th

the QED c r o s s s e c t i o n in th e fo l low ing form ( s in c e charge i s no t d i s ­

t i n g u i s h e d he re ) [30] :

I 2 2 O 0 ' 4 4 0„ £ « - | _ {.a------- J L |F J + _ a — R e ( F s F T * ) + j

q q s s

- 5 4 -

+ ^ 4 —- | F^ | 2+ Re(F'F *) + 51— J 3—! FT j 2 > (1+C(9)},q q s

where

Ffl - 1 + q2/(q2 “ * s±2 )

is the form factor of the spacelike photon,

FIGURE 2 4 .

T he d e fe re n tia l cross s e c tio n s ~ ~ ' fo r e+e_ -»■ e *e - a t J s o f 13 , 1 7 , and 2 7 .4 G e V .dcose?

2 2 '2 ? i s the form f a c t o r o f t h e t i m e l i k e p h o to n , q - s cos q ** ~"s 8*n

A i s t h e c u t - o f f p a r a m e te r i n t h e m od i f ied p ho ton -pvopaga to r

model [31] and G(0) i s th e r a d i a t i v e c o r r e c t i o n te rm a s a f u n c t i o n of 0 .•U mm

The r a d i a t i v e c o r r e c t i o n to t h -3 e e e l a s t i c s c a t t e r i n g p ro ces s was c a l c u l a t e d

u s in g th e program o f Berends f o r t h e s e p a r t i c u l a r ev e n t s e l e c t i o n c r i t e r i a [20] .

In o rd e r to e s t a b l i s h lower l i m i t s on the c u t - o f f p a r a m e te r s amm

Monte Car lo program was used to g e n e r a t e e e p a i r s which were then t r a c e d

th rough the d e t e c t o r w i th the i n c l u s i o n of measured 0 , <j) r e s o l u t i o n s .

A x2 f i t to a l l o f t h e 13, 17 and 27.4 GeV d a t a i s t h e n made u s in g the

Monte Car lo g e n e r a t e d a n g u l a r d i s t r i b u t i o n . The n o r m a l i z a t i o n i s t r e a t e d

in two ways; (1) t h e t o t a l number o f Monte Car lo e v e n t s in the r e g io n

0 .9 0 < cosO < 0 .98 was s e t equa l t o the t o t a l number of measured e v e n t s

2i n the same r e g i o n , ( 2) the minlmum-x f o r the e n t i r e d a t a sample d e t e r ­

mined th e n o r m a l i z a t i o n . The two methods ag re e w i th each o t h e r to

w i t h i n 3% and g iv e e s s e n t i a l l y the same r e s u l t i n t h e c u t - o f f p a ram ete r A.

The lower l i m i t s of A a t 95% co n f id e n ce l e v e l under v a r i o u s assum pt ions

a r e shown i n Tab le I, The JADE and PLUTO groups have al so- ana lyzed t h e i r QED

r e a c t i o n s and have o b t a in e d s i m i l a r c o n c l u s i o n s w i th r e g a r d t o the v a l i d i t y of

QED a t em a i l d i s t a n c e s , ( s ee s e c t i o n 4 . 4 ) .

TABLE ICut-off parameters In GeV for photon form factors from Bhabha scattering.

A

21 ________ 9

2 , 2q

2

1 + ^ — 2 . 2

q - A

As 5 2 5 5

a t 6 0 5 2

A s = A T6 5 6 4

k) Muon and Tau P a i r P ro d u c t i o n [32]

The MARK J d e t e c t o r i s de s ig n ed to d i s t i n g u i s h muons from e l e c t r o n s and

hadrons and t o d i s t i n g u i s h b a c k - t o - b a c k muon p a i r s from cosmic ray

muons. Muon i d e n t i f i c a t i o n i s a l s o a id ed by th e short, decay p a t h a l low ed

to hadrons b e f o r e r e a c h i n g the shower c o u n t e r s , J.n a d d i t i o n to the

c u t s d e s c r ib e d i n S e c t i o n 3 .3 b , s i n g l e muons a r e i d e n t i f i e d a s p a r t i c l e s

which:

• 58 -

i ) a r e r e c o n s t r u c t e d i n the i n n e r d r i f t chambers to come from the

i n t e r act. ion r e g io n ;

i i ) l e a v e minimum i o n i z i n g p u l s e h e i g h t s i n th e A, B, C, K, and

D c o u n t e r s , a t o t a l of seven l a y e r s ;

l i l ) l e a v e a t r a c k i n t h e o u t e r d r i f t chambers (P) and thus

f a l l i n t o an a n g u l a r range 45° < 9 < 135°.u

In a d d i t i o n back- to-be .ck muon p a i r s from r e a c t i o n ( 3 ) a r e

d i s t i n g u i s h e d from cosmic r a y s by the re q u i re m e n t t h a t :

i) the D counter timing signals are coincident with one

another (and not relatively off time as in the case for

cosmic rays traversing the detector),

ii) the muons should be colllnear and coplanar, and they should

pass through the intersection region.

A Monte Car lo s tu d y shows t h a t t h e u p a c c e p t a n c e , which i s

dominated by th e g e o m e t r i c a l a c c e p ta n c e of t h e P d r i f t chambers, i s

41% t 3% independen t of beam energy .

Tau l e p t o n s from r e a c t i o n (4) a r e i d e n t i f i e d by d e t e c t i n g y -hadron

and p - e l e c t r o n f i n a l s t a t e s . The c r o s s s e c t i o n i s de te rmined u s in g

th e known b ran ch in g r a t i o o f t + p vv (16%) and t > (e , hadron

o r m u l t i h a d r o n s ) + v (84%) [29J . The muons, had rons and e l e c t r o n s a r e

I d e n t i f i e d a s d e s c r i b e d p r e v i o u s l y , '.'he t o t a l d e p o s i t e d energy of

h adrons (or e l e c t r o n s ) i s r e q u i r e d to be g r e a t e r than 2 GeV.

The m a jo r background to r e a c t i o n (4) i s t h e two-photon p r o c e s s :

+ e -> e+ + e + p + p (7)

This process becomes important at high energies since the total cross

i n c o n t r a s t t o r e a c t i o n ( 3 ) , t h e r a t e f o r which f a l l s a s l / s . The

observed c r o s s s e c t i o n f o r the two-photon p r o c e s s i s su p p re s se d by t

t h e muons and by energy and a n g l e c u t s on t h e e l e c t r o n s , b u t r a t e s

of t h e a c c e p te d e v e n t s remain s i g n i f i c a n t .

In F ig u r e 25 we show the c a l c u l a t e d c r o s s s e c t i o n i n our d e t e c t o r

when th e obse rved p a r t i c l e s a r e

(a) two y ' s o n ly ,

(b) o n ly one y and one e and,

(c) two y ' s and one e .

The c r o s s s e c t i o n s f o r each o f th e s e c o n f i g u r a t i o n s were computed u s in g

the Monte Car lo i n t e g r a t i o n program of Vermaseren [1 7 ] . The com puta t ions

were compared to t h e c r o s s s e c t i o n s measured f o r r e a c t i o n (7) u s in g the

f o l l o w i n g c u t s :

168° > 0 > 12° E > 2 GeV— A - c* •*-

The measured c r o s s s e c t i o n s , a l s o shown i n F ig u re 25, a g ree w e l l w i th

th e c a l c u l a t i o n s i n a l l c a s e s .

3f a c t o r ^10 r e l a t i v e t o t h e t o t a l c r o s s s e c t i o n by momentum c u t s on

135° > 0 > 4 5 °- ^ -

> 1 .5 GeV ( f i r s t muon)

147° > 6 > 3 3 °— 11 r> — PL > 0 . 8 GeV (second inuon)- y2

y s G e V

F I G U R E 25.The observed cross sections of e+ + e " -+ e+ + e~ + n + + ju~ in our detector as functions of /s when the observed particles are:a, two n ’sb, one n and o n e 0c, two /A and one e

The solid lines are Monte Carlo calculations of the yield from two photon diagrams and the points are the measurements,

■ 61 ■

The cross section for case (a) above is much larger than that for

the process4 . - •— + -e + e -> t + t -* y + M + 4v,

*|* ■>>

and the y y events from the two processes are hard to distinguish.

We therefore exclude case ( a ) from the sample of t t candidates.

In case (b) the electron from the two-photon process Is strongly peakeddo

in the small angle region. Typically, ^cosf"")' decreases by two orders

of magnitude from cosO « 0.98 to 0.80. Furthermore, the observed muons

and electrons tend to be coplanar because of conservation of transverse

momentum. By requiring 30° < 6e < 150° for the tt sample, and by

requiring that the final state ye be colliaear within 30°, we were able to_3

reduce the two-photon contribution to a negligible level (<10 picobarns).

The rate for case (c) is small and can be readily separated from the t events,

The fact that the y-hadron events produced by reaction (4) in our

energy region are almost collinear can also be used to distinguish

reaction (4) from y-hadron events produced by the seml-leptonic decay

of particles with c(charm) or b(bottom) quantum number, In the latter cases

the muon is accompanied by hadrons emitted close to the muon direction.

The measured muon momentum and hadron energy for the t t candidates

is in agreement with calculations based on the known decay properties

of the t lepton [29 ] .

The acceptance is calculated using a Monte Carlo method to generate

t t production from reaction (4) including radiative corrections.

We obtain a detection efficiency of ^ 10% for r pairs at various

energies, when requiring one decay muon to be detected in association

with a single electron, or one or more hadrons.

4. _ + —The resultant e e -> y y and t t cross sections as a function

of s are plotted in Figures 26 and 27 together with the QED prediction.

-62-

FIGURE 26.

Observed cross section f o r the reaction

e*o" -■ /j* n ~ compared to prodictions of QF.D.

-63-

FIGURE 27,

Observed cross section for the reaction4 •— 4* -o e -» r r compared to predictions o f QED.

2 2 2 We see that from q » s » 169 to q *> 999 GeV the data agree well with

the predictions of QED for the production of a pair of pol.nt~.like

particles. In particular, Figure 27 represents the first evidence

chat the t lepton is a point-like particle over a large range of q ,

and demonstrates that it belongs in the same family as the electron

and muon. To parametrize the maximum permissible size (radius) of

the particles, we use a form factor:

14 X

By comparing our data with the cross sections including this form factor

we find lower limits on the cut off parameters, at the 95% confidence

level, summarized in Table II,

TABLE II

Cut-off parameters in GeV f o r e ' i e ~ r / u + / J ~ a n d r + r ~ ~ production using leptonic form factors.

1 electron muon tau

A 95 114 69

A+74 116 118

Thus, from Heisenberg’s Uncertainty Principle, all the known

charged leptons are point-like particles in their electromagnetic

*-1 fiinteractions, with characteristic radii < 2 x 1CT cm,

- 6 5 -

4.2 Hadronic Final States

a) Hadron Identification

As described in section 3.3, the final selection for hadrons is

made by scanning the events on an interactive graphics system after a

preselection which includes energy and momentum balance cuts. In

this scanning, hits observed in the drift tubes and in the drift chambers

allow an easy determination of the event vertex. Thus beam gas events

which do not come from the interaction region are readily recognized.

The charged multiplicity observed in the drift tubes and the shower

envelope in the counters is used to reject events of electromagnetic

origin. For events which have low multiplicity both in the tubes and

the counters, we require that a minimum fraction of the total energy

is deposited in the hadron calorimeter (K in Figure 6) to further d is­

criminate against purely electromagnetic final states,

The energy spectrum of the events passing the cuts is shown in Figure 28.

For the analysis of hadronic final states we employed an additional energy cut

of Evis > 0.5/s for measurement of total cross section (Section 4.2b), for most

of the thrust analysis (Section 4.3a) and the study of inclusive muons in hadron

events (Section 4.3c). This additional cut also reduces the contamination from

beam-gas events, from two-photon processes [33] and e e ->• r T events which

yield hadrons in the final state [34].

For reasons discussed in Section 4.3d we employed an even more restrictive

cut of Ev ^g > 0.7/s for study of gluon effects in thrust distributions (Section

4.3a), for jet analysis using Fox-Wolfram moments (Section 4.3b), for the

discovery of 3-jet events (Section 4.3d) and determination of the strong coupling

constant a (Section 4.3e). Both of these cuts are Indicated by arrows in

Figure 28,

E n e r g y S p e c t r u m

FIGURE 28.

Energy distribution of hadron events satisfying the cuts described in Section 4.2a.

-99*

k) Total Hadronic Cross Section [35, 36, 37].

+ -The total cross section for e e hadrons was measured over a wide

range of center of mass energies from 12 to 31.6 GeV, including results

obtained by extended periods of running at a fixed beam energy and by a fine

energy scan covering the range of 29.92 to 31.46 GeV, The results are

expressed in terms of R:

4. *4- — *4* —R « a (e e~ -+• hadrons)/a (e e -> u M ) •

In the naive quark-parton model, the cross section for the hadron production

process is simply given by the sum over flavors of the polnt-like qq pair

cross sections. Using this picture with spin 1/2 massless quarks, and with

three colors gives

R » 3 I e2 , qq M

where e^ is the charge of the quark with flavor q. Considering the

five known quark flavors (u, d, s, c and b), and correcting the naive

model for gluon emission as predicted by QCD, we expect R - 4, over

the entire PETRA energy range, with only a slight decrease in R with

increasing beam energy.

The MARK J results for R are shown in Figure 29 along with the

QCD predictions. The data consist of a total of 1812 hadron events

corresponding to 3.5pb \ The results are summarized in Table III.

Figure 29 shows that the data agree with the QCD predictions

for five quark flavors (represented by the lower dashed line), and

that there is no sign up to 31.6 GeV of a threshold in the hadron

continuum corresponding to a new heavy quark of charge 2/3 such as

the top quark (the upper line).

! i i .. s i i I ' .....r ....

w ith t

x ■

—T I

t I t f i S t

—

-u d s c b i i

-

a n d Q C D co rre c tio n s

_

I i 1 f L 1 I I \0 4 8 1 2 1 6 2 0 2 U 2 8 3 2 3 6 4 0

"Vs (G e V )FIGURE 29.

The tota! restive hadronic cross section R = (e+e~ -*■ hadrons} / <7(e+e— -> ) at at! energies by thisexperiment. Note that the point at 27.5 GeV corresponds to data taken over the range of

27.4 to 27.7 GeV, and the point at 30.7 GeV represents the energy scan from 23.9 to 31.5 GeV.

- 69-

TABLE lil

Results of R measurement. The errors are statistical only,

/"s'

(GeV) R-t''’ R (statistical)

12.0 4.03 i 0.28

13.0 4.1. i 0.5

17.0 4.4 ± 0.6

22.0 4.7 0.7

27.57 ; 3.8 i 0.3

30.0 4.2 0.3

29.r 31.46 4.33 A 0.17

31.6 4.0 + 0.5

- combination o£ 27.4 and 27.7 GeV data

The experimental R-values in Figure 29 have been corrected Cor

initial-state radiative corrections (AR « -0.3), for contamination of

the sample by hadronlc events produced by the two photon process

e e ->- e e 4- hadrons (AR < -0.1), and for the contribution of

•f* *- *4* *-e e ■■>• t t hadrons 4- leptons (AR typically « -0.3). In addition

to the statistical errors shown, there is an additional systematic

uncertainty due to model dependence of the acceptance of 10%. The

accuracy in evaluating the contributions of the two photon and tau-

pair contributions to the hadronic event sample is limited by the lack

of detailed experimental data on the high energy, high m u ltiplicity

states arising from these sources.

toponium system should form one or more bound states, with the number

of such states depending on the shape of the binding potential [35 ] .

t ii

Interpretation of the vector mesons p, oj, <j>> J, t|/', T, T , and T ,

as nonrelativistlc qq bound states, or "quarkonla" leads to the

prediction that the gap between the lowest bound state and the continuum

I s probably ^ 1 GeV, and very likely < 2 GeV.

In order to check for the existence of tt bound states lying below

3 1 . 6 Gev, the energy scan mentioned earlier was performed in 20 MeV

center of mass energy steps (matching the r.m.s. energy spread of

PETRA), with an average of ^Snb"*'^ per point. The overall hadron event

sample for the scan consists of 807 hadronic events corresponding to

a time-integrated luminosity of 1 9 4 5 nb The results of the scan are

Rth a d r o n s

In addition to the tt contribution to the hadronic continuum, the

30.00 31.00

FIGURE 30.

R values measured during the energy scan between 29.9 and 31.5 GeV. The line represents the predictions of QCD.

shown in Figure 30, along with the results obtained earlier at 30.0

and 31.6 GeV. The figure shows that the data are entirely consistent

with the predictions of QCD for u, d, s, c and b quarks, that is, with

a constant value of R over the whole range. No single point lies > 3a

above the QCD line, and there is no indication of an upward slope

with increasing energy signaling the onset of a new contribution to

the continuum. The value of R averaged over the energy range of the

scan is 4.33 ± 0.17.

In order to set a quantitative upper bound on the possible production

of a narrow resonance, the data in Figure 30 were fitted by a constant

plus a gaussian:

- 71 -

where R^ represents the non-resonant continuum, M is the mass of the

resonance, A is the r.m.s. machine energy width, and R is the peak w v

value- of the resonant contribution. The largest value of R consistentv

with the data was determined by trying fits with M, the center of the

gaussian, fixed at all the center of mass energies at which data were

taken. The largeeit value of Rv was obtained at 31.32 GeV, corresponding

to an upper limit on the resonance strength

* v ov (w)dw, where w » /s ,

of 33 MeV-nb at the 90% confidence level. Using the relation between

•j* Mthe resonance strength, the width into e e (ree) » the hadronic width (r^),

-72-

the total width (I'), and the hadronic branching ratio (B 5 r /T) :h h

o r r i,, _ 3i r_________ e e j i ______V M 2 (w~M) 2 + r2/4

we obtained

B. r <1.3 KeV (90% C.L.). h ee

This upper limit excludes the production of a vector particle consisting

of a qq bound state where the quark has charge 2/3. On the basis of the

meson ground states p, w, <j>, J and T, as is predicted by duality argu­

ments [3b], one expects F ~ 5 KeV for the lowest mass meson in the

toponlum family. Effects due to radiative corrections and the energy

spread of the machine which Influence the shape of the cross section have

been taken into account in this analysis. Our results are in good agreement

with results obtained by different methods from other PETRA groups, JADE, PLUTO

and TASSO. (See section 4,4).

4*3 Jet Analysis

a) Thrust Distributions

Data at lower energies from SPEAR [38] have shown that the final

+ -state hadrons from the process e e -► hadrons are predominantly collimated

into two back-to-back ’'jcl'V It? agreement with the expectations of simple

models in which the tlme-llke photon materializes Initially into a quark

antiquark pair. It is thus necessary to develop kinematic quantities

which describe the jet-like nature of the MARK-J hadronic events.

experimental fact that [■ ia approximately constant for the vectoree q

spatial distribution of the energy deposited in the detector. For each

■*1counter hit, a vector E (the energy flow) Is constructed, whose direction

is given by the position of the signal in the counter, and whose

magnitude is given by the corresponding deposited energy. A parameter

thrust (T) is defined as [37]

T - m a x £ | E :J/ | / E v 1 s

A ** Awhere E , , is the parallel component of E along a given axis, and the

maximum is found by varying the direction of this axis, and where the

sums are taken over all counter hits. The resultant direction is thus

the direction along which the projected energy flow is maximized.

For events In which the spatial distribution of energy is isotropic,

T is expected to approach 0.5. This would be the situation if, for

example, the virtual photon materializes into two very heavy quarks, each

with a mass close to the beam energy. Such quarks would be

produced almost at rest. On the other hand, pairs of light quarks would

move at high speed and the Lorentz boost of their hadronic fragmentation

products would result in the hadrons being produced in narrow jets

collimated around the initial quark directions. Higher beam energies

would result in narrower jets, so that T should approach the value 1.

Thus, thrust measurements can be used as a sensitive method to detect

the presence of a new threshold due to new heavy quarks.

These expectations are illustrated qualitatively i.i Figure 31 in

which the thrust distribution expected just below and just above the

-73 •

A jet. analysis of the hadronic events has been devised using the

- 7 4 -

threshold for production ot a new heavy quark is shown. Production of

a new heavy quark would also result in lowering the average T as the

energy is raised and the threshold is passed.

The normalized thrust distributions — ~ ; for 13, 17, 22, and the

combination of 27.4 and 27.7 GeV data (labelled 27 GeV combined) are

shown in Figures 32 p,-d along with the Monte Carlo predictions of a

quark-parton model with u, d, s, c, and b quarks and no gluon emission.

NEW QUARK FLAVOR

just after threshold

FIGURE 31.

A ske tch s h o w in g th e q u a lita t iv e change in the th ru s t d is tr ib u t io n expected w hen the energy is increased and th e th re s h o ld fo r p ro d u c tio n o f a new q u a rk fla v o r is crossed.

FIGURE 32.

Thrust distribution observed at J s , - a) 13, b) 17, c) 22. d) 27 GeV {see text). The soiid line is the quark model prediction for u, d, s, c and b quarks with no gluon emission.

(The individual distributions at 27.4 and 27.7 GeV are in agreement with

each other). As expected for production of final states with two jets of

particles, the distributions become narrower and shift towards high thrust

with increasing energy.

Figure 33 shows the normalized thrust distributions for combined

data between 29.9 and 31.6 CeV where the measured energy of the selected

events is at least 70% of /s. The curves show the Monte Carlo predictions

with and without inclusion of gluons. As can be seen, these data lend

support to the necessity of including gluons in the Monte Carlo program.

The data is also compared with a Monte Carlo calculation which includes

a charge 2/3 t quark produced as described previously. For thrust

smaller than 0,75, the QCD model with a top quark predicts 283 events.

The QCD model without top quark predicts 79. We find 68. We thus

conclude that there is no evidence for production of a new heavy quark

with charge q ® |e.

Figure 34 shows the average thrust <T> plotted at the six energies.

The solid curves are from Monte Carlo calculations which include u, d,

s, c and b quarks with gluon emission. The energy dependences of the

data are smooth and show none of the steps which would have appeared at

new quark thresholds.

Similar results are obtained by the JADE, PLUTO and TASSO collaborations

on searches for new flavor production. (See section 4.4),

-77-

1 d N

N d T $ D a t a : / s " » 3 0 G e V

Q C D

Q Q

~ Q C D * T O P ( M = U G e V )

1 0

0 . 5 0 . 6 0 . 7 0 . 8 0 . 9 1 . 0

FIGURE 33.

The thrust distribution with a 70% energy cut for 'v 30 GeV.The curves are predictions for various models as described in the text.

- 78 -

1 2 1 8 2 4 3 0

I ' s ( G e V )

FIGURE 34.

Averaye value of thrust as a function of / s together with the QCD prediction (solid line). The values expected from a phase space distribution and from a QCD model with a top quark are also shown.

-79-

Another method of jet characterization has been proposed by

Fox and Wolfram. The simplest observables characterizing the three-

dimensional shape of the energy distribution in a hadronic event are

the Fox-Wolfram moments [39].

b) Jet Analysis Using Fox-Wolfram Moments

\ \ \ | B , |g --- ---- p (cosG.,), where P „ is £th Legendre polynomial

1 , 3 b J 1 s 1 J

and

|E | |E | |E | ~TT „ 2 — ------- z ~ (E * E x E. )

i,j,k (Ev t g )3 j

The H's parametrize the shape of the energy distribution by measuring

the correlation between pairs of energy flow elements in terms of

spherical harmonics. For cigar-shaped events expected from the process

e + e *»■ q + q the evan moments ^ and tend to be large, while

they take relatively low values for events broadened on one side by

the radiation of a hard non-collinear gluon (e + e q + q -f g ) . Less

significant differences are exhibited by the odd moments. The moment

involving a three-particle angular correlation, is sensitive to

the planarity of events expected from gluon bremsstrahlung.

-80-

Since all these quantities are Invariant against a aplit-up of

the particle energy vector E into separately measured components

E’ (E E' ** E.) having a small angular spread, they are well suited n n i

nfor detectors not identifying individual particle tracks. Since they

are also rotatiorally invariant, they are easily calculable and do not

involve the definition of an event axis by a maximization process.

Figures 35 and 36 show the distributions — and ~ j|j of the

combined data taken at high energies (/s > 27 GeV). They are compared

to predictions of QCD and of the quark-parton model with <Pfc> != 225 MeV/c,

where Pfc refers to the quark transverse momentum in the fragmentation process.

The experimental distributions are in excellent agreement with QCD and

clearly rule out the simple quark model at this particular <P(;> . The

same is true for the differential distribution -■ dN/drr1 , shown in

Figure 37. The predictions of the quark model for these shape para­

meters are, however, sensitive to the ‘‘•P^ chosen, so that compatibility

with the measured data can always be achieved at very high <Pt> .

An unambiguous proof for the existence of hard non-colllnear

gluon bremsstrahlung necessitates therefore the use of observables

less sensitive to the details of hadron jet development.

All moments and especially H show strong kinematic correlations

with thrust (see Section 4.3a) which also shows the above mentionedI<P^> dependence. The use of these variables thus does not provide a

distinct advantage over the conventional analysis based on thrust.

-81 -

0 0 . 2 C M 0 . 6 0 . 8 1 .0 H 2

FIGURE 35.

The distribution of the combined high energy data ( / s ) 27 GeV) in the Fox-Wotfram moment, H 2 compared to the prediction of QCD at as = 0.23 and the quark model with< Pt > ■ 226 MeV.

-82-

FIGURE 36.

Tho Fox-Wolfram momont (distribution.

-83-

FIG U RE 37.

Tho Fox-Wol.r"am moniont distribution.

- 8 4 -

c) A Study of Inclusive Muons in Hadronic Events

In the framework of the six quark model for the weak decays of

heavy quarks, (c, b and t)copious muon production is expected from the

cascade decays t -► b ■> c [14,15]. The onset of production of a new

heavy lepton would also lead to an increase in muon production. Thus,

in addition to indications based on thrust and R measurements, a measure­

ment of inclusive muon production in hadronic final states should provide

a clear indication of the formation of top quarks or new leptons. All

the hadron data for /s from 12 to 31.6 GeV has therefore been analyzed

and scanned in a search for muons. The sample of events used in the

inclusive muon survey is a subsample of that used to measure R.

The main sources of muons in the hadron sample are decay products

of bottom and charm quarks. Background contributions to the muon signal,

arising from hadron punch through and decays in flight of plons and kaons

have been calculated using the Monte Carlo simulation (Section 3.3c) to

be ^2% at these energies. The contribution of t t events to the

H -f- hadron sample becomes negligible when the total energy cut and the

energy balance cut are applied.

Table l.V. summarizes the results for the relative production rate

of hadronic events containing muons. The table demonstrates once again

the absence of new heavy mesons up to 31.6 GeV. For /s > 30 GeVv-

the observed rate of 3.75 1 0.57% agrees with the Monte Carlo predictions

for five quark flavors, but is approximately 5 standard deviations away

from the prediction which includes the top quark.

TABLE IV

Monte Carlo predictions and data for hadronic events which include muons.

-85*

Ecm

L u m l n o a l t y

n b -' 1

Number o f H a d r o n E v e n t s

N um ber o f Muon

EV01U8

Z o f Muon

K v e u t s

M o n te C a r l o ( n o t o p )

%

M o n te C a r l o ( w i t h t o p )

%

12 9 7 . 7 239 2 0 . 8 f. 0 . 6 1 . 1 ■ 0 . 3

13 53 95 1 1 . 0 5 t. 1 . 0 1 . 2 5 0 . 3

17 60 67 2 3 , 0 • 1 . 7 *0 o o

2 7 . 4 414 188 11 5 , 8 5 1 . 8 3 . 3 > 0 . 4

30to 2804 1147 43 3 . 7 5 ' 0 , 5 7 4 . 5 ' 0 . 5 7 . 8 • 0 . 5

Figure 38 shows the thrust distribution of the hadronic events

containing muons compared to a QCD calculation containing five quark

flavors. There is very good agreement between the data and the Monte

Carlo prediction. The scarcity of events at low thrust in the figure also

rules out the existence of the top quark.

d . Discovery of Three Jet: Events

In this Gection we review the detailed topological analysis which

was used by the MARK J to unambiguously Isolate the 3-jet events arising

from the emission of hard non-collinear gluons [40] Examination of

the azimuthal distribution of energy around the thrust axis was used

to obtain a sample of planar events. An analysis of the spatial distrib­

ution of the energy flow for the planar event sample established the

underlying 3-jet structure in agren^nt with the QCD predictions for

+ “ " e e -> qqg.

-86-

■** * " * w f ■w ^»| no ■ iw »«h4hh«w ^ m»i | mm> i m > i . 11* i->-irn-m„ n r w m r n . u i w i i u m j j j x j .

• 5 . 6 . 7 . 8 . 9 1 . 0 T H R U S T

FIGURE 38.

The thrust distribution of high energy hadron events ( / s ) 27 GeV) containing at least one muon. The data (solid points) are compared to the prediction of QCD with five quark flavors.

In the reaction e + e •+ hadrons, the final states have many

appearances: spherical, 2-jet like, 3-jet like, 4-jet like, etc. Events

which fall into each of these visual categories can be produced by a

variety of underlying processes:

e + e ■+ a phase space like distribution of hadrons

e+ + e •+ q + q (quark <pt> " 200 ” 500 MeV)

-f* ~ — e + e ->q + q + gluon

and e + e •+ q + q + 2 gluons

These alternatives make any conclusions which may be drawn from the

jet-like appearance of individual ovents of little value in distinguishing

between the models, nor can such au appearance provide information about

the nature of the basic final-state constituents. Neutral particles carry a

large fraction of the total energy. When the statistics are limited it is

important to measure both charged and neutral particles. For a consistent

analysis, one must collect a statistically significant number of events

in a given kinematic region and compare the number of events in the region

with specific model predictions on a statistical basis. A meaningful

comparison with models must take into account the uncertainties in the models

such as the quark Pt distributions, fragmentation functions, etc. Before

conclusions can be drawn, background contributions from other processes

imut be understood and be kept small [41],

In order to exclude events where leading particles have escaped down

the beam pipe, or where part of a broad jet is missed, we select only

those events for which Evis > 0 ,7 /s. This cut also eliminates two~photon

events and events where a hard photon is emitted In the initial state.

The drift tubes enable us to separate more distinctly the distribution of

charged particles from neutrals. Since neutral particles carry away a

.large portion of the total energy, they will not only affect the axes of

the jets, but will also affect the identification of individual jets.

-87-

4- ~

-88-

The jet analysis of hadronic events and the search for 3-je.t events

is based on a determination of the three dimensional spatial distribution

of energy deposited in the detector. This method is quite different from

the pioneering method used by the PLUTO and TASSO groups [42], The character­

istic features of hard non-collinear gluon emission in e+e'" qqg are illustrated in

Figure 39. Because of momentum conservation the momenta of the three

particles have to be coplanar. For events where the gluon is sufficiently

energetic, and at large angles with respect to both the quark and anti­

quark, the observed hadron jets also tend to be in a recognizable plane.

This is shown in the upper part of the figure where a view down onto

the event plane shows three distinct jets; distinct because the fragment­

ation products of the quarks and gluons have limited P with respectt

to the original directions of the partons. The lower part of the figure

shows a view looking towurds the edge of the event plane, which results

in an apparent 2--jet structure. Figure 39 thus demonstrates that hard

non~co.llinear gluon emission Is characterized by planar events which

z" * q ♦ q' ♦ g — HADRONSPLANAR

FIGURE 39.

A schematic view o f the process o V ' qqg, and the throe resulting hadron jots showing the axesused to describe the event.

• 89 *

The spatial energy distribution is described in terms of three

orthogonal axes called the thrust, major and minor axes. The axes and

the projected energy flow along each axis Ttjiruat> Fraajor an<* *minor are

determined as follows:

(1) The thrust axis, e^, is defined as the direction along which the

projected energy flow is maximized. The thrust, Tt]irugt and are given by

may be used to reveal a 3-jet structure once the event plane is determined.

£ i ■ * i |l a m a x ----- -------------- ---- Lt h r u a t _ U t i

-*■1where E is the energy flow detected by a counter as described above

and Is the total visible energy of the event (E^ig).

(2) To investigate the energy distribution in the plane perpendicular

to the thrust axis, a second direction, is defined perpendicular to

e^. It is the direction along which the projected energy flow in that

plane is maximized. The quantity F,najor an^ ^ are S^ven ky

I . IE1 • e9ja i I 2 j | •+major ” max ~‘~Evi8 ’ e2 J- el

(3) The third axis., e^ is orthogonal to both the thrust and the

major axes. It is found that the absolute sum of the projected energy

flow along this direction, called , I0 very close to the minimum

of the projected energy flow along any axis, i.e.,

A i *►I, E • e J „ *<.F , » „JLL-JLL ~ minminor w , e

N i s vis

->■1 ~> E • e

If hadrons were produced according to phase-space or a qq two-jet

distribution, then the energy distribution in the plane as defined by the

major and minor axes would be isotropic, and the difference between Fraajor

anc fminor wou^c* ke small. Alternatively, if hadrons were produced via

three-body intermediate states such as qqg, and if each of the three bodies

fragments into a jet of particles with <'-, > ^ 325 MeV, the energy distrib-

ution of these events would be oblate (P refers to the final state hadrons).

Following the suggestion of H. Georgi, the quantity oblateness, 0, is defined

as

® 13 ^major “ minor

The oblateness is ^ 2 p”uon / /s for three-jet final states and is

approximately zero for final states coming from a two-jet distribution.

Figure 40a shows the event distribution as a function of oblateness

for the data at Js =■ 17 GeV where the gluon emission effect is expected to

be small. The data indeed agree with both models, although the prediction

with glucns is still preferred.

Figure 4 0 b shows the event distribution as a function of oblateness for

part of the data at 27.4 < /a < 31.6 GeV as compared with the predictions of

- - h qqg and qq models. Again, in the qq model we use both <I't> “ 325 MeV

hand ,= 425 MeV. The data have more oblate events than the qq model

predicts, but they agree with the qqg model very well. Figure 40b also

illustrates a useful feature of the oblateness: it is quite insensitive

to the details of the fragmentation process.

To study the detailed structure of the events we also divided each

event into two hemispheres using the plane defined by the major and minor

axes, and separately analyzed the energy distribution in each hemisphere

aa if it were a single jet. The jet having the smaller P with respect to

the thrust axis is defined as the "narrow" jet (n) and the other as a

17 GeV

\ QQG

QO

0 . 2

( a )

03 0.4

0 0( b )

FIGURE 40.

Differential obiateness distribution at a) / s = 17 GeV and b) at high energies (combined data) compared to the predictions of QCD {solid fine) and quark mode! (dashed lines).

9 0 ° M ajor

FIGURE 41.

Energy flow diagrams for two high energy hadronic events viewed in the major-thrust plane.

-92-

-93-

- 2 < C j o r ' FS i n o r > ■ ° b ‘ ^ m a j o r " Fm l n o r > - t h r u 8 t 0 T n a n d

VOne approach to analyzing the flat events for a possible 3-jet

structure is illustrated by Figure Al. The figure shows the energy flow

diagram for each of two high energy hadroniu events, viewed in the event

plane determined by the major and thrust axes. The energy flow diagram

is a polar coordinate plot in which *;e summed the energy vectors E*

in 10° intervals, Each point in the plot represents the summed energy

in an angular interval, with the radius given by the magnitude, and the

azimuth given by the center of the angular interval in the event plane.

The two events in the figure both show an apparent 3-jet structure.

As mentioned earlier, however, the examination of individual event

appearances cannot be used to establish the underlying 3~jet structure

characteristic of qqg final states. This is demonstrated by Figure 42,

which shows two low thrust, planar events at 12 GeV center of mass energy.

The events also show a distinct multi-jet structure. It should be noted

that all the measured distributions at low energies (thrust,oblateness,

etc.) are well described by a simple qq model, so that the suggestive event

appearances are unrelated to gluon emission, but are dominated by fluctua­

tions in the quark fragmentation process. The views of the events in the

minor-thrust plane (looking at the edge of the event plane) also show

that the events are planar.

"broad" jet (b). In each hemisphere we calculate the oblateness,

FIGURE 42.

Energy flow diagram. Two events measured at • / s = 12 GeV with the lines showing the direction and magnitude of energy deposited in the calorimeter displayed in two projections. The events appear to have a multi-jet structure in the thrust-major plane. The view in the thrust-minor plane shows the events are flat.

-94-

At the 1979 International Symposium on Lepton and Photon Interactions

at Fermilab, all DESY groups (JADE, MARK J, PLUTO and TASSO) reported evidence

for hard gluon emission. Following the conference each group published their

findings [43]. The first statistically relevant results, establishing the

3-jet pattern from q?g of a sample of hadronic events were presented t>y the

MARK J collaboration. These are shown in Figure 43 in which a sample of the

events with low thrust and high oblateness, where the gluon emission effect

is expected to be relatively large, is selected for detailed examination. The

key feature of this figure is that it consists of the superposition of an entire

event sample, and thus displays the average behavior of the energy flow for planar

events at high energy. The event sample is composed of 40 events with T < 0.8

and 0^ > 0.1 out of 446 liadronic events obtained up to the time of the Fermilab

Conference in the energy range of 27-31.6 CeV.

In the energy flow plot, all events are rotated to lie in a plane; they

are then oriented so that the longest jet is at 0° and the second longest is in the

lower half plane. Therefore, all events contributing to the substantial third

jet do have longer jets in the two other regions. In addition, it is clear that

none of the events has substantial energy flow in the regions between the jets

because the dips in these bins go nearly to zero because the energy is always

positive. All of the events thus do have a three-jet structure. Furthermore,

each event has been examined by physicists and found to be three jet like in

appearance like those shown in Fig, 41.

The calculated Monte Carlo model predictions based on QCD an both the rate

and shape of three jet events in the figure are compatible with the data with

X^ - 67 for 70 degrees of freedom. The accumulated energy distribution in the lower

part of the figure, showing the view in the plane defined by the thrust and minor

axes, exhibits a flat distribution consistent with the model predictions.

-95 •

T hrus tO e

9 0 s M a j o r 9 0 ° M i n o r

2 7 0 '

FIGU RE 43.

a. Energy distribution in the plane defined by the thrust and major axes for all events with T < 0,8 and 0^ > 0.1 at / s = 27.4, 30 and 31.S GeV obtained up to the time of the 1979 Fermilab Conference. The radial distance of the data points is proportional to the energy deposited in a 10° bin.The superimposed dashed tine represents the distribution predicted by QCD.

b. Measured and predicted energy distribution in the plane dafined by the thrust and minor axes, which shows on!y 2-jets.

These results can be contrasted to those obtained with a simple phase

space model. When viewed in the major-thrust plane, phase-space shows

three nearly identical lobes due to the method of selection used. How­

ever, at /is « 30 GeV these lobes are different in appearance from

the jets shown in Figure 43. In general, one expects the three jets

from qqg to become slimmer and easier to distinguish from the phase-

2space distribution as the center-of-mass energy increases. Using a x

fit of the phase-space energy distribution to the data we found that

2X « 222 for 70 degrees of freedom, Therefore, phase-space is inconsistent

with the data. Furthermore, large contributioiis of phase-space distribu-

tions are ruled out by our thrust distributions as shown in Figures 32-34.

For the analyses performed in the earlier part of 1979, as shown

in Figures 40 and 43, we used a Monte Carlo model implemented by P. Hoyer

et al. [44]. In the analysis discussed below, the Monte Carlo of

Ali et al. [12] was adopted. As discussed In Section 3.3c, this model

2incorporates higher order QCD effects, the q evolution of the quark

and gluon fragmentation functions and the weak decays of heavy quarks.

The QCD predictions presented in Figures 40 and 43 are not noticeably

different for the two models.

Including the running in the latter part of 1.979, the total number of

hadronic events with _> 0.7 /s has increased to 12.20 for /s > 27 GeV [45].

Figures 44 and 45 show the event distribution as a function of 0^

and 0^, compared to the predictions of the QCD model [46] and of two

quark-parton models with quark <Pfc> « 300 MeV and 500 MeV respectively [47.],

Figure 44 shows that the narrow jet distribution agtees with the various

models indicating that it comes from a single quark jet. Figure 45,

however, shows that the quark-parton models severely underestimate the

number of events with 0^ > 0.3 while the QCD model correctly predicts

the observed distribution.

-97-

-98-

1 . 0

z2 O * o * o

0 . 1

- 0 . 1 0 0 . 1 0 . 3 0 . 5

FIGURE 44.

The narrow jot oblatenesc distribution:* ™ forN dON

all hadron ovonts with measured energy Evis )0.7 / s. The data are compared to the

predictions of the QCD modol and to two quark- antiqtiark models with < Pt > « 300 MoV and

< Pt > ■= 500 MeV respectively.

1 1

- 0 . 2 0 0 . 2 0 . 6

0i1 . 0

BFIGU RE 45.

The broad jet oblatenois distribution

under tKe sam'j condition as Figure 44.

I S!il N dO,,

The T and thrust distributions of the fiat events in the region

0^ > 0,3 are shown in Figures 46 and 47 along with the QCD and high

P qq models. The observed distribution is also compared to a "flattened"

qq model in which the quarks have <Pt> " 500 MeV in the thrust-major

plane and <Pt> = 300 MeV in the thrust-minor plane. The distribution

in Figure 46 is in good agreement with the QCD model predictions and has

the same general shape as the thrust distribution for high energy

•f •“ —e e -* qq reactions shown in Figures 32 and 33. As expected the T^

distribution), however, is much broader than that of T^ and agrees only

with the QCD predictions.

The distributions in Figures 46 and 4? demonstrate that the relative

yield of flat events, and the shape of these events as measured by T^

and T^, can only be explained by the QCD model. The distributions T^ and

T^ further exclude phase space (which peaks at lower thrust values) as well

as qq models as possible explanations of the energy flow plots.

The development of the 3-jet structure with decreasing thrust and

increasing oblatcness, as predicted by QCD [48], is shown in a series

of energy flow diagrams in Figures 48-50.

As seen in Figure 48 the events at high thrust values are dominated

+ -by a 2-jet structure characteristic of e + e -► q + q. In Figure 49,

where the thrust is lower, we begin to see the appearance of the gluon

jet; and in Figure 50 the 3-jet events are predominant. It is important

to note that in all three cases the data agree with the QCD model prediction,

• 101 -

Z

X )

. Z I — . * U 4

T

ALL DATA

Q C D

qCj(500)

q q (500,300)

0 . 6

T n

0 . 8 1.0

FIGURE 46.Tho thrust distribution of the narrow jet for events with O k > 0.3. Also shown are the various model predictions including a flattened qq (600, 300) discussed In the text. Note the narrow jet thrust distribution is consistent with thrust distribution of all tho hadron events labelled "A L L DATA". This curve is normalized to the data of Figure 33.

- 102-

z* 0

0 0

" O

•|z

T b

FIGURE 47.The thrust distribution of the broad jets for events with 0[j ) 0.3. The curves are discussed in the text.

\

90° Major v » 1 1 / .

\

\ //

/ \

/ \

-4 2 %

/ \

1 1 1 1 '

270°

FIGURE 48.

Energy flow diagram in the thrust-major plane for high energy data (27-31.6 GeV) with T ) 0.9.The solid line is the prediction of QCD.

9 0 ° M a j o r

\ > i ' / .

\ /

\ /\ /

\ /

\

i— t /I %

\

i 1 1 '

2 7 0 °FIGURE 49.

Same as Figure 43 for events with 0.8 S T 5 0.9 and broad jet oblateness 0^ ) 0.1

90° Major . 1 . ,

\ /\

\

T h r u s t

0 - 180'

/ \

\

1 %/ \

FIGURE 50

Same 2 s Figure 48 for events with T < 0.8 arvd O b > 0.1

showing the increased incidence of hard non-colllnear gluon emission with

decreasing thrust and Increasing oblateness. The energy flow in the

minor-thrust plane contains only two nearly Identical lobes similar to

the narrow jet in Figure 43b, in good agreement with QCD predictions. In

Figure 51 we unfold the energy flow diagram of Figure 50 to see more

clearly the comparison of the data with the predictions of QCD,

qq (<Pt> “ 500 MeV), and a "mixed model" consisting of a combination of

qq and phase-space contributions. All models in Figure 51 are normalized

to have the same areas (as the data) before the individual cuts are

imposed. The normalization for the mixed model wa3 determined by

adjusting the qq (<P > *■ 300 MeV) and phase~space contributions to agree

with the measured thrust distribution as illustrated in Figure 52, As

seen in Figure 51, only QCD can describe the observed 3-jet structure,

The conclusions obtained by the JADE, PLUTO and TASSO collaborations on their

tests of Q ,C ,D . and studies of multi-jet events are in good agreement with us,

(See section 4.4).

A very powerful method to eliminate phase-space as a source of

the 3-jet events and in fact eventually to study the nature of the

individual jets is shown in Figure 53. Here the thrust distributions

U J l 'Q .■oto

— | U J

<t>

FIGU RE 51.

The unfolded energy flow diagram of Figure 50 as compared to QCD, the quark model ( ( ) = 500 MeV)and a mixed qq and phase space model (see text).

- 108 -

T h r u s t

FIGU RE 52,

Illustration of the method usod In determining the maximum permissible admixture of phase-space toqpin the mixed model shown in Figure 51.

-u - 1 d NThrust distribution — — N dT

FIGURE 53.

for each ind:vidua! jet in the 3- jet sample of Figure 50 which were selected by

using 0^ >0.1 and thrust < 0.8. The corresponding distribution normalized to the tame total number of 3-jet events are also shown for QCO (solid curve)

and phase-space model (dashed curve).

109-

of each of the jets, separated according to their position in the

energy flow figure are compared to the expectations of QCD and phase-

space. The thrust distributions agree well with the QCD prediction

but are in strong disagreement with phase space predictions.

e) Determination of the Strong Coupling Constant as

Recent experiments on scaling violations in lepton inelastic

scattering [49 ], on high P events in dilepton production by hadrons [50 ],

-fand multi-jet events in e e annihilations [37, 40, 51] all indicate that the

rer.ults are explained naturally in the quantum chromodynamics (QCD)

theory of the strong interaction of quarks and gluons [7], The strong

2coupling constant a (q ) between quarks and gluons has been measured

s

indirectly in quarkonium bound states [52.], and in deep inelastic exper-

2iments [49]. At PETRA, where thft q is much larger, computations are

~L -

expected to be more reliable. In addition, high energy e e annihilations

offer a more direct way of measuring a and testing perturbative QCDSbecause it is expected to give rise to multi-jets which can be system­

atically identified.

The 3-jet events discussed in the previous section, which consist

of qqg fragmentation products with relatively small backgrounds from

fluctuations of phase-space-like processes or quark-antiquark intermediate

states, allow us to make further comparisons of the event properties

with the predictions of QCD. In particular the relative yield of 3-jet

events and the shape distribution gives a way to measure directly a , thes

strong coupling constant,

We used several methods in determining the strong coupling

constant a , including:8

1) the average oblateness <0^,

2) the fraction of events with 0^ > 0.3,

3) the relative yield of events with 0^ - 0n > 0.3 where 0n is

constrained to be greater than zero.

-110-

For each quantity we allowed a to vary In the QCD model, and we3

then determined the range of a values for which the QCD model predictionss

agree with the data within errors. In particular, the samples obtained

using criteria 2) and 3) consist predominantly of 3-jet events from

»}• -• •*e e ■* qqg, In which the gluon emitted is both very energetic and at a

large angle with reapect to both the quark and antiquark, This leads to

an event sample where the number of events in the sample is a quasl-linear

function of a , and in which the influence of non-perturbative effects which s

are not calculable in QCD is minimal, For criterion 2), for example,

we observed 161 events, which matches the QCD model with a =» 0,23.s

■j* •»The e e -* qq contribution is calculated to be 21 events. The predominance

of qqg in a sample with > 0.3 is maintained even if <Pt> is allowed to

vary from 225 MeV to 500 MeV in the model. With <Pt> " 300 MeV the

e e -»■ qq contribution is calculated to be 58 events.

The methods described above yield a self-consistent set of a values,s

as illustrated in Figure 54. On the basis of the results of the three

methods we obtain

*» 0.23 ± 0.02 (statistical error)

± 0.04 (systematic error)

The large systematic error was mostly due to uncertainties in

QCD calculations [12]. For method 2) the ranse of a due to variations

in <P > from 225 to 400 MeV is ± 0.01 and the change in a due to dif- c s

ferent cuts in 0, from 0, > 0.3 to 0. > 0.15 or cuts in 0 from no cuts b b b n

to |O | is -0.01. For method 2), changing the fragmentation

function z.D(z) to l~z for u, d and s quarks and zD(z) to z for c and

C Ob

< * s

FIGURE 64.

The left graph: The average value of oblatertoss < Ob > for all events with 6 yjs ;> 0-7 J s as a function of

fts, computed by varying a & In the QCD model.

Therightgraph: The fraction of hadronic events with 0^ > 0.3 ( orgj) as a function of a s InthoQCD model.

-113-

b q u a r k s d o e s n o t c h a n g e t h e a v a l u e n o t i c e a b l y . T a b l e s V a n d V ISs h o w i n d e t a i l t h e c h a n g e o f a g w i t h r e s p e c t t o t h e 0 ^ c u t s a n d 0 ^ c u t s .

O u r v a l u e o f a i s c o n s i s t e n t w i t h t h e v a l u e o f t h e J A D E g r o u p 8

o b t a i n e d w i t h a d i f f e r e n t M o n t e C a r l o p r o g r a m . ( S e e s e c t i o n 4 . 4 ) , T h e

v a l u e o f a [ 4 5 , 5 3 ] i s i n q u a l i t a t i v e a g r e e m e n t , w i t h t h e v a l u e s o b t a i n e d s

i n d e e p i n e l a s t i c l e p t o n n u c l e o n s c a t t e r i n g e x p e r i m e n t s [ 4 9 ] , a n d i n t h e

a n a l y s i s o f t h e q u a r k o n i u m s t a t e s [ 5 2 ] , H o w e v e r , d e t a i l e d c o m p a r i s o n

a m o n g t h e s e r e s u l t s c a n n o t y e t b e m a d e w i t h o u t a c c u r a t e h i g h e r o r d e r Q C D

c a l c u l a t i o n s .

TABLE V

Value of as with different 0^ cuts, without cuts in On and Pt = 247 MeV.

0 . 1 5 0 . 2 2 ± 0 . 0 2

0 . 2 0 0 . 2 2 + 0 . 0 2

0 . 2 5 0 . 2 2 x 0 . 0 2

0 . 3 0 0 . 2 3 ± 0 . 0 2

TABLE V I

Value of «s with different I0n t cu+s, with 0 b > 0.3 and < Pt> = 2/)7 MeV.

N o C u t s 0 . 2 3 + 0 . 0 2

0 . 2 4 0 . 2 3 + 0 . 0 2

0 . 2 0 0 . 2 3 ± 0 . 0 2

0 . 1 6 0 . 2 3 + 0 . 0 2

0 . 1 2 0 . 2 2 ± 0 . 0 3

0 . 0 8

< - ........- ......... ........ - ..... .............

0 . 2 2 + 0 . 0 3

4 . 4 C o m p a r i s o n w i t h o t h e r e x p e r i m e n t s a t P E T R A

O u r d e t e c t o r u s e s c a l o r i m e t r i c t e c h n i q u e s w h i c h a r e v e r y d i f f e r e n t

f r o m o t h e r P E T R A g r o u p s ( J A D E , P L U T O a n d T A S S O ) w h i c h u s e s o l i n o i d a l m a g n e t i c

f i e l d f o l l o w e d b y p a r t i c l e i d e n t i f i c a t i o n d e v i c e s . T h e s e d i f f e r e n c e s i n

t e c h n i q u e i m p l y t h a t t h e e v e n t s e l e c t i o n c r i t e r i a , M o n t e C a r l o a n a l y s i s

p r o g r a m s , a n d t h e a s s i g n m e n t o f s y s t e m a t i c e r r o r s a r e q u i t e d i f f e r e n t . H o w e v e r ,

d e s p i t e t h e d i f f e r e n t t e c h n i q u e s u s e d t h e r e s u l t s o f a l l t h e P E T R A g r o u p s a r e

c o m p l e m e n t a r y a n d s u p p o r t i v e o f e a c h o t h e r i n t h e i r p h y s i c s c o n c l u s i o n s o n t h e

t e s t o f Q E D [ 5 4 ] , o n t h e m e a s u r e m e n t o f R , t h e s e a r c h f o r n e w f l a v o r s [ 5 1 , 5 5 ]

a n d o n t h e e f f e c t s o f h a r d g l u o n j e t s [ 5 1 , 5 6 ] .

-115-

I n t h e f i r s t y e a r o f e x p e r i m e n t a t i o n w i t h a s i m p l e d e t e c t o r ,

w e h a v e o b t a i n e d t h e f o l l o w i n g r e s u l t s

1 ) We h a v e e s t a b l i s h e d t h e v a l i d i t y o f q u a n t u m e l e c t r o d y n a m i c s t o a

“ 1 6d i s t a n c e < 2 x 1 0 c m . E l e c t r o n s , m u o n s a n d t a u l e p t o n s a r e

—1 6p o i n t - l i k e w i t h s i z e s s m a l l e r t h a n 2 x 1 0 c m .

2 ) T h e r e l a t i v e c r o s s s e c t i o n s a n d e v e n t d i s t r i b u t i o n s s h o w t h a t t h e r e

i s n o n e w c h a r g e 2 / 3 q u a r k p a i r p r o d u c t i o n u p t o / e - 3 1 . 6 G e V .

3 ) T h e e n e r g y f l o w o f e v e n t s a t h i g h e n e r g i e s i s i n g o o d a g r e e ­

m e n t w i t h q u a n t u m c h r o m o d y n a m i c s . T h e q u a n t i t y o f f l a t e v e n t s

a n d t h e i r d i s t r i b u t i o n s d i s a g r e e w i t h t h e s i m p l e q u a r k

a n t i q u a r k m o d e l p r e d i c t i o n .

4 ) We h a v e d i s c o v e r e d 3 - j e t e v e n t s ; t h e r a t e o f t h e i r p r o d u c t i o n a n d

t h e i r d i s t r i b u t i o n a g r e e w i t h t h e p r e d i c t i o n o f Q C D ,

5 ) We h a v e m e a s u r e d t h e s t r o n g i n t e r a c t i o n c o u p l i n g c o n s t a n t a .s

T h e r e a r e t w o r e a s o n s w h i c h m a d e i t p o s s i b l e t o o b t a i n t h e s e r e s u l t s :

1 ) I n e e c o l l i s i o n s , t h e s i g n a l i s c l e a r a n d u n i q u e . E v e r y

e v e n t h a s a d e f i n i t e p h y s i c a l i n t e r p r e t a t i o n a n d c a n b e a n a l y z e d

i n t e r m s o f Q E D o r Q C D . T h i s i s q u i t e d i f f e r e n t f r o m o u r p r e v i o u s e x p e r i e n c e

w i t h p r o t o n p r o t o n c o l l i s i o n s w h e r e t h e s i g n a l o f t h e v i r t u a l p h o t o n

5) Conclusions

events is less than one part in 10 of the background.

*116-

2 ) P E T R A w a s r e l i a b l y c o n s t r u c t e d a n d a v a i l a b l e f o r u s e b y

e x p e r i m e n t a l i s t s f r o m t h e b e g i n n i n g .

A C K N O W L E D G E M E N T S

We w i s h t o t h a n k P r o f e s s o r s H . S c h o p p e r , G . V o s s , A . N . D i d d e n s ,

I I . P ' n l H H n c r , K . l . o h r m a n n , F . L o w , D r s . F . J . E p p l i n g a n d 0 . S o e h n g e n f o r

t h e i r v a l u a b l e s u p p o r t a n d A . A l i , A . D e R u j u l a , H . G e o r g i , S . G l a s h o w ,

.1. K o u p i h U H s , T . D . L e e , F,. P i e t a r i n e n , T . W a l s h , L . L . W a n g f o r h e l p f u l

d J h c u b h t o n s .

REFERENCES

[ 1 ] P E T R A P r o p o s a l ( u p d a t e d v e r s i o n ) , D E S Y , H a m b u r g , ( F e b r u a r y , 1 9 7 6 ) .

[ 2 ] G . V o s s , T h e 1 9 G e V e + e S t o r a g e R i n g , I n t e r n a l R e p o r t , D E S Y M / 7 9 / 1 6 .

( 3 } S . W . H e r b e t a l . , P h y s . R e v . L e t t . 3 9 > 2 5 2 ( 1 9 7 7 ) .

[ 4 ] C . W . D a r d e n e t a l . , P h y s . L e t t . 7 6 B , 2 4 6 ( 1 9 7 8 )

C h . B e r g e r e t a l . , P h y s . L e t t . 7 6 B , 2 4 3 ( 1 9 7 8 )

J . K . B i e n l e i n e t a l . , P h y s . L e t t . 7 8 B t 3 6 0 ( 1 9 7 8 ) .

C . W . D a r d e n e t a l . , P h y s . L e t t . 7 8 B , 3 6 4 ( 1 9 7 8 ) .

[ 5 ] A . F e b e l a n d G . H e r a m i e , " P I A , t h e P o s i t r o n I n t e n s i t y A c c u m u l a t o r f o r

t h e P E T R A I n j e c t i o n , " I n t e r n a l R e p o r t , DESY M / 7 9 / 1 3 .

+ -[ 6 ] U . B e c k e r e t a l . , " A S i m p l e D e t e c t o r t o M e a s u r e e e R e a c t i o n s a t H i g h

E n e r g y , " P r o p o s a l t o P E T R A R e s e a r c h C o m m i t t e e , ( M a r c h 1 9 7 6 ) .

[ 7 ] D . J . G r o s s a n d F . A . W i l c z e k , P h y s . R e v . L e t t . 30.* 1 3 4 3 ( 1 9 7 3 ) .

H . D . P o l i t z e r , P h y s . R e v . L e t t . 3 0 , 1 3 4 6 ( 1 9 7 3 )

J . E l l i s e t a l . , N u c l . P h y s . B 1 U , 2 5 3 ( 1 9 7 6 )

T . d e G r a n d e t a l . , P h y s . L e t t D 1 6 , 3 2 5 1 ( 1 9 7 7 )

G . K r a m e r e t a l . , P h y s . L e t t . 7 9 B , 2 ^ 9 ( 1 9 7 8 )

A . D e R u j u l a e t a l . , N u c l . P h y s . B 1 3 8 , 3 8 7 ( 1 9 7 8 )

P . H o y e r e t a l . , D E S Y P r e p r i n t 7 9 / 2 1 ( u n p u b l i s h e d ) .

A . A l i e t a l . , P h y s . L e t t . 8 2 B , 2 8 5 ( 1 9 7 9 ) ; a l s o D E S Y R e p o r t 7 9 / 5 4 s u b m i t t e d

t o N u c l . P h y s . B .

[ 8 ] P . D . I . u c k e y e t a l . , P r o c e e d i n g s o f t h e I n t e r n a t i o n a l S y m p o s i u m o n E l e c t r o n

a n d P h o t o n I n t e r a c t i o n s a t H i g h E n e r g i e s , H a m b u r g , 1 9 6 5 ( S p r i n g e r , B e r l i n 1 9 6 5 ) ,V o l . I I . , p 3 9 7 .

[ 9 ] J . F . C r a w f o r d e t a l . , N u c l . I n s t r u m . M e t h o d s 1 2 7 , 1 7 3 ( 1 9 7 5 ) .

[ 1 0 ] U . B e c k e r e t a l . , N u c l . I n s t r u m . M e t h o d s 1 2 8 , 5 9 3 ( 1 9 7 5 ) .

[ 1 1 ] H . N e w m a n , P r o c e e d i n g s o f t h e 1 9 t h I n t e r n a t i o n a l C o n f e r e n c e o n H i g h E n e r g y

P h y s i c s , T o k y o , J a p a n , ( A u g u s t 1 9 7 8 ) , I n t e r n a t i o n a l A c a d e m i c P r i n t i n g C o .

L t d . , J a p a n .

REFERENCES (continued)

( 1 2 ] A . A l l , E . P i e t a r i n e n , G . K r a m e r a n d J , W i l l r o d t , D E S Y R e p o r t 7 9 / 8 6 ,

( 1 9 7 9 ) . I n t h e i r p r o g r a m t h e c o n t r i b u t i o n d u e t o 4 - j e t p r o d u c t i o n l a

i n c l u d e d . T h e v i r t u a l g l u o n c o r r e c t i o n d u e t o 3 - j e t r a t e , h o w e v e r , i s

n o t i n c l u d e d .

( 1 3 ] R . D , F i e l d a n d R . P . F e y n m a n , N u c l . P h y s . B 1 3 6 , 1 ( 1 9 7 8 ) .

( 1 4 ] M . K o b a y a s h i a n d T . M a s k a w a ( P r o g r . T h e o r . P h y s . 4 9 , 6 5 2 ( 1 9 7 3 ) .

+ -( 1 5 ] A . A l i e t a l . , H e a v y Q u a r k s i n e e A n n i h i l a t i o n , D E S Y R e p o r t 7 9 / 6 3 ,

( 1 9 7 9 ) .

[ 1 6 ] F . A . B e r e n d s e t a l . , F h y s . L e t t 6 3 B , 4 3 2 ( 1 9 7 6 ) .

G . B o n n e a u a n d F . M a r t i n , N u c l . P h y s . B 2 7 , 3 8 1 ( 1 9 7 1 ) .

Y . S . T a a i , R e v . M o d . P h y s . 4 6 , 8 1 5 ( 1 9 7 4 ) .

L . W . Mo a n d Y . S . T s a i , R e v . M o d . P h y s . 4 1 , 2 0 5 ( 1 9 6 9 ) .

[ 1 7 ] J . A . M . V e r m a s e r e n , C E R N , ( t o b e p u b l i s h e d ) . We w i s h t o t h a n k D r . V e r t n a s e r e n

f o r h e l p f u l a s s i s t a n c e .

( 1 8 ] H . G . S a n d e r s , D i p l o m a r b e i t , P h y s i k a l i s c h e s I n s t i t u t , A a c h e n , R e p o r t N o . H E P

7 4 / 0 7 , ( 1 9 7 4 ) ( u n p u b l i s h e d ) .

[ 1 9 ] T . A . G a b r i e l a n d R . L . B i s h o p , N u c l . I n a t r . M e t h o d s 1 5 5 * 8 1 ( 1 9 7 8 ) a n d r e f e r e n c e s

t h e r e i n .

( 2 0 ] F . A . B e r e n d s e t a l . , N u c l . P h y s . B 6 8 , 5 4 1 ( 1 9 7 4 ) .

( 2 1 ] R . L . F o r d a n d W . R . N e l s o n , 3 L A C R e p o r t - 2 1 0 , u n p u b l i s h e d .

[ 2 2 ] G , R i p k e n , P r i v a t e c o m m u n i c a t i o n . We w o u l d l i k e t o t h a n k D r . R i p k e n f o r h i s

v a l u a b l e a s s i s t a n c e .

[ 2 3 ] V . A l l e s - B o r e l l i e t a l . , N u o v o C i m e n t o 7 A , 3 4 5 ( 1 9 7 2 ) .

H . N e w m a n e t a l . , P h y s . R e v . L e t t . . 3 2 , 4 8 3 ( 1 9 7 4 ) .

J - E . A u g u s t i n e t a l . , P h y s . R e v . L e t t . 3>i» 2 3 3 ( 1 9 7 5 ) .

L . H . O ’ N e i l l e t a l . , P h y s . R e v . L e t t . 3 7 , 3 9 5 ( 1 9 7 6 )

[ 2 4 ] D . P . B a r b e r e t a l . , P h y s . R e v . L e t t . 4 £ , m o ( 1 9 7 9 )

[ 2 5 ] S . J . B r o d s k y a n d S . D . D r e l l , A n n u . R e v . N u c l . S c i . 2 0 , 1 4 7 ( 1 9 7 0 ) .

{ 2 6 ] A D O N E P r o p o s a l I N F N / A E - 6 7 / 3 , ( M a r c h 1 9 6 7 ) , A D O N E - F r a s c a t i ( u n p u b l i s h e d )

a n d M . B e r n a r d i n i e t a l . , ( Z i c h i c h i G r o u p ) , N u o v o C i m e n t o 1 7 A , 3 8 3 ( 1 9 7 3 ) .

S . O r i t o e t a l . , P h y s . L e t t . 4 8 B , 1 6 5 ( 1 9 7 4 ) .

REFERENCES (continued)

[ 2 7 ] M . P e r l f i t a l . , P h y s . R e v . L e t t . 1 5 , 1 4 8 9 ( 1 9 7 5 ) .

G . F e l d m a n e t a l . , P h y s . R e v . L e t t 3 8 , 1 1 7 ( 1 9 7 7 ) .

[ 2 8 ] J . B u r m e s t e r e t a l . , P h y s . L e t t . 6 8 B , 2 9 7 ( 1 9 7 7 ) .

J . B u r m e s t e r e t a l . , P h y s . L e t t . 6 8 B , 3 0 1 ( 1 9 7 7 ) .

[ 2 9 ] F o r a r e v i e w o f o u r p r e s e n t k n o w l e d g e o f t h e T l e p t o n , s e e G u e n t e r F l u e g g e ,

Z e i t s c h r . f . P h y s i k C l , P a r t i c l e s a n d F i e l d s , 1 2 1 ( 1 9 7 9 ) , a n d t h e r e f e r e n c e s

t h e r e i n .

[ 3 0 ] R . H o f a t a d t e r , P r o c e e d i n g s o f t h e 1 9 7 5 I n t e r n a t i o n a l S y m p o s i u m o n

L e p t o n a n d P h o t o n I n t e r a c t i o n s a t H i g h E n e r g i e s ( S t a n f o r d L i n e a r

A c c e l e r a t o r C e n t e r , S t a n f o r d , C a l i f o r n i a , 1 9 7 5 ) 8 6 9 .

[ 3 1 ] S.I>. D r e l l , A n n , P h y s . ( N . Y . ) 4 , 7 5 ( 1 9 5 8 ) .

T . D . L e e a n d G . C . W i c k , P h y s . R e v . D 2 , 1 0 3 3 ( 1 9 7 0 )

[ 3 2 ] D . P . B a r b e r e t a l . , P h y s . R e v . L e t t . 4 3 , 1 9 1 5 ( 1 9 7 9 ) .

[ 3 3 ] H . T e r a z a w a , R e v , M o d . P h y s . 4 J > , 6 1 5 ( 1 9 7 3 ) . We u s e d o ( y y > mu I t i p i o n )

» ■2 4 0 - 2 7 0 / W 2 | n b . W i s t h e e n e r g y o f t h e t w o - p h o t o n s y s t e m .

[ 3 4 ] Y . S . T s a i , P h y s . R e v . DA, 2 8 2 1 ( 1 9 7 1 ) .

H . B . T r a c k e r a n d J . J . S a k u r a i , P h y s . L e t t . 3 6 B , 1 0 3 ( 1 9 7 1 ) .

K . F u j i k a w a a n d N . K a w a m o t o , P h y s . R e v . D 1 4 , 5 9 ( 1 9 7 6 ) .

S e e a l B o R e f e r e n c e 2 8 .

[ 3 5 ] J . L . R o s n e r , C . Q u i g g , H . B . T h a c k e r , P h y s . L e t t . 7 4 B , 3 5 0 ( J 9 7 8 ) .

C , Q u i g g , c o n t r i b u t i o n t o t h e 1 9 7 9 I n t e r n a t i o n a l S y m p o s i u m o n L e p t o n

a n d P h o t o n I n t e r a c t i o n s , F e r m i l a b .

M. G r e c o , P h y s . L e t t . 7 7 B , 8 4 ( 1 9 7 8 ) .

[ 3 6 ] T . A p p l e q u i s t a n d H . G e o r g i , P h y s . R e v . D 8 , 4 0 0 0 ( 1 9 7 3 ) .

A . Z e e , P h y s . R e v . D 8 , 4 0 3 8 ( 1 9 7 3 ) .

( 3 7 } D . P , B a r b e r e t a l . , P h y s . R e v . L e t t . 4 2 , 1 1 1 3 ( 1 9 7 9 ) ,

D . P . B a r b e r e t a i . , P h y s . R e v . L e t t * 4 3 , 9 0 1 ( 1 9 7 9 ) ,

D . P . B a r b e r e t a l . , P h y s , L e t t . 8 5 B , 4 6 3 ( 1 9 7 9 ) .

F o r a t h e o r e t i c a l d i s c u s s i o n o n t h o u s e o f t h r u s t v a r i a b l e s s e e :

E . F a r h i , P h y s . R e v . L e t t . 3 9 , 1 5 8 7 ( 1 9 7 7 ) .

S . . B r a n d t e t a l . , P h y s . L e t t 1 2 , 5 7 ( 1 9 6 4 ) .

REFERENCES (continued)

S . B r a n d t a n d H . D a h m e n , Z e i t a c h r . f . P h y s . C l , 6 1 ( 1 9 7 9 ) .

[ 3 8 ] R . S c h w i t t e r s , P r o c e e d i n g s o f t h e 1 9 7 5 I n t e r n a t i o n a l S y m p o s i u m o n

L e p t o n a n d P h o t o n I n t e r a c t i o n s a t H i g h E n e r g i e s ( S t a n f o r d L i n e a r

A c c e l e r a t o r C e n t e r , S t a n f o r d , C a l i f o r n i a , 1 9 7 5 ) 5 .

G . H a n s o n e t a l . , P h y s . R e v . L e t t . 35. , 1 6 0 9 ( J 9 7 5 ) .

G . H a n s o n , T a l k a t t h e 1 3 t h R e c o n t r e d e M o r i o n d , L e s A r c s , F r a n c e ,

( M a r c h 1 2 - 2 6 , 1 9 7 8 ) , S L A C - P U B 2 1 1 8 ( 1 9 7 8 ) .

[ 3 9 ] G . C . F o x a n d S . W o l f r a m , P h y s . R e v . L e t t . 4 1 , 1 5 8 1 ( 1 9 7 8 ) .

G . C . F o x a n d S . W o l f r a m , N u c l . P h y s . B 1 4 9 , 4 1 3 ( 1 9 7 9 ) .

G . C . F o x a n d S . W o l f r a m , P h y s . L e t t . 8 2 B , 1 3 4 ( 1 9 7 9 ) .

[ 4 0 ] D . P . B a r b e r e t a l . , P h y s . R e v . L e t t . 4J3, 8 3 0 ( 1 9 7 9 ) .

[ 4 1 ] O h . B e r g e r e t a l . , P h y s . L e t t . 8 6 B , 4 1 8 ( 1 9 7 9 ) , h a v e p r e s e n t e d a

s y s t e m a t i c s t u d y i n t h e s e l e c t i o n o f 3 - j e t e v e n t s f r o m q q a n d 3 - j e t

e v e n t s f r o m q q g ( s e e T a b l e s 1 a n d 2 o f t h e i r p a p e r ) .

[ 4 2 ] C h . B e r g e r e t a l . , P h y s . L e t t . 7 8 B , 1 7 6 ( 1 9 7 8 ) .

S . B r a n d t a n d H . D a h m e n , Z e i t a c h r . f . P h y s . C l , 6 1 1 9 7 9 ) .

B . H . W i i k , P r o c . I n t e r n . N e u t r i n o C o n f , ( B e r g e n , N o r w a y , J u n e 1 9 7 9 ) .

P . S o e d i n g , E u r o p e a n P h y s i c a l S o c i e t y C o n f e r e n c e R e p o r t , J u l y ( 1 9 7 9 ) .

T h i s r e p o r t i n c l u d e s f i v e e v e n t s o f . 3 - j e t s o f c h a r g e d p a r t i c l e s .

E a c h e v e n t h a s a m e a s u r e d e n e r g y ^ -x o f t h e t o t a l e n e r g y , T h e i j r p r e d i c t i o n

f o r q q g w a s 9 e v e n t s w i t h a n u n s t a t e d 3 - j e t b a c k g r o u n d f r o m q q .

S t a t i s t i c a l l y s i g n i f i c a n t r e s u l t s o n p l a n a r e v e n t s h a v e b e e n p u b l i s h e d

( s e e T a b l e 4 ) i n R . B r a n d © : i k e t a l . , D E S Y - P r e p r i n t 7 9 / 6 1 ( 1 9 7 9 ) .

[ 4 3 ] D . P . B a r b e r e t a l . , ( M A R K J C o l l a b o r a t i o n ) p h y s . R e v . L e t t . 4 3 ,

8 3 0 ( 1 9 7 9 ) . M . I . T . R e p o r t 1 0 6 , A u g u s t 2 8 , 1 9 7 9 .

R . B r a n d e l i k e t a l . , ( T A S S O C o l l a b o r a t i o n ) P h y s . L e t t . 8615, 2 4 3 ( 1 9 7 9 ) .

C h . B e r g e r e t a l . , ( P L U T O C o l l a b o r a t i o n ) P h y s , L e t t . 8 6 B , 4 1 8 ( 1 9 7 9 ) .

W . B a r t e l e t a l . , ( J A D E C o l l a b o r a t i o n ) D E S Y r e p o r t 7 9 / 7 7 ( 1 9 7 9 ) .

s e e a l s o H . S c h o p p e r , D E S Y R e p o r t 7 9 / 7 9 ( 1 9 7 9 )

[ 4 4 ] P . H o y e r e t a l . , D E S Y R e p o r t 7 9 / 2 1 ( 1 9 7 9 ) .

[ 4 5 ] D . P . B a r b e r e t a l . , P h y s , L e t t . 8 9 B , 1 3 9 ( 1 9 7 9 ) .

f 4 6 J T h e d a t a i n F i g s . 4 4 a n d 4 5 a t 0 < 0 . o r 0 < 0 I s d u e t o s t a t i s t i c a l f l u c t u a t i o n s ,

a n d t h e e n e r g y r e s o l u t i o n J E - 2 0 ' /, a n d p o s s i b l e n h i g h e r o r d e r Q C D e f f e c t s .

E

[47] In Figs. 45-51 if we choose quark <Pt> <300 MeV we observe larger deviations between q'q' model and the data.

[48] A. DeRujula et a l . 4 NucJ. Phys. B 138, 387 (1978).

[49] H.L. Anderson et al., Phys. Rev. Lett. 4 0, 1061 (1978).

P.C. Bosetti et al., Nucl. Phys. B 142, 1 (1978).

J.G.H. de Groot et al., Zeitschr. f. Phys. Cl, 143 (1979).

J.G.H. de Groot et al., Phys. Lett. 82B, 292 (1979).

J.G.H. de Groot et al., Phys. Lett. 8 2 B , 456 (1979).

[50] D. Antreasyan it al., (to be published).

[51] W. Bartel et al., (the JADE Collaboration), Phys. Lett. 8 8 B , 171 (1979).

W. Bartel et al., (the JADE Collaboration), Phys. Lett. ;89B, 136 (1979).

Ch. Berger et al., (the PLUTO Collaboration), Phys, Lett. 8IB, 410 (1979).

Ch. Berger et al., (the PLUTO Collaboration), Phys. Lett 86B, 413 (1979).

Ch. Berger et al., (the PLUTO Collaboration), Phys. Lett. 86B, 418 (1979).

Ch. Berger et al., (the PLUTO Collaboration), Phys. Lett. 89B, 120 (1979).

R. Brandelik et al., (the TASSO Collaboration), Phys. Lett. 83B, 261 (1979),

R. Brandelik et al., (the TASSO Collaboration), Phys. Lett. 86B, 243 (1979)

R. Brandelik et al., (the TASSO Collaboration), Phys. Lett. 88B, 199 (1979).

R. Brandelik et al., (the TASSO Collaboration), Phys. Lett. 89B, 418 (1980).

[52] M. Krammer and H. Krasemann, DESY Report 78/66 (1978).

2[53] It is not yet clear which q should be used to extract A to compare quantitatively

with other data.

[54] S. Oritc (JADE Collaboration), invited talk 1979 Symposium at FNAL and DESY Report 79/64, 1979.

Ch. Berger et al., (the PLUTO Collaboration), DESY Report 80/01.

[55] Ch. Berger et al., (the PLUTO Collaboration), DESY Report 80/02,

W. Bartel et a l . , (the JADE Collaboration), DESY Report 80/04.

[56] W. Bartel et al., (the JADE Collaboration). DESY Report 79/80.

Ch. Berger et a l . , (the PLUTO Collaboration), DESY Report 79/83.

REFERENCES ( c o n t i n u e d )