Particle production in pp and Pb-Pb collisions with the ALICE experiment at the LHC
F. Bellini* for the ALICE Collaboration *Università di Bologna, I.N.F.N Sez. di Bologna – Italy
Rencontres de Moriond - QCD and High Energy Interactions La Thuile, 14th March 2012
Outline
The ALICE detector at LHC
Results in pp collisions
Results in Pb-Pb collisions
Medium evolution and (selected) “soft” probes
Summary and conclusions
14/03/12 F. Bellini, Rencontres de Moriond -‐ QCD 2
Iden=fied primary par=cle spectra
Test of hydrodynamic model
Blast-‐wave fit to spectra
Mul=-‐strange baryon spectra
Par=cle ra=os tes=ng thermal model
Strange baryon/meson ra=o
Strangeness enhancement
Iden=fied primary par=cle spectra and ra=os
Resonances spectra
Mul=-‐baryon spectra
Comparison with Monte Carlo (MC) models
pp collisions PbPb collisions
ITS
TPC
TOF
The ALICE detector at LHC
14/03/12 F. Bellini, Rencontres de Moriond -‐ QCD 3
Inner Tracking System – ITS: Primary vertex, PID via dE/dx Time Projec9on Chamber – TPC: Global tracking, PID via dE/dx Time Of Flight system – TOF: PID via =me-‐of-‐flight measurement
• Unique PID capabili=es: dE/dx, =me-‐of-‐flight, Cherenkov, transi=on radia=on, calorimetry, decay topology (V0, cascades)
• Central region with the smallest material budget at the LHC
pp collisions at √s = 0.9 and 7 TeV
14/03/12 F. Bellini, Rencontres de Moriond -‐ QCD 4
Transverse momentum spectra (pT) of identified π, K and p, resonances and multi-strange
baryons, as well as particle ratios measured in pp collisions:
o Provide valuable reference spectra for the understanding of heavy ion data
o Allow to constrain the phenomenology of QCD-inspired models (Pythia, Phojet …)
Primary π/K/p spectra
14/03/12 F. Bellini, Rencontres de Moriond -‐ QCD 5
-1 |y|<
0.5
(G
eV
/c)
tdN
/dp
INE
L1/N
-310
-210
-110
= 7 TeVspp at 2+stat2syserror=
Preliminary
Normalization Error 8.3%
p
Phojet
Pythia D6T
Pythia Perugia0
Pythia Perugia 2011
(GeV/c)t
p0 0.5 1 1.5 2 2.5 3
MC
/data
0
0.5
1
1.5
2
-1 |y|
<0
.5 (
Ge
V/c
)t
dN
/dp
INE
L1
/N
-310
-210
-110
1
= 7 TeVspp at 2+stat2syserror=
Preliminary
Normalization Error 8.3%
-K
Phojet
Pythia D6T
Pythia Perugia0
Pythia Perugia 2011
(GeV/c)t
p0 0.5 1 1.5 2 2.5 3
MC
/data
0
0.5
1
1.5
2
K-‐ p
Best agreement with MC models for Pythia -‐ Perugia 2011 for Kaons at all pT and protons for pT>0.7 GeV/c, while pions are overes=mated at high pT.
π-‐
Iden=fied primary π/K/p spectra by combined analysis in ITS, TPC and TOF. See backup slides for posi=ve par=cles.
<pT> and ratios
14/03/12 F. Bellini, Rencontres de Moriond -‐ QCD 6
)2M (GeV/c0 0.2 0.4 0.6 0.8 1 1.2
(G
eV
/c)
! t p"
0
0.2
0.4
0.6
0.8
1
1.2
1.4 = 7 TeVsALICE, pp,
= 900 GeVsALICE, pp,
= 900 GeVsp, pUA5,
= 200 GeVsSTAR/PHENIX, pp,
# K p
ALICE preliminary = 7 TeVspp at
2+stat2syserror =
(GeV)s10 210 310
!K
/
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.16
0.18
ALICE ppSTAR ppNA49 ppPHENIX pp
pE735 ppUA5 p
ALICE preliminary = 7 TeVspp at
2+stat2syserror =
(GeV)s10 210 310
!p
/
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
-!/pALICE pp
+!ALICE pp p/
-!/pPHENIX pp
+!PHENIX pp p/
ALICE preliminary = 7 TeVspp at
2+stat2syserror = p/π
K/π
As collision energy increases, spectra get harder.
Mean pT increases linearly with hadron mass. K/π and p/π ra=os saturate between √s=0.9 and 7 TeV. p/π+ and p/π-‐ converge to the same value.
Resonances and comparison with models
14/03/12 F. Bellini, Rencontres de Moriond -‐ QCD 7
-1 (
Ge
V/c
)|y
|<0.8
|d
yT
dp
N2 d
evt
sN
1
-410
-310
-210 = 7 TeVspp INEL,
) / 2+
*!+ -
*!ALICE (
PHOJETPYTHIA D6T (109)
PYTHIA ATLAS-CSC (306)
PYTHIA Perugia 2011 (350)
ALICE Preliminary2 + syst2statuncert. =
) / 2+
*!+ -
*!(
(GeV/c)T
p0 0.5 1 1.5 2 2.5 3 3.5 4
0 0.5 1 1.5 2 2.5 3 3.5 4M
OD
EL / D
ATA
0
0.5
1
Models do not provide good descrip=on of resonance spectra yet.
Analysis exploits PID in TPC and TOF.
Yields extracted by fitting the spectra with a
Tsallis-Levy function.
(GeV/c)T
p0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5
-1 (
GeV
/c)
dy
Tdp
N2 d
evt
sN
1
-410
-310
-210
= 7 TeVs, pp !
= 0.9 TeVs, pp !
ALICE Preliminary
Φ(1020)
Multi-strange baryons and comparison with models
14/03/12 F. Bellini, Rencontres de Moriond -‐ QCD 8
-1 (
Ge
V/c
)|y
| <
0.5
dy
|t
N/d
p2
) d
inel.
evt
sN
!1
/(2 -6
10
-510
-410
-310
-"
-#
+"
+#
ALICE data 2010
= 7 TeVspp
2+syst2statUncert.:
ALICE Preliminary
vy FunctionseFitted with L
Normalization uncert.
(GeV/c)t
p0 1 2 3 4 5 6 7 8 9
Data
/ P
yth
ia P
20
11
2
4
Identification via “cascade” topology in ITS
+TPC, PID via dE/dx in TPC
Yields extracted by fitting the spectra with a
Tsallis-Levy function.
ALICE and CMS agree on Ξ . Difference due to different normaliza=on choice (INEL vs. NSD) Pythia – Perugia 2011 underes=mates the absolute values of yields, ⟨pT⟩and gain when going from √s = 0.2 to 7 TeV.
STAR, PRC 75, 064901 (2007) CMS, JHEP 05, 064 (2011)
dN/dy |(y~0) ~ s0.22 ,⟨pT⟩ ~ s0.25
0!
|y|
dN
/dy |
-410
-310
-210
pp collisions
, ALICE Inel±"
, CMS NSD±"
, STAR NSD±"
, PYTHIA Perugia 2011±"
, ALICE Inel±#
, STAR NSD±#
, PYTHIA Perugia 2011±#
(GeV) s210
310 410
> (
Ge
V/c
)t
<p
0.4
0.6
0.8
1
1.2
1.4
RHIC200 GeV
LHC900 GeV
LHC7 TeV
ALICE Preliminary
Ξ Ω
Summary - pp collisions
14/03/12 F. Bellini, Rencontres de Moriond -‐ QCD 9
• π/K/p, resonances and mul=-‐strange baryon spectra have been measured with ALICE down to low pT
• Comparison with Monte Carlo models show that Pythia -‐ Perugia 2011 tune
provides the best agreement for – Kaons and protons yields
but s=ll it is not sufficient to describe – Charged pions spectra at high pT (overes=mate) – Resonances spectra (underes=mate) – Mul=-‐strange baryons yields (underes=mate)
References for Pb-‐Pb collision available More effort needed to tune properly MC models
Medium evolution and “soft” probes
Hadronic states provide many useful observables to characterize medium produced
in ultra-relativistic heavy ion collisions
14/03/12 F. Bellini, Rencontres de Moriond -‐ QCD 11
Kine=c freeze-‐out – Stop elas=c interac=ons
Resonances re-‐scaqering and regenera=on
Chemical freeze-‐out -‐ Stop inelas=c interac=ons -‐ Fix par=cle ra=os
Thermaliza=on (hydrodynamics) -‐ Flow
Quark-‐Gluon Plasma forma=on (τ ~ 1 fm/c aser collision)
Pre-‐equilibrium state
Parton hard scaqering/Jets -‐ pQCD regime -‐ Hard probes
QGP expansion (life=me @ LHC ~ fm/c) -‐ Hadroniza=on
0-‐5% most central
80-‐90% peripheral
Centrality
Primary π/K/p spectra from RHIC to LHC
14/03/12 F. Bellini, Rencontres de Moriond -‐ QCD 12
!/dch
dN210 310
(G
eV
/c)
"T
p#
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2 (ALICE)-$ (ALICE)
-K
(ALICE)p (STAR Au-Au 200 GeV)-$ (STAR Au-Au 200 GeV)
-K
(STAR Au-Au 200 GeV)pALICE Preliminary
= 2.76 TeVNNsPb-Pb
2syst% + 2
stat%
(GeV/c)T
p0 0.5 1 1.5 2 2.5 3
-1d
y) (
Ge
V/c
)T
N/(
dp
2 d
-110
1
10
210
310
0-5% most centralALICE Preliminary
= 2.76 TeVNNsALICE, Pb-Pb,
= 200 GeVNNsSTAR, Au-Au, = 200 GeVNNsPHENIX, Au-Au,
S0
K -!
-K p
Nega9ve par9cles
STAR, PRC 79, 034909 (2009) PHENIX, PRC 69, 03409 (2004)
Harder spectra and flaqer protons than at RHIC <pT> increases with dNch /dη <pT> higher than at RHIC for similar dNch /dη
Indica=ons for stronger radial flow at LHC
π/K/p spectra testing hydrodynamic models
14/03/12 F. Bellini, Rencontres de Moriond -‐ QCD 13
(GeV/c)T
p0 0.5 1 1.5 2 2.5 3
-1d
y) (
Ge
V/c
)T
N/(
dp
2 d
-110
1
10
210
310
0-5% most centralALICE Preliminary
Curves: Hydro (arXiv:1105.3226)
= 2.76 TeVNNsALICE, Pb-Pb, S0
K +!
+K p
Posi9ve par9cles
(GeV/c)T
p0 0.5 1 1.5 2 2.5 3
-1dy
) (G
eV/c
)T
N/(d
p2 d
-110
1
10
210
310
0-5% most centralALICE Preliminary
Curves: Hydro + UrQMD (VISHNU) = 2.76 TeVNNsALICE, Pb-Pb, S
0K + +K p
Posi9ve par9cles
Hydro → UrQMD: decoupling temperature tuned to STAR p/π Hydro+UrQMD describes proton yield beUer than pure hydro.
Model: U.Heinz et al, arXiv:1105.3226 Model: U.Heinz et al, arXiv: 1108.5323
Yields and shape of π and K are in good agreement with hydro predic=ons.
Blast-wave fit to π/K/p spectra
14/03/12 F. Bellini, Rencontres de Moriond -‐ QCD 14
> (c)<0 0.2 0.4 0.6
(GeV
)foT
0
0.05
0.1
0.15
0.2, K, pAu-Au, pp, 0.2 TeV,
, K, pPb-Pb, 2.76 TeV,
Preliminary
Global Blast-‐wave fit to extract (kine=c) freeze-‐out temperature (Tfo) and average radial flow ‹β›
Tfo parameter of the model depends on π fit range. Resonances effect to be inves=gated
Schnedermann et al., Phys. Rev. C 48, 2462 (1993) STAR, PRC 79, 034909 (2009)
‹β› ≃0.66 c ~10% higher than at RHIC
Tfo seems slightly lower than at RHIC
Multi-strange baryons spectra
14/03/12 F. Bellini, Rencontres de Moriond -‐ QCD 15
(GeV/c)T
p0 1 2 3 4 5 6 7 8 9
-1 (
Ge
V/c
)|y
|<0.5
|T
dN
/dp
evt
s1
/N
-610
-510
-410
-310
-210
-110
1
10 = 2.76 TeVNNsPb-Pb at
2 + sys2staterror =
+!
0-20%
20-40%
40-60%
60-90%
Preliminary
(GeV/c)T
p0 1 2 3 4 5 6 7 8
-1 (
Ge
V/c
)|y
|<0.5
|T
dN
/dp
evt
s1
/N
-610
-510
-410
-310
-210
-110
1 = 2.76 TeVNNsPb-Pb at
2 + sys2staterror =
+!
0-20%
20-40%
40-60%
60-90%
Preliminary
An=-‐par=cle/par=cle ra=o ~ 1 also for mul=-‐strange baryons, as expected.
(GeV/c)T
p0 1 2 3 4 5 6 7 8 9 10
-1 (G
eV/c
)|y
|<0.
5 | T
dN
/dp
evts
1/N
-610
-510
-410
-310
-210
-110
1 = 2.76 TeVNNsPb-Pb at 0-90% centrality
2 + sys2staterror =
-
+
-
+
Preliminary
Spectra for mul=-‐strange par=cles measured in: • 0-‐90 % centrality • 4 centrality bins for Ξ and Ω (both charges) Iden=fica=on via “cascade” decay topology
Particle ratios testing the thermal model
14/03/12 F. Bellini, Rencontres de Moriond -‐ QCD 16
Model main assump=on: grand canonical descrip=on (also for Kaons and mul=-‐strange par=cles)
A.Andronic et al, Phys.LeE.B 673, 142 (2009)
Par=cle ra=os are (partly) in agreement with thermal model predic=ons
Protons difficult to fit in a thermal model with T = 160-‐170 MeV Ad hoc model with T = 148 MeV describes beUer p but fails for mul9-‐strange
At LHC an=-‐par=cle/par=cle ra=os at mid-‐rapidity are compa=ble with 1, as expected. à μB ~ 0
Λ/K0s from pp to Pb-Pb, from RHIC to LHC
14/03/12 F. Bellini, Rencontres de Moriond -‐ QCD 17
(GeV/c)T
p0 1 2 3 4 5 6 7 8
0 S /
K!
0
0.5
1
1.5
2
2.5
3 = 2.76 TeV, |y|<0.75NNsPb-Pb at
data points include stat. errorsestimated syst. error ~10 %
!/! "STAR: Au-Au 200 GeV
ALICE:
with 10% feed-down correction
0-5% centrality60-80% centrality 0-5% centrality60-80% centrality
Preliminary
(GeV/c)T
p0 1 2 3 4 5 6 7 8
S0 /
K!
0
0.5
1
1.5
2
2.5
0-5 % centrality20-40 % centrality40-60 % centrality60-80 % centrality80-90 % centrality
= 7 TeV)s(pp at = 0.9 TeV)s(pp at
data points include stat. errorsestimated syst. error ~10 %
Preliminary
= 2.76 TeV, |y|<0.75NNsPb-Pb at
Baryon/meson vs. pT increases from pp to a value above 1 for central Pb-‐Pb collisions Magnitude decreases from central to peripheral events, where it reaches pp ra=o. Radial flow (pT) shis when compared with STAR. Λ/K0s Magnitude increases with both centrality and beam energy from RHIC to LHC
Nuclear modifica9on factor defined as <Ncoll> = total number of binary nucleon-‐nucleon collisions (from a Glauber model)
Nuclear modification factor of Λ and K0s
14/03/12 F. Bellini, Rencontres de Moriond -‐ QCD 18
Suppression of strange baryon and meson measured in Pb-‐Pb collisions with respect to pp (here for most central collisions): Λ: baryon enhancement at intermediate pT and suppression at high pT K0s: meson suppression up to high pT For central collisions and high pT(> 8 GeV/c), the RAA of K0s and Λ is compa=ble with the one of charged par=cles
No strong flavor dependence of RAA is observed
(GeV/c)T
p0 5 10 15 20
AA
R
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6 = 2.76 TeV, 0 - 5 %sALICE, Pb-Pb,
, | y | < 0.750K
, | y | < 0.750!
| < 0.8"unidentified charged particles, |
, | y | < 0.8-# + +#
ALICE Preliminary
Strangeness enhancement
14/03/12 F. Bellini, Rencontres de Moriond -‐ QCD 19
>part<N1 10 210
> r
ela
tive
to
pp
part
Yie
ld / <
N
1
10
Preliminary
= 2.76 TeVNN
sPb-Pb at
-!
>part<N1 10 210
> r
ela
tive
to
pp
part
Yie
ld / <
N1
10
+"+
-"
+!
Enhancement increases following hierarchy of strangeness content (valence quarks) of baryons.
Strangeness enhancement with respect to pp collisions defined as:
Strangeness enhancement
14/03/12 F. Bellini, Rencontres de Moriond -‐ QCD 20
ALICE results compared with lower energy data (SPS, RHIC): • enhancement decreases as energy increases • same trend observed from RHIC to SPS Details of centrality dependence and energy dependence are work in progress..
Enhancement increases following hierarchy of strangeness content (valence quarks) of baryons.
Strangeness enhancement with respect to pp collisions defined as:
>part<N1 10 210
> r
ela
tive
to
pp
/Be
part
Yie
ld / <
N
1
10
Preliminary
= 2.76 TeVNN
sPb-Pb at
-!
"
NA57 (17.2 GeV):
STAR (200 GeV):
>part<N1 10 210
> r
ela
tive
to
pp
/Be
part
Yie
ld / <
N1
10
+#+
-#
+!
"
NA57 (17.2 GeV):
STAR (200 GeV):
Summary and conclusions - Pb-Pb collisions
14/03/12 F. Bellini, Rencontres de Moriond -‐ QCD 21
• π/K/p and mul=-‐strange baryon spectra have been measured for different centrality and compared to measurements at lower energies
• π/K/p, spectra mass and centrality dependence indicate a stronger radial flow at the LHC than at RHIC
• An9-‐par9cle/par9cle ra9o ~ 1, as expected à μB~0 at LHC • Ra9os of Ξ, Ω, K to π compa9ble with thermal model expecta9ons • p/π difficult to understand in a thermal model prediction with T=160-170 MeV
• Strange baryon/meson ra9o vs. pT increases from pp to a value above unity for central Pb-‐Pb
• Suppression of strange par9cle (RAA) produc=on shows no obvious flavor dependence
• Strangeness enhancement observed
ALICE provides many observables to characterize the medium evolu=on and proper=es at the LHC These were only selected highlights of the “sos” side of the story…
some more in the other presenta=ons at this conference !!!
Identified particles pT-spectra analysis - details
14/03/12 F. Bellini, Rencontres de Moriond -‐ QCD 23
Events with primary vertex reliably measured by the SPD Primary tracks are selected. ITS: Primary vertex reconstruction (SPD) + Standalone tracking
PID via measurement of dE/dx in silicon dE/dx resolution: ~10-15% in PbPb TPC:
Global tracking PID via measurement of DE/dx in gas dE/dx resolution: ~5 % in Pb-Pb
TOF:
PID via gaussian unfolding of TOF signal
Global* time resolution: 80 ps in Pb-Pb
*Includes resolution on event time zero determination
p (GeV/c)0.2 0.3 1 2 3 4 5 6 7 10 20
TPC
sig
nal (
arb.
uni
ts)
50
100
150
200
e
K p d
ALICE Performance = 2.76 TeV min. biasNNsPb-Pb, 18/05/2011
π/K/p spectra in pp collisions at √s = 0.9 TeV
14/03/12 F. Bellini, Rencontres de Moriond -‐ QCD 24
pp at √s = 0.9 TeV Total pt-‐dependent error (syst. + stat.) Normaliza=on error 3.6%
pp at √s = 0.9 TeV Total pt-‐dependent error (syst. + stat.) Normaliza=on error 3.6%
Eur. Phys. J. C (2011) 71:1655
Different PID techniques exploited
Combined analysis in ITS, TPC and TOF
Min. pT = 0.1 (π), 0.2 (K) and 0.3 (p) GeV/c
Spectra have been fitted with Tsallis-Levy function in order to extract mean pT , particle yields and compute particle ratios.
π/K/p spectra in pp collisions at √s = 7 TeV
14/03/12 F. Bellini, Rencontres de Moriond -‐ QCD 25
Spectra have been fitted with Tsallis-Levy function in order to extract mean pT , particle yields and compute particle ratios.
(GeV/c)t
p0 0.5 1 1.5 2 2.5
-1 |
y|<
0.5
(G
eV
/c)
t d
N/d
pIN
EL
1/N
-310
-210
-110
1
10ALICE preliminary
= 7 TeVspp at
2+stat2syserror =
Levy fit
-!
-K
p
Normaliztion Error 8.3%
Nega9ve Total pt-‐dependent error (syst. + stat.)
Different PID techniques exploited
Combined analysis in ITS, TPC and TOF
Min. pT = 0.1 (π), 0.2 (K) and 0.3 (p) GeV/c
(GeV/c)t
p0 0.5 1 1.5 2 2.5
-1 |y
|<0.
5 (G
eV/c
)t
dN
/dp
INEL
1/N
-310
-210
-110
1
10ALICE preliminary
= 7 TeVspp at 2+stat2syserror =
Levy fit
+
+K
p
Normaliztion Error 8.3%
Posi9ve Total pt-‐dependent error (syst + stat.) shown
Measured spectra in pp@7TeV vs. models
K+ p -1 |y|
<0
.5 (
Ge
V/c
)t
dN
/dp
INE
L1
/N
-310
-210
-110
1
= 7 TeVspp at 2+stat2syserror=
Preliminary
Normalization Error 8.3%
+K
Phojet
Pythia D6T
Pythia Perugia0
Pythia Perugia 2011
(GeV/c)t
p0 0.5 1 1.5 2 2.5 3
MC
/data
0
0.5
1
1.5
2
-1 |y|
<0
.5 (
Ge
V/c
)t
dN
/dp
INE
L1
/N
-310
-210
-110
= 7 TeVspp at 2+stat2syserror=
Preliminary
Normalization Error 8.3%
p
Phojet
Pythia D6T
Pythia Perugia0
Pythia Perugia 2011
(GeV/c)t
p0 0.5 1 1.5 2 2.5 3
MC
/data
0
0.5
1
1.5
2
K-‐ p -1 |y|<
0.5
(G
eV
/c)
tdN
/dp
INE
L1/N
-310
-210
-110
= 7 TeVspp at 2+stat2syserror=
Preliminary
Normalization Error 8.3%
p
Phojet
Pythia D6T
Pythia Perugia0
Pythia Perugia 2011
(GeV/c)t
p0 0.5 1 1.5 2 2.5 3
MC
/data
0
0.5
1
1.5
2
-1 |y|
<0
.5 (
Ge
V/c
)t
dN
/dp
INE
L1
/N
-310
-210
-110
1
= 7 TeVspp at 2+stat2syserror=
Preliminary
Normalization Error 8.3%
-K
Phojet
Pythia D6T
Pythia Perugia0
Pythia Perugia 2011
(GeV/c)t
p0 0.5 1 1.5 2 2.5 3
MC
/data
0
0.5
1
1.5
2
14/03/12 F. Bellini, Rencontres de Moriond -‐ QCD 26
π/K/p spectra in Pb-Pb collisions at √sNN = 2.76 TeV
14/03/12 F. Bellini, Rencontres de Moriond -‐ QCD 27
(GeV/c)T
p0 0.5 1 1.5 2 2.5 3
(c/G
eV
)T
dyd
pN2
d
-110
1
10
210
310
0-5%
5-10%
10-20%
20-30%
30-40%
40-50%
50-60%
60-70%
-!
|y| < 0.5
2syst" + 2
stat"
(GeV/c)T
p0 0.5 1 1.5 2 2.5 3
(c
/Ge
V)
Td
yd
pN2
d
-210
-110
1
10
210
0-5%
5-10%
10-20%
20-30%
30-40%
40-50%
50-60%
60-70%
p
|y| < 0.5
2syst! + 2
stat!
(GeV/c)T
p0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2
(c/G
eV
)T
dyd
pN2
d
-110
1
10
210
0-5%
5-10%
10-20%
20-30%
30-40%
40-50%
50-60%
60-70%
-K
|y| < 0.5
2syst! + 2
stat!
(GeV/c)T
p0 0.5 1 1.5 2 2.5 3
(c/G
eV
)T
dyd
pN2
d
-110
1
10
210
310
0-5%
5-10%
10-20%
20-30%
30-40%
40-50%
50-60%
60-70%
+!
|y| < 0.5
2syst" + 2
stat"
(GeV/c)T
p0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2
(c
/Ge
V)
Td
yd
pN2
d
-110
1
10
210
0-5%
5-10%
10-20%
20-30%
30-40%
40-50%
50-60%
60-70%
+K
|y| < 0.5
2syst! + 2
stat!
(GeV/c)T
p0 0.5 1 1.5 2 2.5 3
(c/G
eV
)T
dyd
pN2
d
-210
-110
1
10
210
0-5%
5-10%
10-20%
20-30%
30-40%
40-50%
50-60%
60-70%
p
|y| < 0.5
2syst! + 2
stat!
Blast-‐wave fit to extract mean pT and integrated par=cle yields
(GeV/c)T
p0 0.5 1 1.5 2 2.5 3
-1dy)
(G
eV
/c)
TN
/(dp
2 d
-110
1
10
210
310
0-5% most centralALICE Preliminary
= 2.76 TeVNNsALICE, Pb-Pb,
= 200 GeVNNsSTAR, Au-Au, = 200 GeVNNsPHENIX, Au-Au,
STAR (TOF, feed-down corr.)
S0
K +!
+K p
(GeV/c)T
p0 0.5 1 1.5 2 2.5 3
-1d
y) (
Ge
V/c
)T
N/(
dp
2 d-110
1
10
210
310
0-5% most centralALICE Preliminary
= 2.76 TeVNNsALICE, Pb-Pb,
= 200 GeVNNsSTAR, Au-Au, = 200 GeVNNsPHENIX, Au-Au,
S0
K -!
-K p
14/03/12 F. Bellini, Rencontres de Moriond -‐ QCD 28
Measured spectra in Pb-Pb at LHC vs RHIC
Particle ratios in Pb-Pb collisions
14/03/12 F. Bellini, Rencontres de Moriond -‐ QCD 29
At LHC an=-‐par=cle/par=cle ra=os at mid-‐rapidity are compa=ble with 1, as expected for μB ~ 0. K/π and p/π ra=os at LHC and RHIC exhibit similar centrality dependence. K/π slightly increases with dNch/dη from pp to very central events
+!/-!
+/K
-K /pp
0.5
0.6
0.7
0.8
0.9
1
1.1
1.2
1.3
= 2.76 TeV (ALICE Pb-Pb)NN
s
= 200 GeV (STAR Au-Au)NN
s
= 200 GeV (PHENIX Au-Au)NN
s
ALICE Preliminary
0-5% centrality
!/dch
dN210 310
-"/-
K
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.16
0.18
0.2
= 2.76 TeVNNsALICE Pb-Pb
= 200 GeVNNsSTAR Au-Au ALICE Preliminary = 2.76 TeVNNsPb-Pb
2syst# + 2
stat#
= 7 TeVspp,
!/dch
dN210 310
-"/
p
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.16
0.18
0.2 = 2.76 TeV (feed-down corrected)NNsALICE Pb-Pb
= 200 GeV (not feed-down corrected)NNsSTAR Au-Au
= 200 GeV (feed-down corrected)NNsPHENIX Au-Au
= 200 GeV (feed-down corrected, stat. errors only)NNsBRAHMS Au-Au
ALICE Preliminary
= 2.76 TeVNNsPb-Pb
2syst# + 2
stat#
= 7 TeVspp,
STAR, not feed-‐down subtracted
STAR, PRC 79, 034909 (2009) PHENIX, PRC 69, 03409 (2004) BRAHMS, PRC 72, 014908 (2005)
Feed-down correction for p for pp analysis
Feed-down correction needed to eliminate contributions from weak decay of strange particle (Λ,Ξ,…) to the primary spectra:
• for protons ~40% • for pions ~15%
Distance of closest approach (DCA) in the bending plane used to correct. Correction estimated from a fit using Monte Carlo templates for distributions of • primaries • secondaries from weak decay of strange
particles • secondaries from interaction with the
material.
14/03/12 F. Bellini, Rencontres de Moriond -‐ QCD 30
Global tracks, TPC PID (0.45 < pT < 0.50 GeV/c)
• ITS vertexing + tracking • TPC tracking + PID (dE/dx) • Topological reconstruction of decays:
– Selection of Λ based on cuts on impact
parameter and invariant mass – TPC PID for all decays products
• Signal extraction: – Polynomial+gaussian fit for mean and σ – Bin counting in (±3σ) signal region – Integral of background fit function in signal
region – Signal = bin counting - integral
Multi-strange baryons analysis ALICE Physics Performance Report vol. II
HIJING Pb-‐Pb event at √sNN = 5.5 TeV
π-‐ Λ π-‐
p
Ξ-‐
14/03/12 F. Bellini, Rencontres de Moriond -‐ QCD 31
Centrality in Pb-Pb collisions
14/03/12 F. Bellini, Rencontres de Moriond -‐ QCD 32
0-‐5% most central
80-‐90% peripheral
The collision centrality is determined using the total mul=plicity detected in the forward VZERO detectors and reported as a frac=on of the total hadronic cross sec=on.
ALICE, PRL 106, 032301 (2011)
Nuclear modification factor of Λ and K0s
14/03/12 F. Bellini, Rencontres de Moriond -‐ QCD 33
(GeV/c)T
p0 5 10 15 20
AA
R
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6 = 2.76 TeV, 0 - 5 %sALICE, Pb-Pb,
, | y | < 0.750K
, | y | < 0.750!
| < 0.8"unidentified charged particles, |
ALICE Preliminary
(GeV/c)T
p0 5 10 15 20
AAR
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6 = 2.76 TeV, 60 - 80 %sALICE, Pb-Pb,
, | y | < 0.750K, | y | < 0.750
| < 0.8unidentified charged particles, |
ALICE Preliminary
Suppression of strange baryon and meson measured in central (les) and peripheral (right) Pb-‐Pb collisions with respect to pp: Λ: baryon enhancement at intermediate pT , suppression at high pT K0s: meson suppression up to high pT
(GeV/c)T
p0 5 10 15 20
AA
R
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6 = 2.76 TeV, 60 - 80 %sALICE, Pb-Pb,
, | y | < 0.750K
, | y | < 0.750!
| < 0.8"unidentified charged particles, |
, | y | < 0.8-# + +#
ALICE Preliminary
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