HIGGS BOSON – THE GOD PARTICLETerm Paper: Nuclear Physics (PHYS-422)

Name: Jawad Kamran

Roll # 16-10946

B.Sc (hons) Physics

April 8, 2014.

Term Paper: PHYS-422 Higgs Boson – The God Particle Jawad Kamran

Introduction:

The Higgs Boson is an electrically neutral spin-0 elementary particle, first theorized in ‘1964PRL1 symmetry breaking papers’ by sixdifferent scientists in order toexplain Higgs mechanism. It wasannounced experimentally confirmedat CERN on March 14, 2013 by ATLASand CMS teams working on LHC2.

This paper aims to outline the history of Higgs theory, people and experiments involved inprediction and confirmation of HiggsBoson, significance and implicationsof this enormous discovery.

Historical background:The theories and discoveries of numerous physicists, which started in early 1930s resulted in the formulation and improvement of Standard model of Physics. It let to a significant understanding of elementary structure of matter:

(i) Everything in the universe, no matter how large or small, is formulated from a few basic elementary structures called fundamental particles.

(ii) These particles are governed by four fundamental forces.

Developed in the early 1970s, Standard model of Physics positively explains a large number of phenomena and is proved again and again by countless experiments.

Three of these fundamental forces originate due to the exchangeof force-carrying particles, which belong to a wider group of particles called “bosons”. Matter particles transfer distinct amounts of energy when they exchange bosons. Each fundamental force is related to a corresponding boson. The Standard Model

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Figure 1: Peter Higgs (Middle) shedding tears at the moment of announcement for confirmation of Higgs Boson, at CERN. © CERN

Term Paper: PHYS-422 Higgs Boson – The God Particle Jawad Kamran

of Physics encompasses the electromagnetic, strong and weak forces. It includes their carrier particles and also describes how these forces act on all other particles. Higgs Particle belongs to the same class of fundamental particles, known as Bosons. It is needed to be there due to a fundamental symmetry associated with mass origin theories where the force carriers are spin-1 bosons.

For the explanation of some disagreements in theories regardingorigin of mass, Higgs mechanism was developed in 1964 by three different groups of scientists. Higgs mechanism was merged intoparticle physics by Steven Weinberg and Abdus Salam, as a crucial part of the standard model. Hence, Higgs Boson is the particle first predicted by unified electroweak theory in Standard model of Physics.

1 PRL: Physics Review Letters2 LHC: Large Hadron ColliderSignificance of Higgs Boson:

Before the Higgs mechanism was modeled, it was not known how toframe a consistent relativistic field theory which could be comprise of both massless and massive force carrier particles and also has local symmetry. The mechanism, hence, gained the importance of a last brick in the wall of standard model. In order to prove the theory behind Higgs mechanism, Higgs boson must had been detected. It is produced as a result of excitation of Higgs field.  Higgs mechanism is crucial to explain the property "mass". This is a most-important property of almost all elementary particles. Hence, Higgs Boson gives answers to one the most fundamental questions of Physics; why most of fundamental particles have mass?

The nick name ‘God Particle’:

The term God particle for Higgs boson was coined first time by physicist Leon M. Lederman and science writer Dick Teresi in a

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Term Paper: PHYS-422 Higgs Boson – The God Particle Jawad Kamran

1993 book called “The God Particle: If the Universe Is the Answer, What Is the Question?”

The word ‘God’ at first give the sense of its importance and significance but its actual origin is rather interesting as Lederman explains in the book why he gave the Higgs boson the nickname "The God Particle":

“I have given it nickname: the God Particle. Why God Particle? For two reasons. One, the publisher wouldn't let it be called the Goddamn Particle, though that might have been a more appropriate title, given its elusive nature and the expense due to it. And two, there is a connection, of sorts, to another book1, a much older one...”

—p. 22

The particle now has acquired the name ‘God particle’ because of the reason the monumental questions about matter that the Higgs Bosom might be able to answer. The man who first proposedthe Higgs boson’s existence, Peter Higgs, isn’t very fond of the nickname “God particle” as he once said:

“First of all, I’m an atheist. The second thing is I know that name was kind of joke andnot a very good one. It is so misleading. I want people to stop referring to it as God Particle.”

—Telegraph

1 another book: The Book of Genesis

Hunt for Higgs Boson:

The quest to find the Higgs boson became a main aim of experimental particle physics. According to the best fit valuewhich the electroweak theory measurements gave, the mass of Higgs Boson should lie between 52 and 110 GeV.

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Term Paper: PHYS-422 Higgs Boson – The God Particle Jawad Kamran

Experimental Higgs searches are challenging for at least two reasons: the theoretically allowed mass range is large and the predicted Yukawa couplings to the fundamental fermions (quarks and leptons i.e. the essential components of colliding beams) are proportional to the fermion mass. For this reason, the probability for direct Higgs detection (i.e, reaction e+ + e-- =H0) at an electron-positron collider like LEP1 is very small.

LHC:

The energy range in which Higgs Boson was predicted to be founddelimited all particle accelerators, existed at the time, to find this particle. To develop a new and more powerful accelerator, countries, organizations, scientists and universities from all over the world collaborated to build LHC (Large Hadron Collider). It took nearly 10 years to construct (1998-2008) this most technologically advanced machine ever built on Swiss-French border. (Fig.2) This is the most expensive scientific project ever taken; with a budget of nearly $9 billion. As of 2014, the LHC is still the largest andmost complex facility ever built in the history of mankind for the sake of experimentation. LHC is the most powerful particle accelerator to date; it can make collisions of about 14TeV and identify their outcomes.

The LHC is made of a ring which is 27km in circumference. Superconducting magnets are present along the ring to boost theparticle’s energy during their motion.

Figure 2: LHC on Swiss-French border- © scienceblogs.com

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Term Paper: PHYS-422 Higgs Boson – The God Particle Jawad Kamran

Inside the accelerator, two particle beams travel in opposite direction at the speed close to that of light before they collide. They move in separate beam tubes – kept at very high vacuum. The beams are directed around the ring by a very strongmagnetic field which is due to those superconducting magnets. 1 LEP: Large Electron–Positron Collider

Figure 3: A section of LHC © CERN

The electromagnets are built from electric cable in the form ofcoils which works in a superconducting state, so that electricity is conducted efficiently without unnecessary energylosses. This requires cooling the magnets down to -271.3°C – a temperature colder than outer space. To fulfill this, the entire accelerator is connected to a vast system which deliversliquid helium so to cools the magnets and also other supply services.

The beams inside the LHC are made to collide at four locations around the accelerator ring, which correspond to the positions of four particle detectors – ATLAS, CMS, ALICE and LHCb. (Fig.4). ATLAS and CMS are dedicated to the search of Higgs Boson while ALICE is looking for quark-gluon plasma and LHCb isinvestigating the missing anti-matter after the big bang.

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Term Paper: PHYS-422 Higgs Boson – The God Particle Jawad Kamran

Figure 4: CAD model of ATLAS detector. It is 46 meters long, 25 meters in diameter, andweighs

about 7,000 tones; containing about 3000 km of cable © Stanford University

Detection of Higgs Boson:

In LHC, the Higgs boson is produced by a pp (proton) collision.

p + p = H0 +X (X: Any state allowed by conservation laws.)

The huge amount of recorded information allows the LHC experiments to pick out single pp collisions among the billionsof collisions when two accelerated proton beams with 1014

protons collide at the center of the detector every 50 ns.

For a Higgs boson with a mass of126 GeV/c2 the Standard model predicts a mean life time of about 1.6×10−22 s. After this time,the Higgs boson will decay further into different particles which are actually detected as a signature of the existence of Higgs boson.

Higgs boson disintegrates in 4l (leptons) decay as following. It first decays into Z-bosons and then finally in 4 leptons. (Fig.5)

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Term Paper: PHYS-422 Higgs Boson – The God Particle Jawad Kamran

𝐻0 → 𝑍 + 𝑍* + γ

𝑍 + 𝑍* + γ → 𝑙- + 𝑙 + + 𝑙- + 𝑙 +

Figure 5: 4 lepton decay of Higgs boson. At ATLAS detector. © CERN

Nobel Prize 2013:

The Nobel Prize in Physics 2013 wasawarded jointly to François Englert(Belgian) and Peter W. Higgs(British) "for the theoretical discovery of amechanism that contributes to ourunderstanding of the origin of mass ofsubatomic particles, and which recently wasconfirmed through the discovery of the predictedfundamental particle, by the ATLAS and CMS experiments at CERN's Large Hadron Collider"

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Figure 6: © nobleprize.org

Term Paper: PHYS-422 Higgs Boson – The God Particle Jawad Kamran

The noble for the Higgs boson was one of the most anticipated one in the history. It was announced the same year CERN confirmed the existence of Higgs Boson.

Some criticism on Nobel committee was seen from many scientistsas they suggested the work for other scientists on the same mechanism was ignored as the relativistic model was developed by three independent groups: by Robert Brout and François Englert; by Peter Higgs; and by Gerald Guralnik, C. R. Hagen, and Tom Kibble. They also suggested that there should’ve been some credit to CERN as an organization and 3000 scientists who worked there day and night for the search of Higgs Boson.

Higgs Boson ≠ Mass

It is a widely held idea, though wrong, that Higgs Boson is responsible for the mass around us. In fact, Higgs Boson is merely an evidence for a mechanism which explains why fundamental particles have masses. As an Australian physicist explains: Higgs Boson indicates that there is Higgs field whichpermeates through all space. When fundamental particles, say anelectron, interact with this field they get the property of mass. They field, in a way ‘slows the particles down’ which gives them mass and stops them from reaching the cosmic speed limit, i.e. of light.

If we look at particles like Proton and Neutrons, they are composed of quarks. Quarks being fundamental particles interactwith the Higgs field and hence have mass. But if the masses of quarks inside a nucleus are combined, they account to no more than 1% mass of the proton/neutron. Where is the rest of mass coming from? Answer lies in the Einstein’s famous equation E = mc2. The strong forces present inside a proton/neutron and gluons, which hold quarks together, actually give the rest of 99% of the mass. This is analogous to the concept of Mass

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Term Paper: PHYS-422 Higgs Boson – The God Particle Jawad Kamran

Defect of a nucleus where the mass of nuclei are not equal to combined masses of protons and neutrons.

Hence, most of the mass around us is by virtue of Strong Force holding the matter together at the very fundamental level. (m=E/c2).

Summary:

The extent of effort put by the individual scientists and organizations all over the world behind the idea of Higgs Bosonis a very good measure to evaluate its importance. Higgs boson validates the Standard model, explains symmetry breaking in electroweak interaction, and gives insight into the origin of mass. For this immense importance, the discovery is very huge to the entire scientific world. With this discovery, there is the ability to have huge implications in scientific advances especially in the theoretical understanding of the universe. The Higgs Boson has taken us one step further into our age old quest of finding the answer to the ultimate question: What is the nature of this universe?

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Term Paper: PHYS-422 Higgs Boson – The God Particle Jawad Kamran

Bibliography:

[1] Nobel Prize Org. http://www.nobelprize.org/nobel_prizes/physics/laureates/2013/

[2] CERN. http://home.web.cern.ch/about/physics/standard-model

[3] Martin, B.R (2006) “Nuclear and Particle Physics: An introduction” Chapter 9: ……Outstanding Questions and Future Prospects. Published by John Wiley and Sons, Ltd. The ……Atrium, Southern Gate, Chichester, West Sussex PO19 8SQ, England

[4] Science and Technology Facilities Council http://www.stfc.ac.uk/646.aspx

[5] Phys. Lett. B 726 (2013) 587 “Search for a Higgs boson decaying into a Z and a photon in ……pp collisions at sqrt(s) = 7 and 8 TeV” July21, 2013.

[6] “Scientific Background on the Nobel Prize in Physics 2013 - The Beh-Mechanism, … ……Interaction with short range forces and scalar particles” compiled by the class for Physics … …of the Royal Swedish academy of Sciences.

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Term Paper: PHYS-422 Higgs Boson – The God Particle Jawad Kamran

[7] Brief History of the Higgs Mechanism by University of Edinburgh. ……http://www.ph.ed.ac.uk/higgs/brief-history

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