From Theory To History:

Christian SmithCharles Jay

Jeremy UmphressRobert Farrar

Physics 3313-001Dr. Jaehoon YuUniversity of Texas at ArlingtonDecember 4, 2013

The Discovery of the Higgs Boson

http://www.symmetrymagazine.org/article/october-2013/nobel-prize-in-physics-honors-prediction-of-higgs-boson

Today’s Presentation:• The History of the Higgs Particle

• The need for broken symmetry• The Higgs mechanism as the solution• Complications with theory

• Experimental Process• How to look for the Higgs• Zoning in on the mass of the Higgs• Criterion for the Higgs• Discovery of the Higgs boson

• The Discovery and Future• What this discovery means for Physics• What is next?

Why Do We Need Broken Symmetry?• If everything were symmetric, all the particles would

be canceled out by their anti-particles.

• The imbalance allows the existence of the particles that constitute our existence.

• What breaks this symmetry of particle – anti-particle creation?

The Higgs Mechanism• The original theory of broken symmetry was proposed by

Sheldon Glashow in 1960. Though he was unsure of what caused this breakage.

• “The mass of the charged intermediaries must be greater than the K-meson mass, but the photon mass is zero-surely this is the principle stumbling block in any pursuit of the analogy between hypothetical vector mesons and photons. It is a stumbling block we must overlook.” (Glashow)

• Roughly four years later Higgs, Englert and Brout propose a mechanism that would account for this breaking of symmetry.

The Higgs Mechanism (cont.)• In the standard model of Physics all our elementary particles are

massless. • We know from experimentation that they have mass, where does this

mass come from?

• Higgs-Englert-Brout Mechanism would give these particles their mass, thus allowing for the breaking of symmetry.

• How do the objects interact with the Higgs field?

• How do they obtain their mass from this field?

The Higgs Mechanism (cont.)• At the Big Bang, all the fundamental particles were pure energy.

• Within the first second, the universe cooled and the Higgs field was formed.

• Each of the fundamental particles interact with this field differently, slowing them down.

• The greater the interaction with the Higgs field, the greater the mass.

• Particles like photons and gluons do not interact with the Higgs field, while W and Z bosons and top quarks interact heavily with the Higgs Field.

Complications With The Theory

• Though the mechanism had been proposed, the Higgs field must have an associated particle in order to observe its existence.

• The mass of this particle was not determined in the theory, which means that the mass of the Higgs boson could vary widely.

How To Generate A Higgs

http://news.softpedia.com/newsImage/World-039-s-Largest-Physics-Experiment-Hopes-to-Catch-a-Glimpse-of-the-Big-Bang-2.jpg/

• Particles must be massive enough to have enough energy to form Higgs Bosons.

• Top Quarks are the preferred particles, but are not commonly found in nature.

• Top quarks can be formed through the collision of gluons.

• Gluons and up and down quarks are found in protons, so by the collision of protons we can collide gluons.

• How do we see the Higgs?

Higgs Production• Two gluons are collided to form top

quarks which are then used to generate a Higgs.

• Higgs decays into W-boson pair. Which then decays to photons.

• Higgs decays in bottom quark pair. Which then decays to photons.

http://www.nature.com/nphys/journal/v9/n5/fig_tab/nphys2619_F1.html

How To Look For The Higgs (cont.)

http://cds.cern.ch/record/1406057

• Accounting for events and what could generate them.

• Formation of γ γ , photon pairs. (UC Berkley)

• Formation of 4 electrons or muons. (UC Berkley)

• Formation of W-Boson Pairs. (Dreiner)

• Determining the mass of the particle that would generate the different events.

• Ruling out known particles that would generate other events.

• Looking for the “anomaly.” (BBC)

The Possible Mass Of The Higgs

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 210

Possible Mass of Higgs Boson

Mass (GeV)

LEP (2003) FermiLab(2010)

LHC(2011)

The Anomaly

http://cms.web.cern.ch/news/observation-new-particle-mass-125-gev

• 2012 data run was focused in the mass range between 114 GeV and 145 GeV.

• Data collected from both CMS (Bottom Left)

and ATLAS (Bottom Right) show anomalies between 120-130 GeV.

http://www.atlas.ch/HiggsResources/

Matching The Higgs To Results• Higgs must have enough mass to create a bottom quark pair,

photon pair or W-Boson pair.

• Higgs must have an integer spin of zero. So angular distribution of products is equally probable in all directions. (CERN)

• Must have positive parity. Does not distinguish between left and right. (CERN)

• Must be electrically neutral (unaffected by electric or magnetic fields).

Discovery Of The Higgs Particle• On July 04, 2012 CERN announced the results of the data

that had been collected between 2010-11 and analyzed.

• The ATLAS and CMS experiments independently observed statistical anomalies at 126 GeV (ATLAS) and 124 GeV (CMS).

• The results showed a 5-sigma standard deviation (1 in 350 million), this means that there was a 1 in 350 million possibility that the event was caused by background noise. (CMS-CERN)

Future Of The Higgs• Increase in our understanding of the fundamental

particles and their creation.

• Other theories propose the existence of multiple Higgs, leading into further exploration of nature.

• Coupling between matter and the Higgs and the Higgs and dark matter could allow for the observation of dark matter.

What We Have Covered Today• The History of the Higgs Particle

• The need for broken symmetry for the existence of particles.• The Higgs mechanism as the solution to break the symmetry• Complications with theory with the lack of mass of the Higgs

• Experimental Process• How to look for the Higgs by finding the results of its decompositions• Zoning in on the mass of the Higgs by various experiments• Criterion for the Higgs particle: spin, parity and mass• Discovery of a Higgs boson

• The Discovery and Future• Furthered understanding of nature• Study of dark matter and existence of other Higgs Bosons.

Q & A

Sources• Abbiendi, G, et al. “Search for the Standard Model Higgs Boson at LEP.” ALEPH, DELPHI, L3, OPAL

Collaborations. (2003)• BBC. Jan 09, 2012. “The Hunt For The Higgs.” http://www.youtube.com/watch?v=r4-wVzjnQRI • CERN Press Office. March 14, 2013. “New Results Indicate that particle discovered at CERN is a

Higgs boson.” http://press.web.cern.ch/press-releases/2013/03/new-results-indicate-particle-discovered-cern-higgs-boson

• CMS Experiment, CERN. July 04, 2012. http://cms.web.cern.ch/news/observation-new-particle-mass-125-gev

• Dreiner, H. “Particle Physics: A Higgs is a Higgs.” Nature Physics. NS-9. 268-9. (2013)• FermiLab Press Release. July 26, 2010. “FermiLab experiments narrow allowed mass range for

Higgs Boson.” http://www.fnal.gov/pub/presspass/press_releases/Higgs-mass-constraints-20100726.html

• FermiLab Press Release. August 22, 2011. “LHC experiments eliminate more Higgs hiding spots.” http://www.fnal.gov/pub/presspass/press_releases/2011/higgs-hiding-spots-20110822.html

• Glashow, S. “Partial Symmetries of Weak Interactions.” Nuclear Physics. NP-22. 579-588. (1961)• UC Berkley. July 13, 2012. “The Higgs Boson Explained.” http://

www.youtube.com/watch?v=jchDY6xuiZ0