lhc and search for higgs boson farhang amiri physics department weber state university farhang amiri...
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LHC and Search for Higgs Boson
Farhang AmiriPhysics Department
Weber State University
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Atoms
This arises because atoms have substructure
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Inside Atoms: neutrons, protons, electrons
Carbon (C )
Gold (Au)
Atomic number Z=6 (number of protons)
Mass number A=12 (number of protons + neutrons)
# electrons = # protons (count them!) (atom is electrically neutral)
Atomic number Z = 79
Mass number A = 197
#electrons = # protons (trust me!)
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Further layers of substructure: u quark: electric charge = 2/3
d quark: electric charge = -1/3
Proton = uud electric charge = 1
Neutron = udd electric charge = 0
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Fundamental Particles
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Force Strength
Carrier Physical effect
Strong nuclear 1 Gluons Binds nuclei
Electromagnetic .001 Photon Light, electricity
Weak nuclear .00001 Z0,W+,W- Radioactivity
Gravity 10-38 Graviton? Gravitation
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Young-Kee Kim: Ten Year Plan (Science and Resources), PAC Meeting 2009-03-0510
Tevatron ColliderMiniBooNESciBooNE
MINOS
250 kW at 120 GeVfor neutrinos
17 kW at 8 GeVfor neutrinosSoudan
The Intensity Frontier
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We make high energy particle interactions by colliding two beams heads on
Accelerators – powerful tools for particle physics
2 km
DZero Experiment
CDF Experiment
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Energy, Mass, and Speed
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Why Higgs Boson?
• Standard Model
• QCD (Quantum Chromodynamics)• QED (Quantum Electrodynamics)
Force Strength
Carrier Physical effect
Strong nuclear 1 Gluons Binds nuclei
Electromagnetic .001 Photon Light, electricity
Weak nuclear .00001 Z0,W+,W- Radioactivity
Gravity 10-38 Graviton? Gravitation
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Forces
• Strong, weak, electromagnetic, gravity
• Force carriers: gluon, W/Z bosons, photon• Gluon and photon are massless• W/Z are very heavy…..WHY?????
This is the question of symmetry breaking
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Why is Mass a Problem?
Gauge Invariance is the guiding principle• Gauge Invariance leads to QED
– Predicts massless photons• Gauge Invariance leads to QCD
– Predicts massless gluons• Applying the same principle to weak
interactions, predicts massless force carriers (i.e. W/Z)
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The Solution: The Higgs Field
• Screening Current– Photons behave as if they have mass– This idea could be responsible for the mass of force-field
quanta
The relationship between screening current and mass, and in the context of quantum field theory was developed by Peter Higgs (1964).
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Higgs Field
• We hypothesize that there is a background density of some field with which W and Z quanta interact (but not the massless photon).
• The interaction of W+, W-, and Z with Higgs field leads to the screening effect and generates the effective masses of these particles.
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Higgs Boson
• In order to give a nonzero value to the background field, we need a Higgs potential.
• Deviations from the uniform field values at different points in space-time, indicates the presence of quantum of this field, that is, the Higgs Boson.
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Producing Higgs Bosons
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Producing Higgs Bosons
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Gluon-gluon fusion
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How to Discover Higgs
• This is a tricky business!– Lots of complicated statistical tools needed at some level
• But in a nutshell:– Need to show that we have a signal that is inconsistent with being
background
– Need number of observed data events to be inconsistent with background fluctuation
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Higgs Boson Decay
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If a Higgs particle is produced in a proton-proton collision, an LHC detector might infer what you see here. The four straight red lines indicate very high-energy particles
(muons) that are the remnants of the disintegrating Higgs.
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Status of Higgs Before LHC
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ATLAS Results
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Higgs Searches in ATLAS•The Higgs boson can decay into a variety of different particles
•ATLAS currently covers nine different decay modes.
•The latest data: 85% of all mass regions below 466 GeV are excluded at the 95% CL.
•Higgs discovery is most likely: 115-146 GeV, 232-256 GeV, 282-296 GeV plus any mass above 466 GeV.
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