The Big Bang, the LHC and the Higgs Boson
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Transcript of The Big Bang, the LHC and the Higgs Boson
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The Big Bang, the LHC and the Higgs Boson
Dr Cormac O’ Raifeartaigh (WIT)
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Overview
I. LHC
What, How and Why
II. Particle physicsThe Standard Model
III. LHC Expectations
The Higgs boson and beyond
Big Bang cosmology
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The Large Hadron Collider
No black holes
High-energy proton beams
Opposite directions
Huge energy of collision
Create short-lived particles
E = mc2 Detection and measurement
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How
E = 14 TeV
λ =1 x 10-19 m
Ultra high vacuum
Low temp: 1.6 K
LEP tunnel: 27 km 1200 superconducting magnets
600 M collisions/sec
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Why
Explore fundamental constituents of matter
Investigate inter-relation of forces that hold matter together
Glimpse of early universeHighest energy since BB
Mystery of dark matter Mystery of antimatter
T = 1019 K
t = 1x10-12 s
V = football
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Cosmology
E = kT → T =
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Particle cosmology
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Particle detectors
4 main detectors
• CMS multi-purpose
•ATLAS multi-purpose
•ALICE quark-gluon plasma
•LHC-b antimatter decay
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Particle detectors
Tracking devicemeasures momentum of charged particle
Calorimeter measures energy of particle by
absorption
Identification detector measures velocity of particle by Cherenkov radiation
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II Particle physics (1930s)
• electron (1895)
• proton (1909)
• nuclear atom (1911)RBS
• what holds nucleus together?• what holds electrons in place?• what causes radioactivity?
Periodic Table: protons (1918)
• neutron (1932)
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Four forces of nature Force of gravityHolds cosmos togetherLong range
Electromagnetic force Holds atoms together
Strong nuclear force: holds nucleus together
Weak nuclear force: Beta decay
The atom
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Strong force
SF >> em
charge indep
protons, neutrons
short range
HUP
massive particle
Yukawa pion
3 charge states
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New particles (1950s)
Cosmic rays Particle accelerators
cyclotronπ + → μ + + ν
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Particle Zoo (1960s)
Over 100 particles
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Quarks (1960s)
new periodic tablep+,n not fundamental symmetry arguments
(SU3 gauge symmetry)
SU3 → quarksnew fundamental particlesUP and DOWNprediction of -
Stanford experiments 1969
Gell-Mann, Zweig
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Quantum chromodynamics
scattering experiments
colour
SF = chromodynamics
asymptotic freedom
confinement
infra-red slavery
The energy required to produce a separation far exceeds the pair production energy of a quark-antiquark pair,
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Quark generations
Six different quarks(u,d,s,c,t,b)
Six leptons
(e, μ, τ, υe, υμ, υτ)
Gen I: all of matter
Gen II, III redundant
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Electro-weak interaction
Gauge theory of em and w interaction
Salaam, Weinberg, Glashow
Above 100 GeV
Interactions of leptons by exchange of W,Z bosons
Higgs mechanism to generate mass
Predictions• Weak neutral currents (1973)• W and Z gauge bosons (CERN, 1983)• Higgs boson
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The Origin of MassThe strong nuclear force cannot explain the mass of the electron though…
The Higgs BosonWe suspect the vacuum is full of another sort of matter that is responsible – the higgs…. a new sort of matter – a scalar?
Or very heavy quarks top mass = 175 proton mass
To explain the W mass the higgs vacuum must be 100 times denser than nuclear matter!!
It must be weak charged but not electrically charged
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The Standard Model (1970s)
Strong force = quark force (QCD)
EM + weak force = electroweak
Matter particles: fermions
(quarks and leptons)
Force particles: bosons
Prediction: W+-,Z0 boson
Detected: CERN, 1983
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Standard Model : 1980s
• Experimental success but Higgs boson outstanding
Key particle: too heavy?
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III LHC expectations (SM)
Higgs boson
Determines mass of other particles
120-180 GeV
Set by mass of top quark, Z boson
Search…surprise?
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Main production mechanisms of the Higgs at the LHC
Ref: A. Djouadi,hep-ph/0503172
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For low Higgs mass mh 150 GeV, the Higgs mostly decays to two b-quarks, two tau leptons, two gluons and etc.
In hadron colliders these modes are difficult to extract because of the large QCD jet background.
The silver detection mode in this mass range is the two photons mode: h , which like the gluon fusion is a loop-induced process.
Higgs decay channels
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Decay channels depend on the Higgs mass:
Ref: A. Djouadi, hep-ph/0503172
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Ref: hep-ph/0208209
A summary plot:
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Expectations: Beyond the SM
Unified field theory
Grand unified theory (GUT): 3 forces
Theory of everything (TOE): 4 forces
Supersymmetry
symmetry of fermions and bosons
improves GUT
makes TOE possible
Phenomenology
Supersymmetric particles?
Not observed: broken symmetry
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IV Expectations: cosmology
√ 1. Exotic particles:S
√ 2. Unification of forces
3. Nature of dark matter?neutralinos?
4. Missing antimatter? LHCb
High E = photo of early U
1. Unification of forces: SUSY
2. SUSY = dark matter? double whammy
3. Matter/antimatter asymmetry?
LHCb
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Particle cosmology
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LHCb
Tangential to ringB-meson collectionDecay of b quark, antiquarkCP violation (UCD group)
• Where is antimatter?• Asymmetry in M/AM decay• CP violation
Quantum loops
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SummaryHiggs bosonClose chapter on SM
Supersymmetric particlesOpen new chapter: TOE
CosmologyNature of Dark MatterMissing antimatter
Unexpected particles?New avenues
http://coraifeartaigh.wordpress.com
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Epilogue: CERN and Ireland
World leader
20 member states
10 associate states
80 nations, 500 univ.
Ireland not a member
No particle physics in Ireland
European Organization for Nuclear Research