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Walton, the LHC and the Higgs boson
Cormac O’Raifeartaigh (WIT)
Albert Einstein
Ernest Walton
Overview
I. LHC
What, why, how
II. A brief history of particles
From Walton to the Standard Model
III. LHC Expectations
The Higgs boson
Beyond the Standard Model
Particle cosmology
The Large Hadron Collider (CERN)
High-energy proton beams
Head-on collision
Huge energy density
Create short-lived particles
E = mc2
Detection and measurement
No black holes
Why
Explore fundamental structure of
matter
Investigate inter-relation of forces that
hold matter together
Highest energy density since BB
Mystery of dark matter
Mystery of antimatter
Study conditions of early universe
Test cosmological theory
T = 1019 K
t = 1x10-12 s
V = football
Cosmology
E = kT → T =
How
E = 14 TeV (2.2 µJ)
λ = hc/E = 1 x 10-19 m
Ultra high vacuum
Low temp: 1.6 K
LEP tunnel: 27 km
Superconducting magnets
600 M collisions/sec (1.3 kW)
Particle detectors
4 main detectors
• CMS
multi-purpose
•ATLAS multi-purpose
•ALICE quark-gluon plasma
•LHC-b antimatter decay
Particle detectors
Tracking device
measures momentum of charged
particle
Calorimeter
measures energy of particle by
absorption
Identification detector
measures velocity of particle by
Cherenkov radiation
• 9 accelerators
• recycling
• velocity increase?
K.E = 1/2mv2
m
m0
2
v
1
c2
II Particle physics (1930s)
• electron (1895)
• proton (1909)
• nuclear atom (1911)
Rutherford Backscattering
Periodic Table:
protons (1918)
• neutron (1932)
• what holds electrons in place?
• what holds nucleus together?
• what causes radioactivity?
Four forces of nature
Force of gravity
Holds cosmos together
Long range
Electromagnetic force
Holds atoms together
Strong nuclear force: holds
nucleus together
The atom
Weak nuclear force:
Beta decay
Strong force
strong force >> em
charge indep (p+, n)
short range
Heisenberg Uncertainty
massive particle
3 charge states
Yukawa pion (π)
Yukawa
Walton: accelerator physics
Cockcroft and Walton: linear accelerator
voltage multiplier: 0.5 MV →0.5 MeV
Protons used to split the nucleus (1932)
1H
1
+ 3Li6.9 → 2He4 + 2He4
Verified mass-energy (E= mc2)
Verified quantum tunnelling
Nobel prize (1956)
Cavendish lab, Cambridge
Ernest Walton (1903-95)
Born in Dungarvan
Early years
Limerick, Monagahan, Tyrone
Methodist College, Belfast
Trinity College Dublin (1922)
Cavendish Lab, Cambridge (1928)
Split the nucleus (1932)
Trinity College Dublin (1934)
Erasmus Smith Professor (1934-88)
New particles (1950s)
Cosmic rays
π+ → μ+ + ν
Particle accelerators
cyclotrons
synchrotrons
Particle Zoo (1950s, 1960s)
Over 100 particles
Quarks (1960s)
new periodic table
p+, n not fundamental
gauge symmetry
prediction of  SU3 → quarks
new fundamental particles
UP, DOWN, STRANGE
Stanford experiments 1969
Gell-Mann, Zweig
Quantum chromodynamics
scattering experiments
defining property = colour
SF = interquark force
asymptotic freedom
confinement
infra-red slavery
The energy required to produce a separation far exceeds
the pair production energy of a quark-antiquark pair,
Quark generations (1970s –1990s)
Six different quarks
(u,d,s,c,t,b)
Six leptons
(e, μ, τ, υe, υμ, υτ)
Gen I: all of ordinary matter
Gen II, III redundant
Meanwhile…
Gauge theory
Unified field theory of e and w forces
Salaam, Weinberg, Glashow
Single interaction above 100 GeV
Mediated by W,Z bosons
Predictions
• Weak neutral currents (1973)
• W and Z gauge bosons (CERN, 1983)
Rubbia and van der Meer
Nobel prize 1984
The Standard Model (1970s)
strong force = quark force (QCD)
em + weak force = electroweak
matter particles:fermions (spin ½)
(quarks and leptons)
force carriers:bosons (integer spin)
Prediction: W+-,Z0 boson
Detected: CERN, 1983
Standard Model: 1980s
• correct masses but Higgs boson outstanding
key particle: too heavy?
III LHC expectations (SM)
Higgs boson
Determines mass of other
particles
120-180 GeV
Set by mass of top quark, Z
boson
Search…surprise?
Main production mechanisms of the Higgs at the LHC
Ref: A. Djouadi,
hep-ph/0503172
Decay channels depend on the Higgs mass:
Ref: A. Djouadi, hep-ph/0503172
A summary plot:
Ref: hep-ph/0208209
Expectations II: supersymmetry
Unified field theory
Grand unified theory (GUT): 3 forces
Theory of everything (TOE): 4 forces
Supersymmetry
improves GUT (circumvents no-go theorems)
symmetry of fermions and bosons
gravitons: makes TOE possible
Phenomenology
Supersymmetric particles?
Not observed: broken symmetry
Expectations III: cosmology
?1. Finish SM (Higgs)
? 2. Beyond the SM (SUSY)
3. Missing antimatter?
LHCb
4. Nature of dark matter?
neutralinos?
High E = photo of early U
Particle cosmology
LHCb
• Where is antimatter?
• Asymmetry in M/AM decay
• CP violation
Tangential to ring
B-meson collection
Decay of b quark, antiquark
CP violation (UCD group)
Quantum loops
Summary
Higgs boson
Close chapter on SM
Supersymmetric particles
Open chapter on unification
Cosmology
Missing antimatter
Nature of Dark Matter
New particles/dimensions
Revise theory
Epilogue: CERN and Ireland
European Organization for Nuclear Research
World leader
20 member states
10 associate states
80 nations, 500 univ.
Ireland not a member
No particle physics in Ireland