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 particlesFrom Walton to the Standard Model
III. LHC Expectations
The Higgs boson
Beyond the Standard Model
Particle cosmology
The Large Hadron Collider (CERN)
No black holes
High-energy proton beams
Head-on collision
Huge energy density
Create short-lived particles
E = mc2
Detection and measurement
Why
Explore fundamental structure of matter
Investigate inter-relation of forces that hold matter together
T = 1019 K
t = 1x10-12 s
V = football
Study conditions of early universe Test cosmological theory
Mystery of dark matter Mystery of antimatter
Highest energy density since BB
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 devicemeasures momentum of charged particle
Calorimeter measures energy of particle by
absorption
Identification detector measures velocity of particle by Cherenkov radiation
2
2
0
1c
v
mm
• recycling
• 9 accelerators
• velocity increase?
K.E = 1/2mv2
II Particle physics (1930s)
• electron (1895)
• proton (1909)
• nuclear atom (1911) Rutherford Backscattering
• what holds electrons in place? • what holds nucleus together? • what causes radioactivity?
Periodic Table: protons (1918)
• neutron (1932)
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
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)
Nobel prize (1956)
1H1 + 3Li6.9 → 2He4 + 2He4
Verified mass-energy (E= mc2)Verified quantum tunnelling
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 Particle accelerators
cyclotronssynchrotronsπ+ → μ+ + ν
Particle Zoo (1950s, 1960s)
Over 100 particles
Quarks (1960s)
new periodic tablep+, n not fundamental gauge symmetry
prediction of -
SU3 → quarksnew fundamental particlesUP, DOWN, STRANGE
Gell-Mann, ZweigStanford experiments 1969
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 MeerNobel 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
Ref: hep-ph/0208209
A summary plot:
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
Tangential to ringB-meson collectionDecay of b quark, antiquarkCP violation (UCD group)
• Where is antimatter?• Asymmetry in M/AM decay• CP violation
Quantum loops
SummaryHiggs bosonClose chapter on SM
Supersymmetric particlesOpen chapter on unification
CosmologyMissing antimatterNature of Dark Matter
New particles/dimensionsRevise theory
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