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