The Big Bang, the LHC and the Higgs Boson

Dr Cormac O’ Raifeartaigh (WIT)

Overview

I. LHC

What, How and Why

II. Particle physicsThe Standard Model

III. LHC Expectations

The Higgs boson and beyond

Big Bang cosmology

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

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

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

Cosmology

E = kT → T =

Particle cosmology

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

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)

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

SF >> em

charge indep

protons, neutrons

short range

HUP

massive particle

Yukawa pion

3 charge states

New particles (1950s)

Cosmic rays Particle accelerators

cyclotronπ + → μ + + ν

Particle Zoo (1960s)

Over 100 particles

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

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,

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

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

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

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

Standard Model : 1980s

• Experimental success 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

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

Decay channels depend on the Higgs mass:

Ref: A. Djouadi, hep-ph/0503172

Ref: hep-ph/0208209

A summary plot:

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

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

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 new chapter: TOE

CosmologyNature of Dark MatterMissing antimatter

Unexpected particles?New avenues

http://coraifeartaigh.wordpress.com

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