Transcript The Big Bang, the LHC and the Higgs Boson Dr Cormac O’ Raifeartaigh (WIT)

The Big Bang, the LHC and the Higgs Boson
Dr Cormac O’ Raifeartaigh (WIT)
Overview
I. LHC
What, How and Why
II. Particle physics
The Standard Model
III. LHC Expectations
The Higgs boson and beyond
Big Bang cosmology
The Large Hadron Collider
High-energy proton beams
Opposite directions
Huge energy of collision
Create short-lived particles
E = mc2
Detection and measurement
No black holes
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 universe
Highest energy since BB
1019
T=
K
t = 1x10-12 s
V = football
Mystery of dark matter
Mystery of antimatter
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 device
measures 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
Periodic Table:
protons (1918)
• neutron (1932)
• what holds nucleus together?
• what holds electrons in place?
• 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
SF >> em
charge indep
protons, neutrons
short range
HUP
massive particle
Yukawa pion
3 charge states
New particles (1950s)
Cosmic rays
π+ → μ+ + ν
Particle accelerators
cyclotron
Particle Zoo (1960s)
Over 100 particles
Quarks (1960s)
new periodic table
p+,n not fundamental
symmetry arguments
(SU3 gauge symmetry)
SU3 → quarks
new fundamental particles
UP and DOWN
prediction 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 Mass
The strong nuclear force cannot explain the mass of the electron
though…
Or very heavy quarks
top mass = 175 proton mass
The Higgs Boson
We suspect the vacuum is full of another sort of matter that is
responsible – the higgs…. a new sort of matter – a scalar?
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
Higgs decay channels
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.
Decay channels depend on the Higgs mass:
Ref: A. Djouadi, hep-ph/0503172
A summary plot:
Ref: hep-ph/0208209
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
1. Unification of forces: SUSY
2. SUSY = dark matter?
double whammy
3. Matter/antimatter
asymmetry?
LHCb
√ 2. Unification of forces
3. Nature of dark matter?
neutralinos?
4. Missing antimatter?
LHCb
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 new chapter: TOE
Cosmology
Nature of Dark Matter
Missing antimatter
Unexpected particles?
New avenues
http://coraifeartaigh.wordpress.com
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