s Why do we need them What do they look like Have we found them γ Quantum Electrodynamics predicts one massless spin1 gauge boson PHOTON g Quantum Chromodynamics predicts ID: 227968
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Slide1
Higgs boson(s)
Why do we need them?
What do they look like?
Have we found them?Slide2
γ
Quantum Electrodynamics
predicts one
massless
spin-1 gauge boson
PHOTONSlide3
g
Quantum
Chromodynamics
predicts
(32-1) = 8
massless
spin-1
gauge bosons
GLUONS
g
g
g
g
g
g
gSlide4
W
Z
Quantum Flavour Dynamics
predicts
(2
2-1) = 3 massless
spin-1
gauge bosons
?Slide5
W and Z boson are NOT massless
Mass of
W
bosons… 80 GeV Mass of Z bosons … 91 GeVWeigh more than a copper atomSlide6
Massive spin-1 particles
have
3
polarisationsHelicity = +1 or 0 or -1Slide7
Massless spin-1 particles have
only
2
polarisationsHorizontal or vertical polarised photonsHelicity = +1 or -1 onlyLongitudinal polarisation is lost!W and Z bosons need extra degree of polarisation as massiveSlide8
Giving mass to the W and Z
H
W or Z
W or Z
W and Z bosons
pick up
mass from
interaction
with new
scalar field
Pops out of vacuum & modifies propagator
New fieldSlide9
“Higgs” field
Field must have
non-zero vacuum value
everywhereUniverse filled with “relativistic ether” of this fieldCoupling to the field gives mass to W and ZSlide10
Symmetry breaking & the Higgs field
Require: underlying theory is
symmetric
Vacuum or ground state has broken symmetrySlide11
Magnetic material at high temperatures
Symmetric in directionSlide12
Magnetic material at low temperature
Symmetry broken – special directionSlide13
Broken symmetry for a complex fieldSlide14
Standard Model has complex doublet
4
degrees of freedom
3 end up as longitudinal polarisations of W and Z bosons1 left over – excitation of the field – Higgs BosonSlide15
In the Standard Model the SAME Higgs field
gives mass to the:
W boson
Z bosonall the quarks and leptonsSlide16
H
f
f
Higgs couplings to mass
HVVSlide17
Higgs boson production and
decay
BlackboardSlide18Slide19
Accelerator complex @ CERNSlide20
LIN
ear
ACcelerator Slide21Slide22
P
Reconstructing the debrisSlide23
Detectors…
Robotic assembly of precision silicon
tracker –
Denys Wilkinson BuildingSlide24
ATLAS
Segment of
detectorSlide25
H
Z + Z*
(
e+ + e-) + (e+ + e-) candidateSlide26Slide27
A collision producing 2 high-energy
photons
Higgs
+ ?Slide28
Higgs
2 photons
Bump at mass of new particleSlide29
CouplingsSlide30
What shape is the potential
Why is the mass of the Higgs boson not HUGE?
Does it couple to itself?
Many questions unanswered…
Are there more Higgs bosons?