the higgs boson what it is: 1) barroom explanation 2) more, with some pictures 3) yet more, with...
TRANSCRIPT
The Higgs boson
What it is: 1) barroom explanation 2) more, with some pictures 3) yet more, with some formulas
Plus pictures related to the discovery
John DonoghueJuly 10, 2012
1) A Higgs boson walk into a bar…
1) A Higgs boson walk into a bar…
Basic points:
-In fundamental theory without Higgs, all particles travel at speed of light -Higgs is like “molasses” filling space – slows them down-gives them mass
Significance – completes our fundamental theory (SM) - without Higgs – no atoms, no stars …..
1) A Higgs boson walk into a bar…
And the atmosphere gets heavy…
He walks out and everyone falls apart…
“What are we trying to explain?
2MASS =UMass +
The reductionist’s Universe: The Standard Model
=
with gauge group SU(3)xSU(2)LxU(1) and 3 generations
Basic features in words:
1) Fundamental particles: World AtomsNuclei Quarks and Leptons
2) Fundamental forces/fields: Strong – holds nuclei together Electroweak – Electricity, Magnetism + atomic forces, light,.... Gravity – structure of universe at large scales
Relevant fact: 26 parameters
me =ev = 0.511 MeVm =v = 105 MeVm =v =1750 MeVmu =uv = 4 MeVmd =dv = 7 MeVms =sv = 150 MeVmc =cv = 1500 MeVmb =bv = 5000 MeVmt =tv = 175,000 MeV
me =ev = 0.511 MeVm =v = 105 MeVm =v =1750 MeVmu =uv = 4 MeVmd =dv = 7 MeVms =sv = 150 MeVmc =cv = 1500 MeVmb =bv = 5000 MeVmt =tv = 175,000 MeV
v = 246,000 MeV=(10-9 MeV)4
MW =gw2v= 81,000 MeV
mH2 = v2 = 125,000 MeV
Vus =0.22Vcb = 0.04Vub= 0.002etc.
= e2/ħc = 1/137w= 1/25s = 1 MPL= 1/G1/2 = 1022 MeV
Also tied to “symmetry breaking”
Symmetry in the fundamental interactions:
Early on, evidence of hidden symmetry found: - electron related to neutrino - up quark and down quark related - W, Z related - but masses break the symmetry
There is mathematics of “group theory” at work - SM = SU(3) x SU(2) x U(1)
But symmetry seems broken or hidden
Little advertised fact: theory start with four Higgs bosons - all equivalent due to symmetry
The Higgs “vacuum expectation value”
Standard Model relies on symmetry breaking of Higgs scalar
V()
By 1960s, people had found approximate symmetries in the interactions - would be exact symmetries if masses were zero
Higgs mechanism – energetics to break symmetry
Logic of symmetry breaking and mass generation
Basic theory has symmetry and massless particles
Higgs sector shares these properties, but
Energetics favor solution with a constant field everywhere
This then breaks symmetry
In this background field, particles have mass
Including Higgs itself
Now some equations:
Electricity and magnetism and photons:
Particle with mass:
Particle with Higgs
The Higgs mechanism:
Minimize energy
Source term now becomes mass term
Excitation around constant field is Higgs particle
Large Hadron Collider (LHC) at CERN:
Finding the Higgs
UMass participates on the ATLAS experiment
How one sees a Higgs boson:
Another decay process:
Discovery significance
Is it really the SM Higgs?
The Nobel dilemma:
My bet: Higgs, Englert and Brout