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