# 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.

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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 Donoghue July 10, 2012

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 reductionists Universe: The Standard Model = with gauge group SU(3)xSU(2) L xU(1) and 3 generations

Basic features in words: 1)Fundamental particles: World Atoms Nuclei 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 m e = e v = 0.511 MeV m = v = 105 MeV m = v =1750 MeV m u = u v = 4 MeV m d = d v = 7 MeV m s = s v = 150 MeV m c = c v = 1500 MeV m b = b v = 5000 MeV m t = t v = 175,000 MeV m e = e v = 0.511 MeV m = v = 105 MeV m = v =1750 MeV m u = u v = 4 MeV m d = d v = 7 MeV m s = s v = 150 MeV m c = c v = 1500 MeV m b = b v = 5000 MeV m t = t v = 175,000 MeV v = 246,000 MeV L=(10 -9 MeV) 4 M W =g w 2 v= 81,000 MeV m H 2 = v 2 = 125,000 MeV V us =0.22 V cb = 0.04 V ub = 0.002 etc. = e 2 /ħc = 1/137 w = 1/25 s = 1 M PL = 1/G 1/2 = 10 22 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( H ) 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

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