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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… 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 MeV m =v = 105 MeV m =v =1750 MeV mu =uv = 4 MeV md =dv = 7 MeV ms =sv = 150 MeV mc =cv = 1500 MeV mb =bv = 5000 MeV mt =tv = 175,000 MeV etc. = e2/ħc = 1/137 w= 1/25 s = 1 MPL= 1/G1/2 = 1022 MeV v = 246,000 MeV =(10-9 MeV)4 MW =gw2v= 81,000 MeV mH2 = v2 = 125,000 MeV Vus =0.22 Vcb = 0.04 Vub= 0.002 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 By 1960s, people had found approximate symmetries in the interactions - would be exact symmetries if masses were zero Higgs mechanism – energetics to break symmetry V(H) 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 Finding the Higgs Large Hadron Collider (LHC) at CERN: 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