Modern Physics The Why, What, and How? of the Higgs Boson Sean Yeager University of Portland 10 April 2015
Outline Review of the Standard Model Review of Symmetries Symmetries in the Standard Model The Higgs Mechanism Electroweak Symmetry Breaking Searching for the Higgs The Compact Muon Solenoid The Future
The Standard Model 6 Quarks 6 Leptons 3 Forces 4 Mediators 1 Higgs...?
Symmetries and Conservation Noether (1918) Conservation laws correspond to symmetries Momentum : Translation Energy : Time Angular Momentum : Rotation We have particle conservation laws as well
Review of Laws Baryon number Quark number Lepton number Angular momentum Charge Flavor Energy (mass)
Practice Problems According to the SM, which of these reactions are possible? If not, say what law is violated. p+ + p - π + + π 0 n p + + ep+ + p + p + + p + + p + + p μ - e - + νe + ν μ e- + e + μ + + μ π0 γ + γ π0 p + + p -
Symmetries as Groups Explore symmetry in greater detail Consider equilateral triangle What operations that leave it unchanged? 3 rotations 3 reflections Transformations form a group Combination of members is also a member
Symmetries in Fields What can we vary without changing the Lagrangian? Gauge invariance Static electricity: V V+C Generalize to EM
Symmetries and Forces Yang and Mills (1954) Non-Abelian groups to understand strong force Can think of all 3 forces as arising from gauge symmetries Successful, but big problem Massless mediators
Aside into Solid State Physics Nambu and Goldstone (1960) Superconductors Look at chiral symmetry in fermions Symmetry breaking Field self interacts Produces massive particles
Higgs Mechanism Suggested by Anderson (1962) PRL Symmetry Breaking Articles (1964) Higgs Brout and Englert Guralnik, Hagen, and Kibble Combine a gauge field with another field that breaks the symmetry group Higgs bosons are excitations in field Gauge bosons interact with Higgs Bosons Gain mass based on strength of interaction
The Champagne Bottle Potential Ground state is nonzero Higher than surrounding area Symmetric central position is spontaneously broken by perturbation
Analogies Swimming Toddler vs. Shark Water : Higgs field Drag : coupling Political gathering Obama vs. Bush People : Higgs field Popularity : coupling
Electroweak Breaking Weinberg and Salam (1967) Assume a Higgs field Use it to break electroweak symmetry Predictions Neutral weak current Two charged weak mediators; mass of 82 ± 2 GeV One neutral weak mediator; mass 92 ± 2 GeV Observed at Gargamelle (CERN, 1973) Observed at Super Proton Synchotron (CERN, 1983) Masses 80.4 and 91.2 GeV Nobel Prize (1979)
Something is Missing They also predicted the Higgs Boson Didn't see it for 40 years Several more generations of accelerators Large Electron Positron Collider (CERN, 1989-2000) Superconducting Supercollider (Texas, canceled 1993) Would have been 20 TeV! Tevatron (Fermilab, 1989-2011) Relativistic Heavy Ion Collider (BNL, 2000-present) LHC (CERN 2009-present)
The Large Hadron Collider >10,000 scientists Proton-proton collisions From >100 countries Run 1 (2010-2012) 27 km circumference 175 m underground Spans two countries 7 TeV 8 TeV Run 2 (2015-?) 14 TeV
Compact Muon Solenoid
Interaction Point 2808 bunches of protons 1.15 x 1011 protons each Proton beams collide Cross every 25 ns Beam radius: 17μm 31.6 million collisions / sec
Silicon Tracker Charged particles Magnetic field 66 million sensors Measures momentum by looking at position Curvature and momentum inversely related Accurate to 10 μm
ECAL Lead tungstate PbWO4 Transparent Measures energy Electrons and photons cause scintillation >76,000 crystals
HCAL Layered heavy materials and plastic scintillators Brass and steel Measures energy of quark based particles Endcaps old artillery shells
Magnet Superconducting Provides field for tracker Niobium titanium 3.8 T; 18,160 A; 2.3 GJ 100,000 Earth's field About ½ tonne of TNT
Muon Detectors Drift tubes (barrel) Critical feature Cathode strip chambers (caps) Muons penetrate Gas and wire Not stopped by cals Muons ionize gas
The Higgs of July July 4 2012 ATLAS and CMS About 125 GeV 2 interaction channels 2 photon 4 lepton Both detectors saw excess in channels About 5 sigma ~125 GeV
So What's Next? Real world not much...for now? Validates Standard Model Scalar fields do exist in nature Cosmology Inflation? Fate of the universe?