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Jim Olsen Princeton University Princeton Plasma Physics Laboratory Colloquium September 26, 2012 Is it the Higgs Boson? Slide 2 Many Princeton undergraduate students have worked on the CMS experiment over the years Pierre Pirou Slide 3 Slide 4 Slide 5 Searching for the Higgs boson took: Fifty years, thousands of people, and billions of dollars. Why all the fuss? Slide 6 CMS and ATLAS submitted their papers to Physics Letters on July 31. As of today, each paper has been cited 128 times: Impact Dark Matter Supersymmetry Muon g-2 Vacuum stability Exotic BSM Physics Neutrino Physics The precise nature of this new particle touches on all of these topics, and more. The LHC (and future iterations) may not be sufficient to answer all questions. Slide 7 Outline Invention and early Higgs hunting Discovery of a new boson at the LHC Is it the Higgs boson? Slide 8 One field to rule them all Standard Model Matter: quarks and leptons Symmetries: U(1) Y, SU(2) L, SU(3) C Local gauge invariance: gauge bosons (force carriers) Higgs field: spontaneous symmetry breaking and the Higgs boson Slide 9 Whats the problem? Applying local U(1) invariance,, to the Dirac Lagrangian: Free fermionsGauge interactionFree gauge bosons The term is not gauge invariant need massless gauge bosons U(1) EM : photon is the gauge boson electromagnetic interactions SU(2) L : W +, W -, Z 0 are the gauge bosons weak interactions SU(3) C : gluons (8 of them) are the gauge bosons strong interactions Works for the EM and strong interactions, but W and Z bosons are massive (~100 GeV). Need a mechanism to give mass to gauge bosons. Slide 10 The Higgs* Mechanism * actually, the Nambu-Goldstone-Anderson-Englert-Brout-Higgs-Guralnik-Hagen-Kibble mechanism vev Expand around minimum: Gauge invariance: Gauge boson mass! Mass of a real scalar particle: Higgs boson! Slide 11 Properties of the SM Higgs boson Mass: Because is not predicted, the Higgs boson mass is a free parameter Interaction: couples to particles according to their mass Slide 12 Is this the only possibility? NO! Additional Higgs fields i Composite Higgs: top-quark condensate Technicolor: new gauge interactions Extra dimensions Critical to determine if the new particle is the SM Higgs boson Slide 13 Higgs Hunting: 1975 2010 Slide 14 Higgs Phenomenology: 1975 Ellis, Gaillard, and Nanopoulos, Nucl. Phys. B106, 292 125 GeV Slide 15 Bounds on the SM Higgs Mass: 1976 and A. Linde, JETP Lett. 23 (1976) 64 Slide 16 Discovery of the Zeta(8.3) with the Crystal Ball detector + X Was not confirmed in later runs. 1984 Slide 17 The Role of the Top Quark The top quark was discovered at Fermilab in 1995 with a mass near 173 GeV, clearly indicating its strong coupling to the Higgs field This result ushered in the modern era of Higgs searches at LEP and FNAL Cabibbo, Maiani, Parisi, Petronzio, Nucl. Phys. B158 (1979) 295 Slide 18 Searching at LEP Operating at CERN from 1989 - 2000 Line shape of the Z 0 boson (number of light s) Search for the Higgs boson Slide 19 LEP Legacy Search strategy: Produced via Higgs-strahlung Slide 20 Operating at FNAL from 1985 - 2011 Discovery of the top quark Search for the Higgs boson Slide 21 At the dawn of the LHC era Slide 22 Discovery of a new boson at the LHC Slide 23 Large Hadron Collider proton-proton collider inside the 27km LEP tunnel: Construction: 1998-2008 Operation: 2009 - 1232 superconducting dipole magnets with B > 8 Tesla Worlds largest cryogenic plant 2011: 5fb -1 @ 7 TeV 2012: >10fb -1 @ 8 TeV Slide 24 ATLAS and CMS Humans ~3000 scientist, engineers, and students working on each experiment Giant multipurpose particle detectors designed to find or exclude the Higgs boson and signs of physics beyond the SM Slide 25 Standard Model @ CMS Top Cross Sections Slide 26 Higgs Boson Production at the LHC Gluon FusionVector-Boson Fusion Higgs-strahlung Slide 27 What does a Higgs boson look like? @Low mass Narrow! Observed width dominated by detector resolution @High mass Higgs becomes a broad resonance dominated by natural width Theory input is critical Det. Res. = 1-2% (, ZZ) Slide 28 How does it Decay (m H = 125 GeV) ? Branching Fractions (%) Cross sections are large Fermion decays (bb+ ) are accessible Natural width is negligible Only region in m H where Slide 29 LHC Searches CMS Discovery Potential Sensitivity Detector Resolution WW bb 1% 10% 20% Slide 30 Compact Muon Solenoid (CMS) Slide 31 Searching for H Slide 32 ~10 cm Slide 33 Mass scale and resolution Calibrated at the Z pole Slide 34 Diphoton invariant mass ATLASCMS > 4 Slide 35 ProbabilityInterpretation Evidence Compelling Evidence Observation Slide 36 Searching for H ZZ 4 leptons > 3 Slide 37 Searching for H WW 2l2 > 2 Slide 38 Adding*, ZZ, and WW (4+3+2=5) *ASSUMING it is the SM Higgs! > 5 Slide 39 Do CMS and ATLAS agree on the mass? Slide 40 As a layman, I think we have it. But as a scientist, I have to say, `What do we have? R. Heuer AP photo Slide 41 N. Arkani-Hamed (SavasFest 2012) Slide 42 Impact of a 125 GeV Higgs boson Giudice and Strumia, Nucl. Phys. B858 (2012) 63 Slide 43 Impact of a 125 GeV Higgs boson Vacuum Stability The vacuum is unstable but sufficiently long-lived, compared to the age of the universe. G. Isidori (Higgs Hunting 2012) Slide 44 Is it the (SM) Higgs boson? Slide 45 Where do we stand? Are the relative couplings consistent with prediction? Is it spin 0 or 2? Is it a scalar or a pseudoscalar? Does it couple to fermions? Does it decay to exotic final states? Observation in CMS and ATLAS of a new boson with a mass of roughly 125 GeV decaying to vector bosons It is certainly looking and walking like the SM Higgs boson. Does it also quack like the SM Higgs boson? Some questions: Slide 46 Does it couple to fermions? In the context of the SM Higgs boson phenomenology, we already have strong indirect evidence for a coupling to the top quark via the loop in the dominant production mechanism. Slide 47 Final results from the Tevatron 2.5 (Global) 2.9 (bb) Is the Tevatron seeing H bb? Slide 48 Search for and bb at CMS What to watch for in November: Is the SM Higgs boson excluded in ? Is there growing or shrinking evidence in bb? CMS has better sensitivity for H bb than any other experiment Slide 49 Pattern of couplings Overall, consistent with the SM expectation, but far from excluding other possibilities (and hint of something in ) Slide 50 Is g the same for W and Z? Slide 51 Global consistency? Slide 52 Does it have the right spin/parity? So far, not enough data to determine spin or parity Difficult to separate 0 and 2, easier to check + vs. - With the data expected by end of the year, maybe Slide 53 Does it decay to exotic final states? Branching Fractions (%) Until the bb channel is seen, constraints on the full width will be weak. Slide 54 Is it the SM Higgs boson? Are the relative couplings consistent with prediction? Is it a spin 0 scalar? Does it couple to fermions? Does it decay to exotic final states? Maybe! Would I buy SM Higgs boson stock? Probably! Slide 55 7 + 8 TeV: ~20fb -1