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The Lonesome Higgs Click to edit Master title style Richard Kass • • • • • The Ohio State University Click to edit Master text styles Second level Outline ThirdIntroduction level to Higgs LHC and ATLAS Fourth level Finding the first Higgs particle Fifth level Finding the next Higgs particle Summary 1 3/26/2015 R. Kass/USC 1 What is a “Higgs” A person Click to edit Master title style • Click to edit Master text styles • Second levelPeter Higgs Professor Emeritus, University of Edinburgh • Thesis: Third“Some level PhD problems in the theory of molecular vibrations” Awards: Nobel Prize, Wolf Prize, Sakurai Prize, Dirac Medal,+++ • Fourth level A mechanism A way to eliminate • Fifth levelzero mass scalar particles and give mass to vector bosons in a theory with a spontaneously broken continuous symmetry. A field Its vacuum expectation value is responsible for giving mass to vector bosons, quarks, & charged leptons. A particle (aka “God particle”) A particle with mass ~125X that of a proton. 3/26/2015 R. Kass/USC 2 2 The Standard Model’s Building Blocks 1964 Click to(pre-) editStandard MasterModel title style • • • • • Click to edit Master text styles Second level Third level Fourth level Fifth level 3 3/26/2015 R. Kass/USC 3 A brief higgstory of HEP theory Click to edit Master title style 1950’s-early 1960’s: Search for a theory that has both massive & massless particles field theories (other than QED) give unphysical results field theory Vs S-matrix theory (looks like S-matrix will win….) Nambu-Goldstone theorem predicts massless scalar particles • Second level evidence for massless scalars But no experimental • Click to edit Master text styles 1964: • Third level 3 papers published in PRL on avoiding massless scalars • Fourth level • Fifth leveland the “Broken Symmetries “Broken Symmetry and the Mass of Gauge Vector Mesons, “ Englert, F. & Brout, R. PRL 13 (1964) 321-323 PRL 13 (1964) 508-509 Masses of Gauge Bosons ,” Higgs, Peter W. “Global Conservation Laws and Massless Particles,” G.S. Guralnik, C.R. Hagen, T.W.B. Kibble, PRL 13 (1964) 585-587 And let’s not forget: “Plasmons, Gauge Invariance, and Mass,” Anderson, Philip W. Phys. Rev. 130 (1963) 439-442 “Quasi-Particles and Gauge Invariance in the Theory of Superconductivity,” Yoichiro Nambu, Phys. Rev. 117, (1960) 648 4 3/26/2015 R. Kass/USC 4 What did these papers do? Higgs takes a theory from Goldstone & shows that with a suitable gauge transformation & a spontaneously broken symmetry the particle spectrum contains only a massive scalar & a massive vector. Click to edit Master title style • • • • • Click to edit Master text styles Second level Third level V(φ) Fourth level Fifth level -μ/λ +μ/λ φ V(φ)=-½μ2φ2+¼λ2φ4 V’(φ)=0 for φ=0, ± μ/λ V’’(μ/λ)>0 5 3/26/2015 R. Kass/USC 5 Higgs-steria?? Click edit Master title style Whatto is the reaction to these papers? • • • • • All the papers are ignored….. Click to edit Master text styles Yearly citations for Higgs, PRL 13 (1964) 508 Second level 1964-70: 14 citations! To date: > 3000 citations. Third level Other papers have same Fourth level citation history! Fifth level (including self-cites) 6 3/26/2015 R. Kass/USC 6 Higgs-steria?? Click to edit Master titlenotice? style What happened to make people take NOT: “A Model of Leptons,” Weinberg, PRL 19 (1967) 1264 (>9000 cites) AND NOT: “Regularization and Renormalization of Gauge Fields,” Gerard 't Hooft, M.J.G. Veltman Nucl.Phys. B44 (1972) 189-213 • Second level (> 3300 cites) • Click to edit Master text styles • Third level (Z) interactions were observed! Neutral Current A new interaction where a neutral spin 1 particle couples to a neutrino. • Fourth level • Fifth level No muon produced by interacting neutrino V F J Hasert et al. 1973a Phys. Lett. 46 121. F J Hasert et al. 1973b Phys. Lett. 46 138. 3/26/2015 R. Kass/USC 7 7 Mass Higgs-steria Click to edit Master title style >1000 citations • • • • • Nuclear Physics B106 (1976) 292 Click to edit Master text styles Second level Third level Fourth level Fifth level Unitarity puts an upper bound on the mass of the Higgs ≈ 1 TeV 1990 This book has its own facebook page*! 8 *https://www.facebook.com/pages/The-Higgs-Hunters-Guide/412484908831857 3/26/2015 R. Kass/USC 8 Standard Model Higgs Predictions The mass of the Higgs is not predicted in the standard Model. Click to edit Master title style it is a free parameter But how often it is produced in pp collisions Vs Higgs mass is! • Click to edit Master text styles • Second level • Third level Gluon Fusion Vector-Boson • Fourth level Fusion • Fifth level Higgs-strahlung Cross section for pp-> Higgs Vs MHiggs LHC at 8 TeV CM energy produces ~1000 Higgs/hr 9 3/26/2015 R. Kass/USC 9 Standard Model Higgs Predictions The mass of the Higgs is not predicted in the standard Model. But how often it decays into quarks, leptons, and vector bosons as a function of Higgs mass is! Click to edit Master title style • Click to edit Master text styles Higgs Branching fraction vs MHiggs • Second level MHiggs= 125 GeV • Third level • Fourth level • Fifth level hardest detection easiest 10 3/26/2015 R. Kass/USC 10 The Large Hadron Collider The LHC collides protons Center of Mass E=14 TeV ~7X Fermilab Very high luminosity ~100X Fermilab Click to edit Master title style LHC is located at CERN CERN is in France & Switzerland CERN is located near Geneva • • • • • 1232 superconducting dipole magnets B=~8T Click to edit Master text styles Second level Third level Fourth level Fifth level ATLAS site 9km main lab 5/29/2012 3/26/2015 SPS R. Kass/USC 11 The ATLAS Experiment Click to edit Master title style • Click to edit Master text styles • Second level • Third level outside good momentum, energy, & vertex • Fourth level detector resolution Identify muons, electrons, photons • Fifth level Reconstruct b-jets, taus flexible triggers Hermetic detector: can look for missing energy signatures inside detector Optimized to look for Higgs particles & BSM physics processes12 3/26/2015 R. Kass/USC 12 pp-> Z->μ+μ-+ other stuff Click to edit Master title style • • • • • Click to edit Master text styles Second level Third level Fourth level Fifth level Many collisions within 50 ns. 13 3/26/2015 R. Kass/USC 13 Discovering the Standard Model at the LHC Before you can discover new physics must discover the old physics. Standard Model has many predictions for cross sections. Click to edit Master title style Excellent test of how well the ATLAS detector works. Click to edit Master text styles Second level Third level Fourth level Fifth level cross section • • • • • Measurements & predictions agree over ~ 12 orders of magnitude 14 3/26/2015 R. Kass/USC 14 Higgs->γγ Candidate To “find” a particle calculate the invariant mass of its decay products Click to edit Master title style • Click to edit Master text styles 2 energetic • Second level gammas • Third level • Fourth level • Fifth level Invariant Mass of two particles: m2=(E1+E2)2-(P1+P2)2 For photons: m2=Eγ1Eγ2(1-cosθ) 3/26/2015 R. Kass/USC 15 15 Higgs Particle Discovery Modes Click to edit Master title style • • • • • H->ZZ*->4 leptons H->γγ (e+e-e+e- /μ+μ-μ+μ- /e+e-μ+μ-) Click to edit Master text styles Second level Third level Fourth level Fifth level Also observed: H->WW*, H->bb, and H->τ+τHiggs decay into dibosons, quarks, and leptons All decay channels consistent with mass=125 GeV 3/26/2015 R. Kass/USC 16 16 The standard model is “complete” we done? title style Click to editAreMaster • • • • • Click to edit Master text styles Second level Third level Fourth level Fifth level 17 3/26/2015 R. Kass/USC 17 Beyond the standard model Many important issues remain! The Standard model is incomplete: Click to edit Master title style Cannot predict the mass of the Higgs or how many Higgs particles. The minimum is one, but there can be more! Does not contain dark matter or dark energy. Magnitude of CP violation for baryon asymmetry (CKM CPV too small) • Second level No gravity Neutrino mass ? • Click to edit Master text styles • Third level Why generations • three Fourth levelof quarks and leptons & >19 parameters? The “Hierarchy” problem: Why is the Higgs • Fifth levelso light compared to the Planck scale: 102 Vs 1019 GeV Technical problems: Quantum corrections to the Higgs mass are larger than 125 GeV. Corrections must cancel at an amazing level: implies fine tuning to 1 part in ~1030 Muv~Mplanck~1019 GeV 18 3/26/2015 R. Kass/USC 18 Going Beyond the Standard Model Supersymmetry is a popular BSM with an extended Higgs sector Click to edit Master title style SUSY is a theory with symmetry between fermions & bosons. For every SM particle there is a SUSY particle with spin that differs by ½. Eliminates hierarchy problem SUSY compatible with string theory & SM • Click to edit Master text styles Natural extension to grand unified theories • Second level Lightest SUSY particle may be stable and might be dark matter SUSY may contain a new conserved quantum number, R • ThirdB=baryon level#, L=lepton #, S=spin, R=1 for SM, -1 for SUSY particles R=(-1) If R is conserved, SUSY particles must be produced in pairs. • Fourth level BUT SUSY has ~ 100 free parameters! • Fifth level Many possible models to consider, masses of SUSY particles unspecified. 3(B-L)+2S Minimal Supersymmetric Model (MSSM) 5 Higgs particles: 3 neutral scalars (2 CP even, 1 CP odd), 2 charged scalars, H± Next-to-Minimal Supersymmetric Model (NMSSM) 7 Higgs particles 5 neutral scalars (3 CP even, 2 CP odd), 2 charged scalars, H± 3/26/2015 R. Kass/USC 19 19 Many BSMs with Higgs Particles Click to edit Master title style Minimal Composite Higgs Model (MCHM) (1 Higgs) Higgs boson = composite (pseudo-Nambu-Goldstone boson) strong interaction to the rescue => no hierarchy problem • Click to edit Master text styles (2 Higgs) Single additional electroweak singlet simplest extension, • Second level two CP-even Higgs bosons Two Higgs Doublet Models (2HDM) (5 Higgs) • Third level additional doublet h0, H0 (CP-even), A0 (CP-odd), H± => fixeslevel hierarchy problem • Fourth 4 types based on coupling structure (Type II = MSSM) • Fifth level SUSY (NMSSM) Next-to-Minimal (7 Higgs) MSSM + complex singlet(S): H1, H2, H3, A1, A2, H± =>generates MSSM μ-term through S spontaneous symmetry breaking Higgs Triplet Model h0, H0 (CP-even), A0 (CP-odd), H±, H±± => generates neutrino masses/mixings 3/26/2015 (7 Higgs) 20 R. Kass/USC 20 Which Higgs have we found? Is the 125 GeV Higgs consistent with the standard model? Detailed studies show quantum numbers are consistent with JPC=0++ Click to edit Master title style scalar Vs pseudoscalar • Click to edit Master text styles Can rule out spin 1, 2, mixtures, etc. • Second level • Third level Couplings & branching fractions to fermions & vector bosons are SM. • Fourth level Higgs Coupling Vs mass • Fifth level All production & decay measurements are consistent with SM! 3/26/2015 R. Kass/USC 21 21 Direct Higgs Searches Search Higgs/scalar Clickfor toadditional edit Master title particles… style Generic searches looking for H->γγ, ZZ(*), WW(*), bb, tt, etc for more massive versions of H(125) •Look Click to edit± Master text styles ± Charged Scalars H ->ZW , cs, τν, etc by SUSY & other BSMs •predicted Second level Scalars that decay into other scalars • Third level can happen if m >2*(125 GeV) Scalars that level violate lepton number (e.g. H-> τμ) • Fourth possible in SUSY and Randall Sundrum models • Fifth level Scalars that decay into undetectable particles Since Higgs couples to mass decays into neutrinos highly suppressed Unaccounted for “missing” energy in the detector 22 3/26/2015 R. Kass/USC 22 Higgs Decay to γγ/ZZ*/WW* Click to edit Master title style H->γγ No evidence up to ~600 GeV • Click to edit Master text styles • Second level • Third level (*) → 4leptons H→ ZZ • Fourth level No evidence up to ~900 GeV ATLAS-CONF-2013-013 • Fifth level ATLAS: arXiv:1407.6583 [hep-ex] CMS-PAG-HIG-14-006 CMS: Phys. Rev D 89. 092007 H->WW(*) No evidence up to ~1000 GeV ATLAS-CONF-2013-067 CMS-HIG-13-023 3/26/2015 R. Kass/USC 23 23 Search for charged Higgs, H± Search for Charged H± →W± Z Click to edit Master title style • • • • • Click to edit Master text styles Second level Third level Fourth level Fifth level No signal, set model dependent limits Many other searches for more Higgs particles: h0, H± & H±± No signals, set limits that depend on mass and x-section 24 3/26/2015 R. Kass/USC 24 What is next? The LHC is preparing to operate at 13/14 TeV CM energy Higher CM energy = 1.75X more H(125)’s Click to edit Master title style Click to edit Master text styles Second level Third level Fourth level Higgs production modes Fifth level Higgs cross section • • • • • LHC luminosity to increase 2X + more days taking data >10X increase in H(125) sample in ~ 3 years LHC has a plan to take data that goes until 2035! Will increase sensitivity to finding additional Higgses by >100X 25 3/26/2015 R. Kass/USC Summary Click to edit Master title style We have found the scalar particle predicted by Higgs. Its mass is 125 GeV Englert & Higgs --> • Click to edit Master text styles All particles of the standard model are now accounted for. • Second level We need “new” physics to explain why the SM works so well. We•need “new” physics to explain the physics not in the SM. Third level The most popular NP models contain additional Higgs Bosons. • Fourth level Despite intense efforts by ATLAS and CMS there is no evidence for any additional scalar particles with m> 100 GeV and < ~ 1 TeV • Fifth level More results https://twiki.cern.ch/twiki/bin/view/CMSPublic/PhysicsResultsHIG https://twiki.cern.ch/twiki/bin/view/AtlasPublic/HiggsPublicResults The next chapter in the hunt for more Higgs bosons begins in a few months when ATLAS & CMS start collecting 13 TeV CM energy data. How much longer will the Higgs be lonesome? 26 3/26/2015 R. Kass/USC 26 Extra Slides Click to edit Master title style • • • • • Click to edit Master text styles Second level Third level Fourth level Fifth level 3/26/2015 27 R. Kass/USC 27