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Richard Kass The Ohio State University

The Lonesome Higgs. Richard Kass The Ohio State University. Outline Introduction to Higgs LHC and ATLAS Finding the first Higgs particle Finding the next Higgs particle Summary. What is a “Higgs”. A person. Peter Higgs Professor Emeritus, University of Edinburgh

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Richard Kass The Ohio State University

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  1. The Lonesome Higgs Richard Kass The Ohio State University Outline Introduction to Higgs LHC and ATLAS Finding the first Higgs particle Finding the next Higgs particle Summary R. Kass/USC

  2. What is a “Higgs” A person Peter Higgs Professor Emeritus, University of Edinburgh PhD Thesis: “Some problems in the theory of molecular vibrations” Awards: Nobel Prize, Wolf Prize, Sakurai Prize, Dirac Medal,+++ A mechanism A way to eliminate zero 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. R. Kass/USC

  3. The Standard Model’s Building Blocks 1964 (pre-) Standard Model R. Kass/USC

  4. A brief higgstory of HEP theory 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 But no experimental evidence for massless scalars 1964: 3 papers published in PRL on avoiding massless scalars “Broken Symmetry and the Mass of Gauge Vector Mesons, “ Englert, F. & Brout, R. PRL 13 (1964) 321-323 “Broken Symmetries and the Masses of Gauge Bosons ,” Higgs, Peter W. PRL 13 (1964) 508-509 “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 R. Kass/USC

  5. 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. V(φ)=-½μ2φ2+¼λ2φ4 V’(φ)=0 for φ=0, ± μ/λ V’’(μ/λ)>0 V(φ) φ +μ/λ -μ/λ R. Kass/USC

  6. Higgs-steria?? What is the reaction to these papers? All the papers are ignored….. Yearly citations for Higgs, PRL 13 (1964) 508 1964-70: 14 citations! (including self-cites) To date: > 3000 citations. Other papers have same citation history! R. Kass/USC

  7. Higgs-steria?? What happened to make people take notice? 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 (> 3300 cites) Neutral Current (Z) interactions were observed! A new interaction where a neutral spin 1 particle couples to a neutrino. 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. R. Kass/USC

  8. Mass Higgs-steria >1000 citations Nuclear Physics B106 (1976) 292 1990 Unitarity puts an upper bound on the mass of the Higgs ≈ 1 TeV This book has its own facebook page*! R. Kass/USC *https://www.facebook.com/pages/The-Higgs-Hunters-Guide/412484908831857

  9. Standard Model Higgs Predictions The mass of the Higgs is not predicted in the standard Model. it is a free parameter But how often it is produced in pp collisions Vs Higgs mass is! Vector-Boson Fusion Gluon Fusion Higgs-strahlung Cross section for pp-> Higgs Vs MHiggs LHC at 8 TeV CM energy produces ~1000 Higgs/hr R. Kass/USC

  10. 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! Higgs Branching fraction vs MHiggs MHiggs= 125 GeV easiest hardest detection R. Kass/USC

  11. The Large Hadron Collider The LHC collides protons Center of Mass E=14 TeV ~7X Fermilab Very high luminosity ~100X Fermilab LHC is located at CERN CERN is in France & Switzerland CERN is located near Geneva 1232 superconducting dipole magnets B=~8T ATLAS site 9km main lab 5/29/2012 R. Kass/USC SPS

  12. The ATLAS Experiment outside detector good momentum, energy, & vertex resolution Identify muons, electrons, photons Reconstruct b-jets, taus flexible triggers Hermetic detector: can look for missing energy signatures inside detector R. Kass/USC Optimized to look for Higgs particles & BSM physics processes

  13. pp-> Z->μ+μ-+ other stuff Many collisions within 50 ns. R. Kass/USC

  14. 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. Excellent test of how well the ATLAS detector works. cross section Measurements & predictions agree over ~ 12 orders of magnitude R. Kass/USC

  15. Higgs->γγ Candidate To “find” a particle calculate the invariant mass of its decay products 2 energetic gammas Invariant Mass of two particles: m2=(E1+E2)2-(P1+P2)2 For photons: m2=Eγ1Eγ2(1-cosθ) R. Kass/USC

  16. Higgs Particle Discovery Modes H->ZZ*->4 leptons (e+e-e+e- /μ+μ-μ+μ- /e+e-μ+μ-) H->γγ Also observed: H->WW*, H->bb, and H->τ+τ- Higgs decay into dibosons, quarks, and leptons All decay channels consistent with mass=125 GeV R. Kass/USC

  17. The standard model is “complete” Are we done? R. Kass/USC

  18. Beyond the standard model Many important issues remain! The Standard model is incomplete: 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) No gravity Neutrino mass ? Technical problems: Why three generations of quarks and leptons & >19 parameters? The “Hierarchy” problem: Why is the Higgs so light compared to the Planck scale: 102 Vs 1019 GeV 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 R. Kass/USC

  19. Going Beyond the Standard Model Supersymmetry is a popular BSM with an extended Higgs sector 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 Natural extension to grand unified theories Lightest SUSY particle may be stable and might be dark matter SUSY may contain a new conserved quantum number, R R=(-1)3(B-L)+2S B=baryon #, L=lepton #, S=spin, R=1 for SM, -1 for SUSY particles If R is conserved, SUSY particles must be produced in pairs. BUT SUSY has ~ 100 free parameters! Many possible models to consider, masses of SUSY particles unspecified. 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± R. Kass/USC

  20. Many BSMs with Higgs Particles Minimal Composite Higgs Model (MCHM) (1 Higgs) Higgs boson = composite (pseudo-Nambu-Goldstone boson) strong interaction to the rescue => no hierarchy problem Single additional electroweak singlet (2 Higgs) simplest extension, two CP-even Higgs bosons Two Higgs Doublet Models (2HDM) (5 Higgs) additional doublet h0, H0 (CP-even), A0 (CP-odd), H± => fixes hierarchy problem 4 types based on coupling structure (Type II = MSSM) Next-to-Minimal SUSY (NMSSM) (7 Higgs) MSSM + complex singlet(S): H1, H2, H3, A1, A2, H± =>generates MSSM μ-term through S spontaneous symmetry breaking Higgs Triplet Model (7 Higgs) h0, H0 (CP-even), A0 (CP-odd), H±, H±± => generates neutrino masses/mixings R. Kass/USC

  21. 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++ scalar Vs pseudoscalar Can rule out spin 1, 2, mixtures, etc. Couplings & branching fractions to fermions & vector bosons are SM. Higgs Coupling Vs mass R. Kass/USC All production & decay measurements are consistent with SM!

  22. Direct Higgs Searches Search for additional Higgs/scalar particles… Generic searches looking for H->γγ, ZZ(*), WW(*), bb, tt, etc Look for more massive versions of H(125) Charged Scalars H±->ZW±, cs, τν, etc predicted by SUSY & other BSMs Scalars that decay into other scalars can happen if m >2*(125 GeV) Scalars that violate lepton number (e.g. H-> τμ) possible in SUSY and Randall Sundrum models Scalars that decay into undetectable particles Since Higgs couples to mass decays into neutrinos highly suppressed Unaccounted for“missing” energy in the detector R. Kass/USC

  23. Higgs Decay to γγ/ZZ*/WW* H->γγ No evidence up to ~600 GeV ATLAS: arXiv:1407.6583 [hep-ex] CMS-PAG-HIG-14-006 H → ZZ(*) → 4leptons No evidence up to ~900 GeV ATLAS-CONF-2013-013 CMS: Phys. Rev D 89. 092007 H->WW(*) No evidence up to ~1000 GeV ATLAS-CONF-2013-067 CMS-HIG-13-023 R. Kass/USC

  24. Search for charged Higgs, H± Many other searches for more Higgs particles: h0, H± & H±± Search for Charged H±→W± Z No signal, set model dependent limits No signals, set limits that depend on mass and x-section R. Kass/USC

  25. What is next? The LHC is preparing to operate at 13/14 TeV CM energy Higher CM energy = 1.75X more H(125)’s Higgs cross section Higgs production modes 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 R. Kass/USC

  26. Summary We have found the scalar particle predicted by Higgs. Its mass is 125 GeV --> Englert & Higgs All particles of the standard model are now accounted for. We need “new” physics to explain why the SM works so well. We need “new” physics to explain the physics not in the SM. The most popular NP models contain additional Higgs Bosons. More results https://twiki.cern.ch/twiki/bin/view/CMSPublic/PhysicsResultsHIG https://twiki.cern.ch/twiki/bin/view/AtlasPublic/HiggsPublicResults Despite intense efforts by ATLAS and CMS there is no evidence for any additional scalar particles with m> 100 GeV and < ~ 1 TeV 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? R. Kass/USC

  27. Extra Slides R. Kass/USC

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