Higgs, more Higgs, less Higgs, or Higgsless? John Ellis King’s College, London (& CERN) The ‘Standard Model’ of Particle Physics Proposed byAbdus Salam, Glashow and Weinberg Tested by experiments at CERN & elsewhere Perfect agreement between theory and experiments in all laboratories Open Questions beyond the Standard Model • What is the origin of particle masses? LHC due to a Higgs boson? • Why so many flavours of matter particles?LHC • What is the dark matter in the Universe? LHC • Unification of fundamental forces? LHC • Quantum theory of gravity? LHC Why do Things Weigh? Newton: Weight proportional to Mass Einstein: Energy related to Mass Neither explained0origin of Mass Where do the masses come from? Are masses due to Higgs boson? (the physicists’ Holy Grail) The Seminal Papers The Englert-Brout-Higgs Mechanism Englert & Brout Guralnik, Hagen & Kibble The Higgs Boson • Higgs pointed out a massive scalar boson • “… an essential feature of [this] type of theory … is the prediction of incomplete multiplets of vector and scalar bosons” • Englert, Brout, Guralnik, Hagen & Kibble did not comment on its existence • Discussed in detail by Higgs in 1966 paper Mysterious Higgs Potential Mass2 of Higgs ~ curvature of potential at minimum Vertical scale ~ 1060 × dark energy A Phenomenological Profile of the Higgs Boson • • • • • • • • Neutral currents (1973) Charm (1974) Heavy lepton τ (1975) Attention to search for W±, Z0 For us, the Big Issue: is there a Higgs boson? Previously ~ 10 papers on Higgs bosons MH > 18 MeV First attempt at systematic survey A Phenomenological Profile of the Higgs Boson • Higgs decay modes and searches in 1975: Higgs Boson placed on the Experimental Agenda • Searches at LEP: (EG, Yellow report 76-18) • e+e- Z + H (EGN 76, Ioffe & Khoze 76, Lee, Quigg & Thacker 77) • Z H + μ+μ(EG 76, Bjorken 1976) • LEP: MH > 114.4 GeV The State of the Higgs in Mid-2011 • High-energy search: – Limit from LEP: mH > 114.4 GeV • High-precision electroweak data: – Sensitive to Higgs mass: mH = 96+30–24 GeV • Combined upper limit: mH < 161 GeV, or 190 GeV including direct limit • Exclusion from high-energy search at Tevatron: mH < 158 GeV or > 173 GeV Latest Higgs Searches @ Tevatron Experimental upper limit Standard Model prediction Exclude (100,109); (156,177) GeV Higgs Hunting @ LHC: Status th reported on Dec. 13 , 2011 Exclude 127 to 600 GeV Exclude 112.7 GeV to 115.5 GeV, 131 GeV to 237 GeV, 251 GeV to 453 GeV Has the Higgs Boson been Discovered? Interesting hints around Mh = 125 GeV ? CMS sees broad enhancement ATLAS prefers 125 GeV Has the Higgs Boson been Discovered? Interesting hints around 125 GeV in both experiments - but could also be 119 GeV ? ATLAS Signals • • • • γγ: 2.8σ ZZ: 2.1σ WW: 1.4σ Combined: 3.6σ CMS Signals • Combined: 2.6σ Has the Higgs Boson been Discovered? Unofficial blogger’s combination NOT ENDORSED BY EXPERIMENTS but he was right last time ! Combining the Information from Previous Direct Searches and Indirect Data Assuming the Standard Model mH = 125 ± 10 GeV mH = 124.5 ± 0.8 GeV Erler: arXiv:1201.0695 There be New Physics viXramust Blogger’s Combination th Data Model Beyondofthe Standard Dec.13 Higgs potential collapses Higgs coupling less than in Standard Model Precision Electroweak data?? Higgs coupling blows up!! Heretical Interpretation of EW Data What attitude towards LEP, NuTeV? Do all the data tell the same story? e.g., AL vs AH Chanowitz What most of us think Higgs + Higher-Order Operators Precision EW data suggest they are small: why? But conspiracies are possible: mH could be large, even if believe EW data …? Barbieri, Strumia Do not discard possibility of heavy Higgs Corridor to heavy Higgs? Elementary Higgs or Composite? • Higgs field: <0|H|0> ≠ 0 • Quantum loop problems • Fermion-antifermion condensate • Just like QCD, BCS superconductivity Cutoff Λ = 10 TeV • Top-antitop condensate? needed mt > 200 GeV Cut-off Λ ~ 1 TeV with Supersymmetry? New technicolour force? inconsistent with precision electroweak data? Interpolating Models • Combination of Higgs boson and vector ρ • Two main parameters: mρ and coupling gρ • Equivalently ratio weak/strong scale: g ρ / mρ Grojean, Giudice, Pomarol, Rattazzi What if the Higgs is not quite a Higgs? • Tree-level Higgs couplings ~ masses – Coefficient ~ 1/v • Couplings ~ dilaton of scale invariance • Broken by Higgs mass term –μ2, anomalies – Cannot remove μ2 (Coleman-Weinberg) – Anomalies give couplings to γγ, gg • Generalize to pseudo-dilaton of new (nearly) conformal strongly-interacting sector • Couplings ~ m/V (V > v?), additions to anomalies A Phenomenological Profile of a Pseudo-Dilaton • New strongly-interacting sector at scale ~ V • Pseudo-dilaton only particle with mass << V • Universal suppression of couplings to Standard Model particles ~ v/V Compilation Updated ofwith constraints Dec. 11 • Γ(gg) may be enhanced constraints • Γ(γγ) may be suppressed • Modified self-couplings • Pseudo-baryons as dark matter? 1000 900 800 V (GeV) 700 600 500 400 precision data 300 N =3 g 200 100 Campbell, JE, Olive: arXiv:1111.4495 200 300 400 m (GeV) 500 600 700 Higgsless Models? • Four-dimensional versions: Strong WW scattering @ TeV, incompatible with precision data? • Break EW symmetry by boundary conditions in extra dimension: delay strong WW scattering to ~ 10 TeV? Kaluza-Klein modes: mKK > 300 GeV? compatibility with precision data? • Warped extra dimension + brane kinetic terms? Lightest KK mode @ few 00 GeV, strong WW @ 6-7 TeV Theoretical Constraints on Higgs Mass • Large Mh → large self-coupling → blow up at low-energy scale Λ due to LHC 95% exclusion renormalization • Small: renormalization due to t quark drives quartic coupling < 0 at some scale Λ → vacuum unstable • Vacuum could be stabilized by supersymmetry Espinosa, JE, Giudice, Hoecker, Riotto, arXiv0906.0954 SUSY vs Data • Electroweak precision observables • Flavour physics observables • gμ - 2 • Higgs mass • Dark matter • LHC MasterCode: O.Buchmueller, JE et al. 68% & 95% CL contours ….. pre-LHC ___ LHC 1/fb Higgs mass χ2 price to pay if Mh = 125 GeV is < 2 Buchmueller, JE et al: arXiv:1112.3564 Favoured values of Mh ~ 119 GeV: Range consistent with evidence from LHC ! 68% & 95% CL contours ….. pre-Higgs ___ Higgs @ 125 Buchmueller, JE et al: arXiv:1112.3564 Gluino mass --- pre-Higgs ___ Higgs @ 125 … H@125, no g-2 Buchmueller, JE et al: arXiv:1112.3564 Favoured values of gluino mass significantly above pre-LHC, > 2 TeV The Stakes in the Higgs Search • How is gauge symmetry broken? • Is there any elementary scalar field? • Would have caused phase transition in the Universe when it was about 10-12 seconds old • May have generated then the matter in the Universe: electroweak baryogenesis • A related inflaton might have expanded the Universe when it was about 10-35 seconds old • Contributes to today’s dark energy: 1060 too much! Measurements of Higgs Couplings • Some decays limited by statistics • Others limited by systematics The Spin of the Higgs Boson @ LHC Low mass: if H →γγ, It cannot have spin 1 Higher mass: angular correlations in H → ZZ decays Higgs Self-coupling @ Hi-Lumi LHC? Measure triple-Higgs-boson coupling with accuracy comparable to 0.5 TeV ILC? Awaits confirmation by detailed experimental simulation The Fun is just Beginning • LHC7 may well resolve Higgs issue • LHC7 (or 8) unlikely to resolve SUSY issue (or other BSM scenarios) • Premium on increasing Ecm towards 14 TeV • Prospects for L factor 500 with Hi-Lumi LHC • What will follow the LHC? – Higgs factory? CLIC? High-E LHC? • A new era about to open: AH (anno Higgsi) Quo Vadis gμ - 2? • Strong discrepancy between BNL experiment and e+e- data: – now ~ 3.6 σ – Better agreement between e+e- experiments • Increased discrepancy between BNL experiment and τ decay data – now ~ 2.4 σ – Convergence between e+eexperiments and τ decay • More credibility? MSSM: > 100 parameters Minimal Flavour Violation: 13 parameters (+ 6 violating CP) SU(5) unification: 7 parameters NUHM2: 6 parameters NUHM1 = SO(10): 5 parameters CMSSM: 4 parameters mSUGRA: 3 parameters String? … nevertheless Supersymmetric Dark Matter in View of 1/fb of LHC Data 68% & 95% CL contours ….. pre-LHC ___ LHC 1/fb MasterCode: O.Buchmueller, JE et al. Impact of dropping gμ-2 constraint ….. pre-LHC ___ LHC 1/fb MasterCode: O.Buchmueller, JE et al. Dropping gμ - 2 allows masses up to dark matter limit Gluino mass ….. pre-LHC ___ LHC 1/fb MasterCode: O.Buchmueller, JE et al. Favoured values of gluino mass significantly above pre-LHC, > 1 TeV + LHCb Bs μ+μ- ….. pre-LHC ___ LHC 1/fb --- with CDF MasterCode: O.Buchmueller, JE et al. Favoured values of BR(Bs μ+μ-) above SM value ! (due to increase in tan β) Higgs mass Favoured values of Mh ~ 119 GeV: Coincides with value consistent with LHC ! Generic Little Higgs Models (Higgs as pseudo-Goldstone boson of larger symmetry) Loop cancellation mechanism Little Higgs Supersymmetry Little Higgs Models • Embed SM in larger gauge group • Higgs as pseudo-Goldstone boson • Cancel top loop with new heavy T quark • New gauge bosons, Higgses MT < 2 TeV (mh / 200 GeV)2 MW’ < 6 TeV (mh / 200 GeV) • Higgs light, other new MH++ < 10 TeV physics heavy Not as complete as susy: more physics > Searches for Extra Particles in Little Higgs Models Estimates of mH from different Measurements Spread looks natural: no significant disagreemen Intermediate Models Effects on Higgs Decays • Dependences on of Higgs branching ratios • Standard Model recovered in limit 0 Grojean, Giudice, Pomarol, Rattazzi What if no Higgs? • Higgs must discriminate between different types of particles: – Some have masses, some do not – Masses of different particles are different • In mathematical jargon, symmetry must be broken: how? – Break symmetry in equations? – Or in solutions to symmetric equations? • This is the route proposed by Higgs – Is there another way? Where to Break the Symmetry? • Throughout all space? – Route proposed by Higgs – Universal Higgs (snow)field breaks symmetry – If so, what type of field? • Or at the edge of space? – Break symmetry at the boundary? • Not possible in 3-dimensional space – No boundaries – Postulate extra dimensions of space • Different particles behave differently in the extra dimension(s) Higgs Hunting @ Tevatron Exclude (100,109); (156,177) GeV Comparison between Weakly- and Strongly-coupled Models XENON100 & other Experiments Aprile et al: arXiv:1104.2549 Supersymmetry Searches in ATLAS Jets + missing energy + 0 lepton XENON100 Experiment Aprile et al: arXiv:1104.2549 Early Phenomenological Bounds • Emission from stars: MH > 0.7 me (Sato & Sato, 1975) • Neutron-electron scattering: MH > 0.7 MeV (Rafelski, Muller, Soff & Greiner; Watson & Sundaresan; Adler, Dashen & Treiman; 1974) • Neutron-nucleus scattering: MH > 13 MeV (Barbieri & Ericson, 1975) • Nuclear 0+ – 0+ transitions: MH > 18 MeV (Kohler, Watson & Becker, 1974) Supersymmetry Searches @ LHC Jets + missing energy (+ lepton(s)) Applicable to NUHM, CMSSM, VCMSSM, mSUGRA but need other strategies for other models