Create Presentation
Download Presentation

Physics beyond the Standard Model: Higgs and Supersymmetry – Why, what, where and how?

Physics beyond the Standard Model: Higgs and Supersymmetry – Why, what, where and how?

112 Views

Download Presentation
Download Presentation
## Physics beyond the Standard Model: Higgs and Supersymmetry – Why, what, where and how?

- - - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - - -

**Physics beyond the Standard Model:Higgs and Supersymmetry**–Why, what, where and how? Nanyang Technological University Singapore, January 2012 John Ellis, King’s College London & CERN**Plan of the Lectures**• The Standard Model and issues beyond it • Origin of particle masses: Higgs boson or? • Supersymmetry • Searches for supersymmetry: LHC & dark matter**Summary of the Standard Model**• Particles and SU(3)× SU(2)× U(1) quantum numbers: • Lagrangian: gauge interactions matter fermions Yukawa interactions Higgs potential**Gauge Interactions of the Standard Model**• Three separate gauge group factors: • SU(3) × SU(2) × U(1) • Strong × electroweak • Three different gauge couplings: • g3, g2, g ́ • Mixing between the SU(2) and U(1) factors: • Experimental value: sin2θW = 0.23120 ± 0.00015 Clue for Grand Unification and supersymmetry**Weak Interactions**• Interactions of lepton doublets: • Charged-current interactions: • Neutral-current interactions: • Mixing between quark flavours:**Status of the Standard Model**• Perfect agreement with all confirmedaccelerator data • Consistency with precision electroweak data (LEP et al) only if there is a Higgs boson • Agreement seems to require a relatively light Higgs boson weighing < ~ 180 GeV • Raises many unanswered questions: mass? flavour? unification?**Precision Tests of the StandardModel**Lepton couplings Pulls in global fit**Parameters of the Standard Model**• Gauge sector: • 3 gauge couplings: g3, g2, g ́ • 1 strong CP-violating phase • Yukawa interactions: • 3 charge-lepton masses • 6 quark masses • 4 CKM angles and phase • Higgs sector: • 2 parameters: μ, λ • Total: 19 parameters Unification? Flavour? Mass?**Susy**Susy Susy Open Questions beyond the Standard Model • What is the origin of particle masses? due to a Higgs boson? + other physics? solution at energy < 1 TeV (1000 GeV) • Why so many types of matter particles? matter-antimatter difference? • Unification of the fundamental forces? at very high energy ~ 1016 GeV? probe directly via neutrino physics, indirectly via masses, couplings • Quantum theory of gravity? (super)string theory: extra space-time dimensions?**Where**do the masses come from ? Why do Things Weigh? Newton: Weight proportional to Mass Einstein: Energy related to Mass Neither explained origin of Mass 0 Are masses due to Higgs boson? (the physicists’ Holy Grail)**Skier moves fast:**Like particle without mass e.g., photon = particle of light Think of a Snowfield Snowshoer sinks into snow, moves slower: Like particle with mass e.g., electron The LHC looks for the snowflake: the Higgs Boson Hiker sinks deep, moves very slowly: Particle with large mass**The Higgs Boson and Cosmology**• Changed the state of the Universe when it was about 10-12 seconds old • May have generated then the matter in the Universe • Contributes (too much) to today’s dark energy • A related inflaton might have expanded the Universe when it was about 10-35 seconds old**The Higgs Mechanism**• Postulated effective Higgs potential: • Minimum energy at non-zero value: • Non-zero masses: • Components of Higgs field: • π massless, σ massive:**Masses for Gauge Bosons**• Kinetic terms for SU(2) and U(1) gauge bosons: where • Kinetic term for Higgs field: • Expanding around vacuum: • Boson masses:**The Englert-Brout-Higgs Mechanism**• Vacuum expectation value of scalar field • Englert & Brout: June 26th 1964 • First Higgs paper: July 27th 1964 • Pointed out loophole in argument of Gilbert if gauge theory described in Coulomb gauge • Accepted by Physics Letters • Second Higgs paper with explicit example sent on July 31st 1964 to Physics Letters, rejected! • Revised version (Aug. 31st 1964) accepted by PRL • Guralnik, Hagen & Kibble (Oct. 12th 1964)**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**Nambu, EB, GHK and Higgs**Spontaneous breaking of symmetry**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**Higgs decay modes and searches in 1975:**A Phenomenological Profile of the Higgs Boson**Higgs Decay Branching Ratios**• Couplings proportional to mass: • Decays into heavier particles favoured • But: important couplings through loops: • gluon + gluon → Higgs →γγ**Constraints on Higgs Mass**• Electroweak observables sensitive via quantum loop corrections: • Sensitivity to top, Higgs masses: • Preferred Higgs mass: mH ~ 80 ± 30 GeV • Compare with lower limit from direct searches: mH> 114 GeV • No conflict!**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**Combining the Information from Previous Direct Searches and**Indirect Data mH = 125 ± 10 GeV • Gfitter collaboration**Latest Higgs Searches @ Tevatron**Experimental upper limit Standard Model prediction Exclude (100,109); (156,177) GeV**A la recherche du**Higgs perdu … Higgs Production at the LHC**Higgs Hunting @ LHC: Status reported on Dec. 13th, 2011**Exclude 112.7 GeV to 115.5 GeV, 131 GeV to 237 GeV, 251 GeV to 453 GeV Exclude 127 to 600 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 ?**ATLASSignals**• 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 !**Assuming the Standard Model**Combining the Information from Previous Direct Searches and Indirect Data mH = 125 ± 10 GeV mH = 124.5 ± 0.8 GeV Erler: arXiv:1201.0695**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**Do we already know the ‘Higgs’ has Spin Zero ?**• Decays into γγ, so cannot have spin 1 • 0 or 2? • If it decays into ττ or b-bar: spin 0 or 1 or orbital angular momentum • Can diagnose spin via angular correlations of leptons in WW, ZZ decays**For Mh = 120 GeV**Higgs Measurements @ LHC &ILC**There must be New Physics**Beyond the Standard Model • viXra Blogger’s Combination • of Dec.13th Data Higgs potential collapses Precision Electroweak data?? Higgs coupling blows up!! Higgs coupling less than in Standard Model**What attitude towards LEP, NuTeV?**Heretical Interpretation of EW Data Do all the data tell the same story? e.g., AL vs AH What most of us think Chanowitz**Estimates of mH from different Measurements**Spread looks natural: no significant disagreement**But conspiracies**are possible: mH could be large, even if believe EW data …? Higgs + Higher-Order Operators Corridor to heavy Higgs? Precision EW data suggest they are small: why? Do not discard possibility of heavy Higgs Barbieri, Strumia**Higgs field:**<0|H|0> ≠ 0 Quantum loop problems Fermion-antifermion condensate Just like QCD, BCS superconductivity Top-antitop condensate? needed mt > 200 GeV Elementary Higgs or Composite? • Cutoff • Λ = 10 TeV • New technicolour force? heavy scalar resonance? • inconsistent with precision electroweak data? • Cut-off Λ ~ 1 TeV with • Supersymmetry?**Interpolating Models**• Combination of Higgs boson and vector ρ • Two main parameters: mρ and coupling gρ • Equivalently ratio weak/strong scale: gρ / mρ Grojean, Giudice, Pomarol, Rattazzi**Generic LittleHiggs 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 • Higgs light, other new physics heavy MT < 2 TeV (mh / 200 GeV)2 MW’ < 6 TeV (mh / 200 GeV)2 MH++ < 10 TeV Not as complete as susy: more physics > 10 TeV**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 • Γ(gg) may be enhanced • Γ(γγ) may be suppressed • Modified self-couplings • Pseudo-baryons as dark matter? • Compilation • of constraints • Updated • with Dec. 11 • constraints • Campbell, JE, Olive: arXiv:1111.4495**Higgsless Models?**• Four-dimensional versions: Strong WW scattering @ TeV, incompatible with precision data? • Break EW symmetry by boundary conditions in extra dimension: delaystrong 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**Theorists getting Cold Feet**• Composite Higgs model? conflicts with precision electroweak data • Interpretation of EW data? consistency of measurements?Discard some? • Higgs + higher-dimensional operators? corridors to higher Higgs masses? • Little Higgs models? extra `Top’, gauge bosons, `Higgses’ • Higgsless models? strong WW scattering, extra D?