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?