Higgs, Less Higgs, Higgsless or more Higgs?

1. Higgs, Less Higgs, Higgsless or more Higgs? ITEP Winter School Otradoe, February 2012 John Ellis, King’s College London & CERN

2. Plan of the Lectures • The Higgs boson in the Standard Model • Less Higgs or Higgsless? • Higgs and Supersymmetry

3. Summary of the Standard Model • Particles and SU(3)× SU(2)× U(1) quantum numbers: • Lagrangian: gauge interactions matter fermions Yukawa interactions Higgs potential

4. 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?

5. Precision Tests of the StandardModel Lepton couplings Pulls in global fit

6. 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?

7. Where • do • the • masses • come from • ? • Why do Things Weigh? • Newton: • Weight proportional toMass • Einstein: • Energy related toMass • Neither explained origin of Mass • 0 • Are masses due to Higgs boson? • (the physicists’ Holy Grail)

9. 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

10. The Higgs Mechanism • Postulated effective Higgs potential: • Minimum energy at non-zero value: • Non-zero masses: • Components of Higgs field: • π massless, σ massive:

11. 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:

12. The Seminal Papers

13. 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)

14. The Englert-Brout-Higgs Mechanism Englert & Brout Guralnik, Hagen & Kibble

15. 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

16. Nambu, EB, GHK and Higgs Spontaneous breaking of symmetry

17. 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

18. Higgs decay modes and searches in 1975: A Phenomenological Profile of the Higgs Boson

19. Higgs Decay Branching Ratios • Couplings proportional to mass: • Decays into heavier particles favoured • But: important couplings through loops: • gluon + gluon → Higgs →γγ

20. 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!

21. 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

22. Combining the Information from Previous Direct Searches and Indirect Data mH = 125 ± 10 GeV Gfitter collaboration

23. Latest Higgs Searches @ Tevatron Experimental upper limit Standard Model prediction Exclude (100,109); (156,177) GeV

24. A la recherche du Higgs perdu … Higgs Production at the LHC

25. Higgs Hunting @ LHC: Status on Feb. 8th, 2012 Exclude 112.9 GeV to 115.5 GeV, 131 GeV to 238 GeV, 251 GeV to 466 GeV Exclude 127 to 600 GeV

26. Has the Higgs been Discovered? Interesting hints around Mh = 125 GeV ? ATLAS prefers 125 GeV CMS sees broad enhancement

27. ATLASSignals • γγ: 2.8σ • ZZ: 2.1σ • WW: 1.4σ • Combined: 3.5σ

28. CMS Signals Combined: 3.1 σ

29. Are ATLAS & CMS seeing the Same Thing? Both compatible with mH = 125 GeV

30. Has the Higgs Boson been Discovered? Evolution of signal from Dec. 2011 to Feb. 2012

31. Has the Higgs Boson been Discovered? Unofficial blogger’s combination NOT ENDORSED BY EXPERIMENTS but he was right last time !

32. 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

33. 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

34. 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

35. Measuring Higgs Couplings @ LHC Current LHC hint @ Mh = 125 GeV

36. For Mh = 120 GeV Higgs Measurements @ LHC &ILC

37. STANDARD MODEL