Where to Search for the Higgs

1. Where to Search for the Higgs • A direct search for the Higgs was carried out by the four LEP experiments from 1995-2000 • CMS energy of 205-208 GeV • The production and decay was primarily by

2. Where to Search for the Higgs • The combined result was • Of course there were interesting events

3. Where to Search for the Higgs • “Triviality” sets an upper bound on the Higgs mass of O(1 TeV)

4. Where to Search for the Higgs • “Triviality” sets an upper bound on the Higgs mass of O(1 TeV)

5. Where to Search for the Higgs • Another upper limit can be found by considering the scattering amplitudes for • Partial wave unitarity yields

6. Where to Search for the Higgs • Indirect constraints on the Higgs mass can be found by considering electroweak radiative corrections like

7. Where to Search for the Higgs • Electroweak observables depend quadratically on the top quark mass and logarithmically on the Higgs boson mass • A global fit yields

8. Where to Search for the Higgs • Recently the DZero and CDF experiments at the Fermilab Tevatron excluded a new mass region • Many different channels

9. LHC (Large Hadron Collider) • CERN is located outside Geneva, Switzerland • The energy of the LHC will be 7 TeV x 7 TeV • The ring circumference is 27 km 9

10. LHC Complex • Duoplasmatron at 300mA beam current at 92 keV • RFQ to 750 keV • Linac 2 to 50 MeV • PSB to 1.4 GeV • PS to 28 GeV • SPS to 450 GeV • LHC to 7 TeV at 180mA beam current

11. What is the B Field? • You might recall from your study of E&M that a particle of momentum p in a uniform magnetic field B undergoes circular motion with radius r • The LHC circumference is ~27 km • Packing fraction of ~64% gives R~2.8 km • Thus B needed for p=7 TeV is ~8.3 T • Superconducting magnets using superfluid He at 1.8K are needed to reach this field • Magnet current at this field is 11850 A • Bending achieved by 1232 15-m dipoles 11

12. LHC Dipole

13. LHC Accelerator LHC dipoles 13

14. LHC Dipoles • Coils

15. LHC Accelerator LHC RF cavities RF = 400 MHz Rev f = 11246 Hz 15

16. LHC Magnets • September 19, 2008 • During powering tests, a fault occurred in the electrical bus connections between a dipole and quadrupole in Sector 3-4 • The power supply tripped off due to a resistive zone and magnet quenches were triggered • An electrical arc developed that punctured the helium enclosure and led to the release of helium into the vacuum of the cryostat • The vacuum enclosure could not contain the pressure rise resulting in large pressure forces acting on the vacuum barriers separating subsectors

17. September 19th Incident • The connecting busbar

18. September 19th Incident • The electrical arc destroyed the busbars

19. September 19th Incident • The large pressure forces resulted in magnet displacements

20. September 19th Incident • And more magnet displacements

21. September 19th Incident • As well as broken ground supports

22. September 19th Incident • And beam vacuum contamination

23. Repairs • A total of 53 magnets (39 dipoles and 14 SSS) were removed and repaired • The number and size of relief valves on the cryostat vacuum vessels will be increased • Designed to cope with a He discharge x2 the September 19th incident • An enhanced quench detection and protection system (QPS) was developed to include interconnects and busbar splices • Floor jacks were reinforced on some quadrupoles

24. Schedule • Schedule as of February 09 • Beam in late September • Collisions in late October • 8-10 TeV run through autumn 2010 • Experts say scheduled is tight but realistic • Allows completion of all repairs • Applies more stringent safety constraints • Acknowledges helium storage and transfer constraints

25. Higgs Production at the LHC • Gluon Fusion (GGF) • Dominant process • Vector Boson Fusion (VBF) • Second largest cross section • Distinctive topology useful for small mH • Associated W/Z (AW) • Associated Top (AT) • Interesting topologies but smaller cross section

26. Higgs Production at the LHC GGF VBF AW AT

27. Jet Jet Forward jets f h Higgs Decay VBF (Vector Boson Fusion) • Higgs production with a distinctive topology • Forward jets • No central activity because no color

28. Higgs Decay Modes • The mass of the Higgs is unknown but the decay of the properties of the Higgs is a known • The Higgs boson likes mass • It couples to particles proportional to their mass • It decays preferentially to the heaviest particles kinematically allowed

29. Higgs Decay Modes

30. Higgs Decay Modes • The Standard Model rules say the Higgs decays preferentially into the heaviest pair of particles that is kinematically allowed

31. Higgs Production at the Tevatron

32. Higgs Production at the LHC

33. Higgs Decay Modes

34. Cross Sections at the LHC Resonances - narrow width approximation: e.g. LHC Cross Sections: There is a factor > 1010 between the Higgs cross section and the total inelastic cross section. There is also the final state branching fraction to consider. This is why the LHC design luminosity is so high.

35. LHC Dipole Interconnections

36. Kugelstossen: The energy of one shot (5 kg) at 800 km/hour corresponds to the energy stored in one bunch at 7 TeV. There are 2808 bunches. Factor 200 compared to HERA, TEVATRON and SPS. shot Energy stored in one beam at 7 TeV: 362 MJoule

37. Particle Accelerators • We study nature by using high energy collisions between particles • Particle accelerators can be thought of as giant microscopes that are used to study extremely small dimensions • The higher the energy the smaller the wavelength the better the resolution • Particle detectors are used to record the results of these high energy collisions 37

38. LHC FODO

39. LHC Accelerator LHC dipoles 39

40. LHC

41. LHC The experiments (detectors) are located 100m underground 41

42. LHC Accelerator

43. LHC Accelerator At four points around the ring the two beams are brought together where collisions occur The beams are actually composed of many “bunches” of protons These bunch crossings (collisions) occur every 25 ns At an energy of 7 TeV it takes 90μs for a proton to make one revolution 43

44. Higgs Boson Discovery Unknown unknowns 44