Mike Bisset / 毕楷杰 Tsinghua University Beijing, China

1. SUSY Higgs at the LHC plus a bit more Mike Bisset / 毕楷杰 Tsinghua University Beijing, China “Linear Collider” conference Tsinghua, July 17, 2005

2. First consider something that isNOT supersymmetry --- MUED’s Minimal universal extra dimensions H.-C. Cheng, Matchev & Schmaltz hep-ph/0205314 All SM fields propagate in a single compactified extra dimension with compactification radius near the TeV scale  All SM particles have KK partners with similar couplings (lowest energy states in the Kaluza-Klein towers)  The lowest KK level particles carry a conserved quantum number KK-parity  The lightest KK particle is the stable LKP The LKP is not detected, resulting in a missing energy signal. Sounds a lot like the MSSM, no?

3. Distinctions between the MSSM and MUED’s  Sparticles have different spins from their SM partners while KK particles have the same spin This would certainly be testable at a LC, but at the LHC maybe not limited attempts: Barr, hep-ph/0405052 Smillie & Webber hep-ph/0507171  There is no analog to the heavier MSSM Higgs bosons The KK partners to the Higgs carry KK-parity, and so should be pair produced (behaving more like Higgsinos than like Higgs bosons)

4. So we see detection of the heavier MSSM Higgs bosons is crucial for even being sure that we are seeing SUPERSYMMETRY

5. How well can we do at the LHC?

6. ATLAS TDR

7. the only detect ‘decoupling regime’

8. BUT depends on good detection capabilities for b’s and tau’s signals only detect LEP II excluded

9. Depends on good detection capabilities for b’s and tau’s only detect Gold -plated signal LEP II excluded

10. BUT the preceding does not take into account possible Higgs boson decays into sparticles On the bad side… decays to these channels reduce the rates of SM signal channels new signals may be found On the good side…

11. One channel that has received some attention is: 4 leptons + signature (2 OS same-flavor pairs) But if such a signal is observed, is it really from this decay chain? (assumption in several studies thus far)

12. M (GeV) from gaugino unification 2 light sleptons

13. M (GeV) 2

14. M (GeV) 2

16. in mSUGRA Now what about non-Higgs boson ‘backgrounds’? hello

17. Dependence on sleptons Now what about non-Higgs boson ‘backgrounds’? hello

18. Now what about non-Higgs boson backgrounds? Now what about non-Higgs boson ‘backgrounds’? SM backgrounds can be eliminated mainly through cut coupled with final state hello Other SUSY processes?

19. Let’s try to think more generally for a while … Now what about non-Higgs boson backgrounds? Look at processes of the type other stuff Pair production of new heavy states Decay to SM fermion pairs Required by some new symmetry of the SM extension e.g.’s: KK-parity in MUED’s R-parity in SUSY   conservation Z2  -symmetry T-parity in little Higgs models Hubisz & Meade hep-ph/0411264

20. SUPERSYMMETRY MSSM with R-parity conservation LSP is stable and invisible other stuff Here we take (-ino for short)

21. At LHC, can have other stuff but also How much of each? Depends on parameters of the model

22. LHC will also have lots of SM QCD backgrounds  a nice choice is to take & (assuming –ino leptonic BRs adequate) Alternatives: other stuff

23. Facts of life at the LHC: At hadron collider, cannot set energy for the parton-level process unlike at a linear collider where one can scan up incrementally in to cross each threshold sequentially one at a time So just must deal with different states being produced simultaneously at different rates Need to disentangle these

24. Production modes: ‘direct’ Higgs-mediated colored-sparticle cascade decays Rates generally small Rates may be large if heavier MSSM Higgs bosons are in the right zone Largest potential rates due to strong production cross-sections Especially if gluinos (and squarks) are relatively light.

25. Study such processes at the LHC via a technique reminiscent of Dalitz Plots Though disappearing LSP precludes looking for resonance bumps, we can look for endpoints.

26. Dalitz plots R.H. Dalitz Phil. Mag. 44 (1953) 1068 E. Fabri Nuovo Cimento 1 (1953) 479 Originally designed to determine the spin and parity of newly-discovered mesons by examining their decays into 3 pions vector meson

27. Later modified for use in Resonance hunting e.g., Shafer et al. PRL 10 (1963) 176 & M. Ferro Luzzi et al., Nuovo Cimento 36 (1965) 1101 Clearly see the resonance in scattering

28. And still in use today: BABAR hep-ex/0507026 Crystal Ball hepex/9708025 But apparently not meaningfully applied to SUSY or beyond the SM applications BELLE, Belle-Conf-0410 …until now?

29. Topologies onDalitz-like plot for our process types box-like shape for production wedge-like shape for production

30. Possible Dalitz-like Plots: Could be or or

31. Complications  other stuff NO Assumes other stuff NO  just other stuff (no leptons) Typically these decay modes are small to negligibly tiny. Neglects charginos   Along with leptons from decaying top quarks that might happen to be produced. These chargino channels sub-leading at worst

32. First consider production processes with the largest rates… Gluino/squark pair production with cascade decays

33. Salient points about (c): Produces jets, cannot be hadronically quiet  No fundamental vertex   each –ino produced independently reduction in number of possible patterns possible on Dalitz-like plots IF -ino pair production is only due to gluinos

34.  Know and rates know rate. (or only one kind of colored sparticle) But squarks can also contribute significantly!!

35.  Beenacker et al., NPB 492(1997) 51

36. Sleptons relatively light to enhance leptonic BRs EW gaugino unification  endpoints become bands

39. charginos!!! Note: these are inclusive 4-lepton rates with no cuts

40. From Table can determine relative rates for different –ino pairs Point C: Now actually simulate signals and backgrounds with HERWIG 6.5 event generator coupled to realistic calorimeter simulation package (recent CMS package)

41. Simple set of CUTS Note: lose up to 90% of inclusive 4-lepton events mostly due to one or more leptons being too soft.

42. Resulting Dalitz-like plots envelope-types MSSM Point A

43. MSSM Point A Hard edges 3-body decay  off-shell sleptons very important

44. MSSM Point A Here sleptons on mass-shell  two-body decays End points no longer -ino mass differences

45. MSSM Point A Note change in event density around “stripe” or a other stuff 22.8% of the time

46. MSSM Point A “maverick events” These events cannot be accounted for within the framework of our modeling for the Dalitz-like plot Study of the detailed HERWIG output for such generated events confirmed that leptons in these events come from charginos in addition, there were other exceptional features of these points

47. MSSM Point B envelope-types

48. MSSM Point B Double the luminosity Two heavy –inos very close in mass

49. MSSM Point B Note: squark production is required to account for these events Can get a clean sample of events only coming from squarks, not gluinos.

50. MSSM Point C envelope-types