RECAST’ing light Higgs searches @ ALEPH

1. RECAST’ing light Higgs searches @ ALEPH Itay Yavin NYU With James Beacham and Kyle Cranmer for the ALEPH collaboration 0901.0283 (with spiritual support from N. Weiner) JHU

2. Content • Search for a light Higgs-boson • RECAST - Request Efficiency Calculationfor AlternativeSignal Testing JHU

3. Well…, not exactly, we actually don’t really know what is the origin of most of the mass in the universe. Matter and Mass “The Higgs boson is the only Standard Model particle that has not been observed. Experimental detection of the Higgs boson would help explain the origin of mass in the universe.” Wikipedia - source of all knowledge… JHU

4. Actually, most of the mass of the atom comes from the protons and neutrons in the nucleus. The mass of those is almost entirely the result of the potential energy of the strong force that binds the quarks together. A true manifestation of Einstein’s M = E/c2 Matter and Mass “Oh, you are just being facetious, we mean the origin of mass for the 4% of the universe we are actually made of … “ JHU

5. Vector-Boson Scattering The physical Higgs is responsible for taming the divergence in the vector-bosons scattering amplitude. JHU

6. Where is Higgs? JHU

7. Higgs Searches The most extensive search was made in the Higgs to di-bottom channel, LEP combined search - hep-ex/0306033v1 JHU

8. Electroweak Precision Tests JHU

9. Higgs@98 ? See Dermisek and Gunion, hep-ph/0510322. Also Drees hep-ph/0502075 2.3  evidence for mh ~ 98 GeV. Also a 1.7  evidence for higgs at 115 GeV. JHU

10. Choosing between two evils From M. Chanowitz 0806.0890 JHU

11. Supersymmetric Higgs In the minimal Supersymmetric Standard Model (MSSM), at tree level the higgs is predicted to be lighter than the Z0 boson(1), Higgs Hunter’s Guide, circa 1989. . . (1)Recall 2HDM and the MSSM has two Higgs field and the ratio of the vacuum expectation value is, JHU

12. A Conundrum (a.k.a the LEP paradox) There seems to be this tension between the direct production results which favor heavy Higgs, to the indirect probes/theory bias which favors a lighter Higgs … Heavy Higgs Light Higgs JHU

13. Escaping the LEP Bounds If Higgs decays in a non-standard way, it may have escaped detection. One of the most motivated examples is Higgs to four tau’s, Dermisek and Gunion, hep-ph/0502105 JHU

14. The decay into the pseudo-scalars can easily dominate, See e.g. Chang et al. 0801.4554 Dimensionless number related to the h-a-a coupling Higgs Decay The Higgs boson likes to decay into Bottoms, because the Bottom’s Yukawa coupling is the largest among the accessible fermions. But, it’s pretty small and easy to overcome, JHU

15. 4 Fermion Final State Kinematically accessible region which hasn’t been searched Also, A. Haas at Tevatron constrained decays into muons! [hep-ex] 0905.3381 (see Lisanti and Wacker for theory [hep-ph] 0903.1377 JHU

16. Closing the Window Here is what J. Gunion thinks: So we set out to discover the Higgs… or at least close this window. JHU

17. JHU

18. LEP and ALEPH JHU

19. The ALEPH detector Tracking: silicon + large time projection chamber (~31 hits) ECAL: lead + proportional wire chambers, 22X0 1.5 T HCAL: 23 layers of iron yolk + streamer tubes muons identified via HCAL+2 muon chambers Detector simulation based on Geant 3, analysis based on 10 year old fortran framework JHU

20. Expected Number of Events Have enough events for discovery up to ~ 90 GeV (depending on a mass) JHU

21.  Event Topology Since the Higgs is rather heavy and the pseudo-scalar light, it is fairly boosted in the lab frame. Therefore, the resulting tau’s are very collimated and so are their decay products … We designed three different searches depending on the decay of the Z boson. Before describing these in detail, let’s examine the resulting jets. JHU

22. Simulated signal event 2 back-to-back electrons clearly distinguished from 2 back-to-back jets. not much else in the event (about 50 GeV of missing energy) JHU

23. J1 Demand a beam-jet isolation cut, to make sure we are not missing tracks. J2 Jets We used the Jade algorithm to form jets with a given invariant mass. Beam axis  decays “1-prong” 85.36%, “3-prong” 14.56% Each Jet contains 2,4, or 6 tracks from the 2 tau decays. This forms a powerful discreminant. JHU

24. Backgrounds We formed several control samples, where no signal is expected in order to test our Monte-Carlo simulations. JHU

25. Control Samples We had to make sure that the MC is describing the background correctly. But, we wanted to keep a blind analysis so we defined a few control samples, Exclude di-lepton invariant mass around mZ, kills the signal. #track < 1 (kills anything with more than one track). Z-> di-lepton, MJJ inv < 60 GeV Z-> invisible, exclude on MET > 80 GeV #track > 6 in both jets AND MJJ < 60 GeV JHU

26. Unboxing We were aiming for discovery… Champagne, just in case… JHU

27. Results JHU

28. Exclusion Limits JHU

29. Ruling out a hidden Higgs? JHU

30. Still hiding? By lowering the branching ratio to taus, one can still hide the Higgs in the mixed decay channel. That’s what we are going after next, This makes things more difficult, but by using jet substructure we are hopeful we can reduce the background and exclude this possibility as well. JHU

31. More Analysis • Mixed channels • Higgs to gluons/charms? • Higgs to Lepton Jets? (Falkowski, Ruderman, Volansky, Zupan) JHU

32. Provocative… From M. Chanowitz 0806.0890 From 1005.2757 JHU

33. RECAST Request Efficiency Calculationfor AlternativeSignal Testing JHU

34. BSM Physics • Many new models of beyond the Standard Model physics have been suggested: • SUSY – SUGRA,GMSB,AMSB,… • RS • UED • Little Higgs • Many powerful tools were created to allow fast incorporation and simulation of new particle physics, • Madgraph/Madevent • Calchep/Comphep • PYTHIA,HERWIG • LHE format Can we use all these new tools to ‘quickly’ limit the new theories? (This is, if you like, a complementary question to the one N. Toro posed yesterday, that of characterization of new physics in the case of discovery)

35. Reporting an Experimental Search Alice Signal independent Experimentalist Signal dependent Alice is searching for some signal and reports an exclusion plot based on that signal. The cuts and procedure she employs leads to some signal efficiency which she quotes. JHU

36. Sometimes in the Future… Bob Bob wants to search for a different signal. But, maybe Alice’s search already covers his signal in certain regions of the parameter space. If that is true Bob’s job is made much simpler, he can concentrate on these regions which are not already excluded by Alice’s analysis… But how will Bob know? He needs to know what is the efficiency of Alice’s search for his new signal! Experimentalist Carol Carol just thought of a new particle that can explain all sorts of things. But, she realizes that this particle may result in a signal which, while not the same as Alice’s, does have some overlap with it. Maybe it’s already excluded by Alice’s analysis. . . How will Carol know? She needs to know what is the efficiency of Alice’s search for her new signal! Theorist JHU

37. RECAST Request Efficiency Calculationfor AlternativeSignal Testing Alice’s analysis code including all the cuts, detector effects and etc. Seen only by Alice Can be submitted by everyone Seen by everyone, no data, no code, only efficiency LHE New signal Efficiency for new signal

38. Everyone Benefits!!! Alice • More impact for Alice’s search!!! • Alice does not have to worry about interpreting her results under many different signal assumptions. Bob • Bob can use Alice’s results to make sure the new signal he is planning to search for is not already excluded. • Maybe some regions of his new signal are excluded, so concentrate and optimize his analysis to those which are not! Experimentalist Carol • Carol can confidently estimate the coverage of Alice’s analysis on her new model. • Help to direct the theorist thinking into these regions not already excluded even when considering new models which have not been explicitly searched for. Theorist

39. Examples The buried/charmed Higgs scenarios of Csaki et al. (0906.3026, 0910.3210) could have been easily constrained by RECASTing existing Higgs to 2 jets flavor independent analyses. Meade, Reece, and Shih (0911.4130) derived limits on prompt decays of general neutralino NLSPs at Tevatron using the limited existing analysis available. Their efforts could have been greatly reduced with RECAST. Falkwoski et al. suggested hiding the Higgs boson through Higgs to lepton-jets. Again, RECASTing existing analyses could have helped in placing better limits on this scenario.

40. The End JHU

41. What is a? If other scalar fields aside from the Higgs field are present, then the pseudo-scalar component can be naturally light (pseudo-Nambu-Goldstone boson). This happens in extensions of the SM, such as MSSM, and/or NMSSM… This Lagrangian contains a vertex allowing the Higgs to decay into two a’s JHU

42. a Decay The pseudo-scalar decays back to SM fermions through its mixing with the Higgs and hence it will decay to the heaviest fermions kinematically accessible. Below the bottom meson threshold, the pseudo-scalar likes to decay to tau’s JHU

43. OPAL Search OPAL collaboration, hep-ex/0209068 JHU

44. Higgs Production JHU

45. coded track multiplicity in signal backgrounds Track Multiplicity Each Jet contains 2,4, or 6 tracks from the 2 tau decays. This forms a powerful discreminant. JHU

46. Analysis JHU

47. Analysis Both the muon and electron channel tend to involve extra photons in the final state which must be taken into account to correctly reconstruct the Z. JHU

48. Analysis JHU

49. Expected Signficance The lower reach at higher a masses is due to lower signal efficiency. We are presently correcting this and the reach should improve. JHU

50. Event Counts JHU