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Higgs decays to fermions in CMS (H  , H bb, a )

Higgs decays to fermions in CMS (H  , H bb, a ). Rainer Mankel Deutsches Elektronen Synchrotron (DESY) for the CMS Collaboration Standard Model @ LHC Conference 2012 Niels Bohr International Academy and Discovery Center, Copenhagen 12 April 2012. Introduction.

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Higgs decays to fermions in CMS (H  , H bb, a )

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  1. Higgs decays to fermions in CMS (H  , Hbb, a) Rainer Mankel Deutsches Elektronen Synchrotron (DESY) for the CMS Collaboration Standard Model @ LHC Conference 2012 Niels Bohr International Academy and Discovery Center, Copenhagen 12 April 2012

  2. Introduction • Standard model (SM) has been extremely successful in describing wide range of phenomena in particle physics • only remaining undiscovered SM particle: Higgs boson • comprehensive approach covering many different production mechanisms & decay channels • Di-fermion final states: • below the thresholds for di-boson (W, Z) production,  lepton and b quark offer relatively large masses for the Higgs to couple to • play important rôle in low-mass region • Beyond a discovery, an essential goal is to investigate the detailed structure of the Higgs sector • di-fermion decays are an important probe distinguishing different structural options R. Mankel; Higgs decays to fermions in CMS

  3. SM Higgs Production & Decays W/Z associated gg fusion VBF • For a Standard Model Higgs, di-fermion decay modes dominate for mH<130 GeV R. Mankel; Higgs decays to fermions in CMS

  4. Higgs Sector: Structure? ? R. Mankel; Higgs decays to fermions in CMS

  5. Structure of the Higgs Sector H bb,  _ • MSSM (=minimal supersymmetric extension) • two complex Higgs doublets • physical states: h, H, A, H  (mA, tan ) • avoids quadratic divergences • new mass scale parameter  “ term problem”   “” • NMSSM (=next to minimal supersymmetric extension) • avoids “ term problem” • two complex Higgs doublets + additional singlet field • physical states are mixtures: h1, h2, h3, a1, a2, H a  CP-even CP-odd • Standard Model • one physical Higgs state (H) • quadratically divergent self-energy corrections at high energies R. Mankel; Higgs decays to fermions in CMS

  6. _ R. Mankel; Higgs decays to fermions in CMS H  bb Searches

  7. VHV(bb) _ _ - • For a light standard model Higgs, Hbb would be the predominant decay channel • observation of Hbb decay is essential to determine nature of Higgs • For ggH (~17pb for mH=120 GeV), QCD background is overwhelming • relation improves in association with W or Z boson  boosted analysis. • Five final states considered: • W(e)H, W()H • Z(ee)H, Z()H, Z()H • Main backgrounds: • Z/W + jets, t+X, tt, VV, QCD multi-jet • background contributions normalized in control regions • mass-based and boosted decision tree-based (BDT) analyses R. Mankel; Higgs decays to fermions in CMS

  8. VH(bb) Analysis (cont’d) • (arXiv:1202.4195, submitted to P.L. B) • Mass-based cut & count analysis • pT(W)>160 GeV • pT(Zll)>100 GeV • ETmiss>160 GeV for Z( )H • ETmiss>35 GeV for W(e)H • Combined Secondary Vertex (CSV) algorithm used for b tagging • combines impact parameter and secondary vertex information in a discriminant • No signal observed R. Mankel; Higgs decays to fermions in CMS

  9. BDT Output (Selected Channels) for mH=115 GeV • Boosted decision tree technique used to improve separation of signal & background • Variables for selection & training: • For various variables relaxed selection cuts • BDT increases sensitivity by ~10% in each channel R. Mankel; Higgs decays to fermions in CMS

  10. VHV(bb): Results BDT analysis No significant signal observed in any of the channels Total expected limit ~ 3x SM expectation (mH=115 GeV) Observed limit from combination consistent with expectation BDT analysis (lower plot) performs 2-20% better than the mass-spectrum-based analysis (upper) R. Mankel; Higgs decays to fermions in CMS

  11. H   Searches R. Mankel; Higgs decays to fermions in CMS

  12. H    _ • (arXiv:1202.4083, submitted to P.L. B)  had New! e had e  CMS PAS HIG-12-007   e e had had Vector Boson Fusion Inclusive Boosted Little sensitivity due to background R. Mankel; Higgs decays to fermions in CMS At lowest masses 2nd strongest decay mode after Hbb Final states: Standard Model search: event categories by production mechanisms:

  13. H    (cont’d) H VBF category • m() estimated by kinematic maximum likelihood fit • effective resolution ~21% • Irreducible background from Z  • addressed with “embedding method” • in Z events from real data, the ’s are replaced by simulated ’s • New: H • very challenging channel • irreducible background from Z  • addressed by evaluating the distance of closest approach between ’s • signal enhancement with likelihood method R. Mankel; Higgs decays to fermions in CMS

  14. H    (cont’d) H    [e ,e had,  had] H    • No significant excess over the expected standard model background contributions is observed • Combination e ,e had,  had : • expected & observed 95% CL limit ~ 3x SM expectation (mH=115 GeV) • observed limit consistent • Addition of H  channel improves on combined limit from the other three decay • combination result in preparation R. Mankel; Higgs decays to fermions in CMS

  15.  MSSM Search b-Tag: Non b-Tag: b Non b-Tag: b-Tag:   • Mainly two processes contribute to pp+X • Subsample with one btaggedjet has increased sensitivityfor MSSM Higgs boson search • smaller relative contribution from inclusive Z production R. Mankel; Higgs decays to fermions in CMS

  16.  MSSM Search H    [He ,e had,  had] • Excludes previously unexplored territory • 95% CL exclusion range for tan  extends down to 7.1 at mA~160 GeV • narrowed parameter space at low mA •   channel alone fairly competitive with other measurements R. Mankel; Higgs decays to fermions in CMS

  17. a   Search R. Mankel; Higgs decays to fermions in CMS

  18. Search for a CMS PAS HIG-12-004 (HIGLU) • In the NMSSM, one of the two CP-odd scalars could be very light • superposition of CP-odd doublet scalar and the additional singlet scalar  mixing angle A • even m(a)<2 mB thinkable • sensitive to Cabb coupling • Consider here: 5.5 <ma< 8.8 GeV, 11.5 <ma< 14 GeV • up to now, strongest constraints come from BaBar through (3S)a • Cross section could be large R. Mankel; Higgs decays to fermions in CMS

  19. a (cont’d) • Di-muon mass spectrum in  mass region • Main backgrounds: • Upsilon resonances  exclude mass region of 9-11 GeV • QCD continuum R. Mankel; Higgs decays to fermions in CMS

  20. a (cont’d) Range 1 Range 2 Range 1 Range 2 Mass scan with Gaussian signal PDF Accounting for radiative tail of (1S) in range 1 R. Mankel; Higgs decays to fermions in CMS

  21. a (cont’d) Range 1 Range 2 • Improvements on BaBar limits for NMSSM parameter |cos A| in lower mass range • CDF published limits relative to (1S) cross section (not shown) • No BaBar or CDF limits in upper mass region R. Mankel; Higgs decays to fermions in CMS

  22. Di-Fermion Channels in SM Combination R. Mankel; Higgs decays to fermions in CMS

  23. SM Higgs Searches: Comparison Di-Fermion with Other Channels • (arXiv:1202.1488, submitted to P.L. B) • Di-fermion channels show very good consistency with the di-boson channels • At mH=125 GeV, consistently see mild excess at level expected by standard model R. Mankel; Higgs decays to fermions in CMS

  24. CMS SM Higgs Searches Combined • Showing low-mass region, where di-fermion decays contribute most • HWW dominates in 125-200 GeV (HZZ beyond) • H dominates below 120 GeV • Excluded mass ranges @ 95% CL: • expected 114.5-600 GeV • observed 127.5-600 GeV • More data are required to assess nature of observed excess R. Mankel; Higgs decays to fermions in CMS

  25. Summary _ • More CMS results in fermion channels (not shown in this talk): • Search for doubly charged Higgs boson CMS PAS HIG-12-005 • Search for WH  e(), () CMS PAS HIG-12-006 • Di-fermion channels particularly important at low Higgs masses • also sensitive to detailed structure of Higgs sector • Standard Model Higgs search: • in bb and  channels, 95% CL limits at low mass range near 3x SM • recent improvement due to  channel • MSSM search: •  channel excludes wide area in (mA, tan ) parameter space • NMSSM search: • upper limits for very light pseudoscalar Higgs boson ( channel) • Excellent prospects for 2012 LHC run (just started…) R. Mankel; Higgs decays to fermions in CMS

  26. Further information R. Mankel; Higgs decays to fermions in CMS

  27. SM Higgs Combination R. Mankel; Higgs decays to fermions in CMS Observed and expected 95% CL confidence limits on the signal strength parameter = / SM for the SM Higgs boson hypothesis

  28. SM Higgs Combination Observed and expected 95% CL confidence limits on the signal strength parameter =/ SM for the SM Higgs boson hypothesis by decay channel R. Mankel; Higgs decays to fermions in CMS

  29. SM Higgs Combination ^ Observed local p-value (p0) and best-fit =/ SM R. Mankel; Higgs decays to fermions in CMS

  30. VHV(bb): Example Control Regions _ [unboosted] _ [dilepton mass sideband] [fake MET] • Background-enhanced distributions • Wbb enhanced for WH (top) • V+udscg enhanced for Z()H (bottom, left) • tt enhanced for Z()H (bottom, right) R. Mankel; Higgs decays to fermions in CMS

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