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Search for Higgs Boson in the H → gg Channel at APS-DPF 2003 by Alex Melnitchouk

This presentation by Alex Melnitchouk at the APS-DPF 2003 conference discusses the search for the Higgs boson via the H → gg decay channel, focusing on its production through gluon fusion at the Tevatron. Highlighting challenges in detection due to the small branching fraction and dominance of other decay channels, the talk explores the implications of Fermiophobic and Topcolor Higgs scenarios. Key methodologies for event selection, as well as background processes, are detailed, aiming to establish cross-section limits using DØ data. The effort to enhance analysis sensitivity concludes with insights on event spectra aligning with Standard Model predictions.

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Search for Higgs Boson in the H → gg Channel at APS-DPF 2003 by Alex Melnitchouk

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  1. Search for the Higgs Boson in thehggChannel APS-DPF 2003 Philadelphia Alex MelnitchoukBrown University on behalf of the DØ collaboration Alex Melnitchouk APS-DPF conference - 2003

  2. = 2 TeV (Z) (Z*) Leading SM Higgs Production Processes at Tevatron gluon fusion : cross-section ~ m2  the top-quark loop is dominant Cross-Section, pb 10.0 W/Z associated 1.0 0.1 0.01 80 100 120 140 160 W/Z fusion Higgs Mass, GeV Alex Melnitchouk APS-DPF conference - 2003

  3. hggdecay in the Standard Model • no tree-level Hgg coupling (Higgs is neutral) • diphoton decays happen via W or top-quark loop:  Hgg branching fraction is small: ~ 10-3-10-4 Higgs decays mostly to b-quark and W pairs • however many extensions of the SM predict enhanced gg decay rate of the Higgs Alex Melnitchouk APS-DPF conference - 2003

  4. hggdecays can be enhanced • due to suppressed couplings to •  all fermions (Fermiophobic Higgs)H.E.Haber et al, Nucl. Phys. B161, 493 (1979) • all fermions but top quark (Topcolor Higgs)B.Dobrescu, Phys. Rev. D63, 015004 (2001) • top and bottom quark J.D. Wells, Phys. Rev. D56, 1504 (1997) •  down-type fermions,H. Baer, J.D. Wells, Phys. Rev. D57, 446 (1998) • Enhanced ggrate is also predicted by some models that employLarge Extra DimensionsL. Hall, C.Kolda, Phys. Lett. B459, 213 (1999) • in addition gg decay loop can be enhanced by a contribution from a heavy charged particle coming from new physics Alex Melnitchouk APS-DPF conference - 2003

  5. Examples of Enhancement of hgg decays hggBranching Fraction no couplings to fermions (Fermiophobic Higgs) no couplings to top,bottom quarks no couplings to down-type fermions Standard Model Higgs Mass, GeV S.Mrenna, J.Wells, Phys. Rev. D63, 015006 (2001) in general we should be prepared for any hgg branching fraction ( up to 1.0 ) due to new physics Alex Melnitchouk APS-DPF conference - 2003

  6. hggSearch Strategy Focus on 2 Scenarios • Fermiophobic Higgs (does not couple to fermions) • Production: W/Z associated + W/Z fusion • Main signature with diphotons : gg + 2jets • Current Mass Limits : D0/CDF RunI : 78.5 / 82.0 GeV at 95% CL • LEP :108.3 GeV at 95% CLhep- ex/0212038 (2002) • Topcolor Higgs (of all fermions couples only to top) • Production: all three leading processes • Main signature with diphotons : gg • Remaining models would give similar signal to one of the two scenarios: e.g. no couplings to down-type fermions  topcolor no t,b couplings  fermiophobic; B.Abbot et al. Phys. Rev. Lett. 82, 2244 (1999 ) F.Abe et al. Phys. Rev. D59, 092002 (1999) LEP Current setting limits on Cross-Section  B(gg) Focus : for the Topcolor Higgs assuming SM couplings Alex Melnitchouk APS-DPF conference - 2003

  7. Major Backgrounds : Drell-Yan and QCD • Z/ge+e-with e+e- misidentified as photons e.g. • QCD processesthat in the final state contain : 1. two photons 2. a photonanda hadronic jet misidentified as photon 3. two hadronic jets misidentified as photons e.g. Alex Melnitchouk APS-DPF conference - 2003

  8. Selection of gg Candidate Events • Trigger: di-EM* high pT trigger • Offline:(on both objects) • Kinematic cuts: pT > 25GeV • Acceptance cuts: Central or End Cap Calorimeter up to ||=2.4 • Photon ID: -shower shape consistent with EM* shape (EMfraction, Isolation, H-matrix 2) • - track veto • *EM = Electromagnetic Object (Photon or Electron) Alex Melnitchouk APS-DPF conference - 2003

  9. Invariant Mass and  from Data and Signal MC DØ RunII Preliminary DØ RunII Preliminary Events / 3GeV Central Calorimeter Detectors differ slightly in mass resolution and ID performance Hadronic End-Cap Calori- meter EM look separately at : – both g’s central – both g’s in end-cap – central, end-cap EM Hadronic Alex Melnitchouk APS-DPF conference - 2003

  10. DØ RunII Preliminary Events / 8 GeV DØ RunII Preliminary Events / 8 GeV Events / 8 GeV DØ RunII Preliminary gg Mass Distributions and Event Counts (Ldt=52pb-1) Alex Melnitchouk APS-DPF conference - 2003

  11. Higgs Cross-Section Limits (Assuming B(gg)=1) • Make a counting experiment in the optimized mass resolution dependent sliding mass window G.Landsberg , K.MatchevPhys. Rev. D62, 035004 (2000) DØ RunII Preliminary  Ldt=52pb-1 Experimental Upper Limit @ 95% CL • ApproachingB(gg)-Mh region of interest • To increase sensitivity : need analysis optimization and better understanding of photon misidentification rate Alex Melnitchouk APS-DPF conference - 2003

  12. Conclusions • A Search for the Topcolor Higgs was performed in the inclusive h gg + X channel with 52pb-1 of DØ data collected between September 2002 and January 2003 • Measured gg spectrum is in agreement with the Standard Model background predictions • First attempt to set Cross-Section Limits with DØ RunII gg data has been made • Work on improving sensitivity is in progress • Another search for the Higgs with suppressed fermion couplings at DØ (HWWtalk by Peter Tamburelo tomorrow) • More data is being accumulated • Stay tuned for new results Alex Melnitchouk APS-DPF conference - 2003

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