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D Ø Higgs Physics Results

D Ø Higgs Physics Results. Jyothsna Rani Tata Institute of Fundamental Research Mumbai, India on behalf of the D Ø Collaboration Lake Louise Winter Institute 20 th – 26 th February 2005 Alberta, Canada. Outline. Standard Model Higgs searches Associated production of H with W

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D Ø Higgs Physics Results

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  1. DØ Higgs Physics Results Jyothsna Rani Tata Institute of Fundamental Research Mumbai, India on behalf of the DØ Collaboration Lake Louise Winter Institute 20th – 26th February 2005 Alberta, Canada

  2. Outline • Standard Model Higgs searches • Associated production of H with W • H  W W* for mH > 135 GeV • Non Standard Model Higgs searches • MSSM Neutral Higgs in (b)bh(b)bbb final state NEW Results presented here are based on 174 – 260 pb-1 Jyothsna Rani - Tata Institute

  3. Missing Piece in Standard Model • The mass of elementary particles in the Standard Model is explained by the presence of Higgs boson. • The mass of the Higgs boson is not predicted in SM. • Precision measurements constrain: 114 GeV < mH < 260 GeV • Tevatron provides: • Indirect search • Precision mt and mw measurements • Direct searches • SM Higgs • non-SM Higgs LEP Jyothsna Rani - Tata Institute

  4. SM Higgs Decays • Search strategies are a function of • Decay modes and • Production channels • Two search strategies at Tevatron: • Low mass Higgs searches mH < 135 GeV H  bb • High mass Higgs searches mH > 135 GeV H  W W* Excluded at LEP Higgs Mass (GeV/c2) Jyothsna Rani - Tata Institute

  5. SM Higgs Production at Tevatron Gluon Fusion: gg  H ~ 1pb At low mass (H  bb), high QCD background. At High mass usable with H W W* decay mode. Associated Production: WH or ZH ~ 0.1pb Used at low mass with H  bb decay mode. Excluded at LEP Jyothsna Rani - Tata Institute

  6. Secondary Vertex Lxy Primary Vertex do Identifying b-jets Performance of Secondary Vertex Tagging algorithm • Secondary Vertex. • Large Impact Parameter of the tracks. Tagging the b-jets is important for H  bb decay modes. Jyothsna Rani - Tata Institute

  7. SM Higgs Search: WH  ln bb • Search Strategy: • Use sample of W(e)+2 b-tagged jets. • Require exactly 2 jets to suppress top background. • 4.4  1.2 events expected and 6 events observed. • (WH)*BR(H bb ) < 9.0 pb @ 95% C.L. for mH =115 GeV • Also (Wbb ) < 6.6 pb @ 95% C.L. for pT(b) > 20 GeV 115 GeV Jyothsna Rani - Tata Institute

  8. e+ n W+ n W- e- SM Higgs Search: H  WW  ln ln • Search strategy: • 2 high pT leptons and MET • WW comes from spin 0 Higgs: • leptons prefer to point in the • same direction  * BR(H→WW) < 5.7pb @ 95% C.L. for mH=160 GeV Jyothsna Rani - Tata Institute

  9. Higgs in Minimal Supersymmetry • MSSM has pairs of Higgs doublet fields • Hu couples to up-type quarks and leptons and Hdto down-type • tan  = <Hu>/<Hd> • 5 Higgs particles after EWSB: h0, H0, A0, H+, H- • h0 is predicted to be light: m h0 < ~ 130 GeV (MSSM) ~ tan  h0, H0, A0 production @ Tevatron Z+b Probe of b-quark PDF  bh and single top production (Z+b) / (Z+j) = 0.023  0.005 (DØ – hep-ex/0410078) = 0.018  0.004(CTEQ6 prediction) Jyothsna Rani - Tata Institute

  10. Higgs Production and Large tan  • Large tan→enhancedbbh/H/A • At tree level , cross section rises like tan2 • A and h/H are produced simultaneously. Total cross section A h CP odd Higgs CP even Higgs H Jyothsna Rani - Tata Institute

  11. Analysis Overview • Signal: • at least 3 b-tagged jets • Invariant mass of two leading • pTjets • Backgrounds: • “QCD heavy flavor” : bbjj, ccjj, cccc, bbcc, bbbb • “QCD fakes” : jjjj • “Other” : Z(bb,cc),tt • Kinematic cuts • Cut on pT of leading jets • (Optimized for each Higgs mass) • Search for an excess of events • in di-jet invariant mass distribution • consistent with a Higgs signal • shape. Di-jet invariant mass in  3b-tagged events 260 pb-1 Jyothsna Rani - Tata Institute

  12. NEW (b)bh Limits on  and tan 260 pb-1 260 pb-1 Two benchmark scenariosMax Mixing: Xt = At - cot = 6;No Mixing: Xt = 0 For mA = 120 GeV < 31 pb-1 @ 95% C.L. and tan< 55 @ 95% C.L.(Max Mixing) Jyothsna Rani - Tata Institute

  13. Summary • Higgs hunting at Tevatron is ongoing. • SM Higgs searches: • DØ placed limits on cross section on WH( bb). • (Z+b) / (Z+j) ratio has been measured. • Understanding of backgrounds is improving. • H  W W*searches placed limits on cross section. • Non SM Higgs searches: • Enhanced Higgs production at high tan is used to exclude (mA, tan) plane. • Expect substantial improvements in Higgs hunting with ~0.6 fb-1 already on tapes. Jyothsna Rani - Tata Institute

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