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Search for H g WW (*) at DØ

Search for H g WW (*) at DØ. presented by Per Jonsson Imperial College London On behalf of the D Ø Collaboration. 2004 Phenomenology Symposium University of Wisconsin, Madison, April 26-28 2004. Standard Model Higgs Production @ the Tevatron.

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Search for H g WW (*) at DØ

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  1. Search for HgWW(*)at DØ presented by Per Jonsson Imperial College London On behalf of the DØCollaboration 2004 Phenomenology Symposium University of Wisconsin, Madison, April 26-28 2004

  2. Standard Model Higgs Production @ the Tevatron • Production cross sections are small 1 - 0.1 pb depending on MH • Gluon fusion, gg->H, dominates • Light Higgs preferred by global fit • MH < 251 GeV at 95% C.L. • LEP limit from direct searches • MH > 114.4 GeV at 95% C.L. Per Jonsson Imperial College London

  3. Standard Model Higgs Decay Modes Why look for H->WW(*)? • H->bb is dominant for MH < 135 GeV • Strong interaction background overwhelm signatures with jets • WW branching fraction ~5% for low mass • Main search channel for MH > 120 GeV • Look for the “clean” final states: emnn, eenn and mmnn Per Jonsson Imperial College London

  4. Cross Section Enhancement from Extra Generations E. Arik et al, SN-ATLAS-2001-006 • Extra quark generations could increase production cross section significantly, • Enhancement factor depends on Higgs and quark masses, • A factor of 8.5 is expected for a 4th generation, m4=320 GeV. Per Jonsson Imperial College London

  5. Suppressed Couplings to b,t L. Brucher, R. Santos, hep-ph/9907434 Occurs Beyond the SM in Top Color or Fermiophobic Higgs models, see talk by A. Melnitchouk Increased H->WW(*) branching Per Jonsson Imperial College London

  6. The Upgraded DØ Detector • Completely new tracking system uses 2T magnetic field • Inner Si vertex detector (SMT) provides b-tagging capability • Excellent Run I calorimetry exploited in Run II • Upgraded 3-tier trigger and data acquisition system Per Jonsson Imperial College London

  7. Data Samples • Search for H->WW(*) in the 3 leptonic channels: eenn, emnn and mmnn • Data investigated correspond to integrated lumi. of ~ 180 (ee), 160 (em) and 150 (mm) pb-1 Collected between April 02 and September 03 • MC generated with Pythia passed through detailed detector simulation • Rates normalized to NLO cross section values Per Jonsson Imperial College London

  8. e+ n W+ n W- e- Event Signature-Spin Correlations • Higgs Mass reconstruction not possible due to two neutrinos: Missing ET • Use spin correlations to suppress background. The charged leptons tend to be collinear: Small opening angle Experimental signature: high pT l, small Dfll and large Missing ET Per Jonsson Imperial College London

  9. Azimuthal Opening Angle: Dfll An example: e+e- final state MC Main background Per Jonsson Imperial College London

  10. Missing ET An example: e+e- final state MC Main background Per Jonsson Imperial College London

  11. Event Selection Event selection includes: • Require two oppositely charged isolated leptons l = e, m • ee: pT(e1) > 12 GeV, pT(e2) > 8 GeV • em: pT(e) > 12 GeV, pT(m) > 8 GeV • mm: pT(m1) > 20 GeV, pT(m2) > 10 GeV • Missing ET greater than: 20 GeV (ee,em); 30 GeV (mm) • Removal of mass resonances: • 12 GeV < m(e,e) < 80 GeV • m(m,m)> 20 GeV and |m(m,m)- mZ| > 15 GeV • Azimuthal opening angle: Df(e,e) < 1.5; Df(e/m,m) < 2.0 • Rejection of energetic jets: • ee, em : E T1< 90 GeV or ET1 < 50 GeV, ET2 < 30 GeV • mm: ET1 < 60 GeV, ET2 < 30 GeV Signal acceptance is ~ 0.02 – 0.2 depending on the Higgs mass/final state Per Jonsson Imperial College London

  12. Invariant mass: mee and mmm Data vs. MC after preselection Higgs of 160 GeV Per Jonsson Imperial College London

  13. Missing ET Data vs. MC after preselection DØ Run II Preliminary mm ee Higgs of 160 GeV Per Jonsson Imperial College London

  14. Opening Angle:Df(e,e) After final selection Afterpreselection Higgs of 160 GeV Per Jonsson Imperial College London

  15. Opening Angle: Df(e,m) After preselection After final cut Good agreement between data and MC in all final states and variables examined Per Jonsson Imperial College London

  16. Event Counts D0 Run II Preliminary Data in agreement with background expectations Per Jonsson Imperial College London

  17. Limits Combined Upper Limits on sxBR between 6-40 pb Excluded cross section times Branching Ratio at 95% C.L. Per Jonsson Imperial College London

  18. Summary • DØ has searched for H->WW(*) with ee, em and mm + MET signatures in 147-177 pb-1 of Run II data • There are a total of 9 events with a background of 11.1 • Cross section limits for the combination of all channels have been calculated • With L= ~1 fb-1 we will start to be sensitive to enhanced Higgs signals • With L= ~ 10 fb-1 we will be sensitive to SM Higgs with MH=160 GeV Looking forward to more data! Per Jonsson Imperial College London

  19. FY’04 Integrated Luminosity Measured luminosity Integrated Luminosity (fb-1) 11/23/03 1/18/04 3/14/04 12 pb-1 / week is also above the design projection design: challenging base: conservative 36×36 bunches 396 ns bunch crossing Start of Fiscal Year Tevatron: Current and Projected Performance Per Jonsson Imperial College London

  20. Higgs Sensitivity Reach Per Jonsson Imperial College London

  21. Back-up Slides

  22. Opening Angle: Df(m,m) After preselection After final cut Per Jonsson Imperial College London

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