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Higgs Results from D Ø

Higgs Results from D Ø. presented by Per Jonsson Imperial College London On behalf of the D Ø Collaboration. Hadron Collider Physics 2004 Michigan State University, East Lansing, June 14-18, 2004. Introduction Tevatron D Ø detector Higgs production/sensitivity Standard Model Higgs

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Higgs Results from D Ø

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  1. Higgs Results from DØ presented by Per Jonsson Imperial College London On behalf of the DØCollaboration Hadron Collider Physics 2004 Michigan State University, East Lansing, June 14-18, 2004

  2. Introduction Tevatron DØ detector Higgs production/sensitivity Standard Model Higgs Limits on Wbb/WH s(Z+b)/s(Z+j) ratio HgWW(*)gl+l-nn searches Higgs Beyond the Standard Model Limits on neutral SUSY Higgs at high tanb Limits on non-SM hggg production Limits on H++/H-- Summary Chicago  p p 1.96 TeV Booster p CDF DØ Tevatron p p source Main Injector & Recycler Outline 36×36 bunches 396 ns bunch crossing Thanks to all colleagues for their contribution to these studies Per Jonsson - Imperial College London

  3. Tevatron Performance(1) Per Jonsson - Imperial College London

  4. FY’04 Integrated Luminosity Measured luminosity Integrated Luminosity (fb-1) 11/23/03 1/18/04 3/14/04 12 pb-1 / week is above the design projection design: challenging base: conservative 36×36 bunches 396 ns bunch crossing Start of Fiscal Year Tevatron Performance (2) FY 04 integrated lumi 11/23/03 05/09/04 Per Jonsson - Imperial College London

  5. New (tracking in B-field) silicon detector fiber tracker Upgraded calorimeter, muon system DAQ/trigger The upgraded DØ detector Needed for Higgs searches! Per Jonsson - Imperial College London

  6. EW constraints on Higgs Old Top mass combination: MH constrained in the Standard Model New Top mass combination using new DØ Run I measurement: Direct searches at LEP2: MH>114.4 GeV @95%CL Per Jonsson - Imperial College London

  7. Production cross sections are small: 0.1-1 pb depending on MH MH< 135 GeV: decay to bb gg gH gbb overwhelmed by QCD background searches can be performed in W/Z associated production with lower background Best channels: WHglnbb, ZHgnnbb MH > 135 GeV: decay to WW gg gH gWW(*)gl+l-nn final states can be explored clean, but small branching H bb H  WW(*) Dominant decay modes SM Higgs Production We may have Higgs in our data already! Per Jonsson - Imperial College London

  8. No systematics SM Higgs Sensitivity • New Higgs sensitivity study from CDF + DØ in 2003: Statistical power onlySystematics not included Improved sensitivity from refined analysis and detailed simulation The SM Higgs is a challenge, understanding of bkgs critical! Per Jonsson - Imperial College London

  9. Larger cross sections and/or cleaner search topologies MSSM 5 physical Higgses: Two CP-even scalars: h (lighter, SM-like) H (heavier) CP-odd scalar: A Charged Higgs pair: H± At tree-level, two free parameters: Ratio of vacuum expectation values: tanb = nu/nd One Higgs mass: mA Other possibilities: Left-Right Symmetric, Higgs Triplet models: Doubly Charged Higgs SM extensions which suppress fermion couplings Fermio-phobic or TopColor Higgs Higgs Beyond the Standard Model Enhanced s over HSMbb (prop. to tan2b) MSSM Higgs Main Decays h/H/Abb ~ 90% h/H/A ~ 10% H+ ~ 100% (tan>1) Per Jonsson - Imperial College London

  10. demonstrated good b-tagging capability up to |h|<2.5 Essential for Hgbb searches New for DØ in Run II DØ RunII Preliminary B-jet tagging b-tagging efficiency vs light quark mis-tag rate • Use track impact parameter • (IP) measurements or secondary • vertex reconstruction • Several algorithms available Performance being improved Per Jonsson - Imperial College London

  11. Motivation: Background to WH production Event selection includes: Central isolated e, pT > 20 GeV Missing ET> 25 GeV ≥ two jets:ET > 20 GeV, |η| < 2.5 2587 evts. in Lint=174 pb-1 of data Simulations with Alpgen and Pythia through detailed detector response Cross sections normalized to MCFM NLO calculations W(gen)bb production (1) Good understanding of data Per Jonsson - Imperial College London

  12. Require jets to be b-tagged: use different b-tag algorithms consistent results with all Observe 8, expect 8.3±2.2 Background dominated by top events At least two b-tags At least one b-tag W(gen)bb production(2) Good agreement between data and MC in both cases Per Jonsson - Imperial College London

  13. Exactly two jets: suppress top production Observe 2 events, expect 2.5±0.5 Sample composition: W(gen)bb production (3) Set limit on production of: s(Wbb) < 20.3 pb (WH)xBr(Hbb) < 12.4 pb for MH = 115 GeV at 95% C.L. Systematics studies for Wbb: (Systematics smaller for WH) Per Jonsson - Imperial College London

  14. Motivation: Background to ZH production Benchmark for SUSY Higgs production via gbbh Probes PDF of the b-quark Examples of ZQ (Zj) LO diagrams: Data correspond to integrated luminosity of 184 (ee), 152 (mm) pb-1 Event selection includes: Isolated e/m with pT > 15/20 GeV,|h| < 2.5/2.0 Z peak for signal, side bands for background evaluation Jet ET > 20 GeV, |h| < 2.5 At least one b-tagged jet Simulations performed with Pythia or Alpgen plus Pythia passed through detailed detector response Cross sections normalized to data Relative b- and c-quark content as given by MCFM NLO calculations Z(gee/mm)b associated production (1) • Measure cross section ratio: • (Z+b)/(Z+j) • Many uncertainties cancel Per Jonsson - Imperial College London

  15. Transverse energy spectrum of b-tagged jets QCD and mistag background estimated from data MC: Pythia Zb normalized to data Measured cross section ratio Z+b/Z+j: 0.024 ± 0.005 (stat) (syst) Theory: ~0.02hep-ph/031202 Systematics studies: Z(gee/mm)b production (2) + 0.005 –0.004 Per Jonsson - Imperial College London

  16. Event selection includes: Isolated e/m pT(e1) > 12 GeV, pT(e2) > 8 GeV pT(e/m1) > 12 GeV, pT(e/m2) > 8 GeV pT(m1) > 20 GeV, pT(m2) > 10 GeV Missing ET greater than 20 GeV (ee, em); 30 GeV (mm) Veto on Z resonance Energetic jets Simulations done with Pythia passed through detailed detector response Rates normalized to NLO cross section values Data correspond to integrated lumi. of ~ 180 (ee), 160 (em) and 150 (mm) pb-1 HgWW(*)gl+l-nn (l=e,m)(1) Data vs MC after preselection Per Jonsson - Imperial College London

  17. Higgs mass reconstruction not possible due to two neutrinos Employ spin correlations to suppress the background Df(ll) variable is particularly useful e+ n W+ n W- e- HgWW(*)gl+l-nn (l=e,m )(2) Azimuthal angle between e and m (after event pre-selection) • Charged leptons from Higgs are collinear Higgs of 160 GeV Good agreement between data and MC Per Jonsson - Imperial College London

  18. Signal acceptance is ~ 0.02 – 0.2 depending on the Higgs mass/final state Number of events after selection DØ Run II Preliminary HgWW(*)gl+l-nn (l=e,m)(3) Excluded cross section times Branching Ratio at 95% C.L. • Dominant Background in em sample Higgs of 160 GeV Per Jonsson - Imperial College London

  19. Event Selection: Multi-jet data sample At least 3 jets:ET cuts on jets are optimized separately for different Higgs mass points, and for min. # jets required in the event  3 b-tagged jets Look for signal in the invariant mass spectrum from the two leading b-tagged jets Simulations performed with Pythia or Alpgen plus Pythia passed through detailed detector response Data correspond to integrated lumi. of 131pb-1 Neutral Higgs Bosons at High tanb in Multi-jet Events (=h,H,A) BR( ) ~ 90% Dijet Mass (Higgs signal at 95% C.L. exclusion limit) Per Jonsson - Imperial College London

  20. Neutral Higgs Bosons at High tanb in Multi-jet Events Signal acceptance is ~ 0.2 – 1.5% depending on the Higgs mass/# of jets Per Jonsson - Imperial College London

  21. Small in the SM Some extensions of SM contain Higgs w/ large B(h) Fermiophobic Higgs : does not couple to fermions Topcolor Higgs : couple to top (only non-zero fermion coupling) Data correspond to integrated lumi. of 191 pb-1 Event selection: 2 Isolated with pT > 25 GeV, ||<1.05 (CC) or 1.5<||<2.4 (EC) pT > 35 GeV Search for Non-SM Light Higgs in hggg • Dominant uncertainty in background • estimation is the measurement of  • mis-ID rate (~30%) Per Jonsson - Imperial College London

  22. Search for Non-SM Light Higgs in hggg • No clear evidence of excess • Perform counting experiments on optimized sliding mass window to set limit on B(h) as function of Mh Per Jonsson - Imperial College London

  23. H++/H-- appear in LR symmetric and Higgs triplet models: Leading order pair-production: qqgZ/g*gH++H— Dominant decay mode: like-signed leptons Same sign muon decays contain low SM background: clean environment for new physics search Select di-muon triggered events muon identification requirements: Isolated muons with an associated track from the central tracking system. The muon momentum is taken as the central track momentum Muons are required to have PT > 15 GeV and |h| < 2 Di-muon mass spectra at various steps of the event selection procedure H++/H-- Search(1) Per Jonsson - Imperial College London

  24. H++/H-- Search (2) • 2 candidates in L=107 pb-1, expected bkg of 0.34 from SM • Search assumes the H±± branching ratio to like-sign muons to be 100% • Confidence level of the signal as a function of the H±± mass, for left- and right-handed Higgs bosons MH> 116 GeV MH> 95 GeV DØ Run II prel. DØ Run II prel. Per Jonsson - Imperial College London

  25. Summary • The hunt for Higgs in DØ Run II data is on! • The upgraded DØdetector is producing world class results • Understanding of background processes progressing • Result summary: • (Wbb)< 20 pb • (WH)xBr(Hbb) < 12 pb (We) • (Z+b)/ (Z+j) = 0.024 ± 0.005 (stat) (syst) • limits set on (H)xBr(HWW(*)) • Search for Neutral Higgs in MSSM: • excludes A/h/H for masses 90-150 GeV at high tanβ (>~100) • Search for h: • Limits are set for the Branching Ratio vs Mass for both Fermiophobic and TopColor models • H++ Search: • Lower mass limits of 116 and 95 GeV for HL and HR decays to  • Limits setare unmatched or superior to Run I + 0.005 – 0.004 Many results already and more with increased stats are coming soon! Per Jonsson - Imperial College London

  26. Extra slides… Per Jonsson - Imperial College London

  27. W(gen)bb production (3) • W Transverse mass of 2 tagged events, keep events with 25GeV<MT(W)<125 GeV We observed 5 events, expect 6.9  1.8 events Set limits on production of (Wbb) < 20.3 pb at 95% C.L. Per Jonsson - Imperial College London

  28. Suppress top production by requiring exactly two jets Observe 2 events, expect 2.5±0.5 Sample composition: W(gen)bb production (4) • Requiring each jet to be tagged by all of the • 3 b-tagging algorithms reduces the background: • Observe 2 events, expect 0.3±0.1 (Background) + 0.6±0.2 Wbb (Signal) Probability(B)=0.04; Probability(S+B)=0.23 Standard Model without Wbb disfavored at 2  level Per Jonsson - Imperial College London

  29. Observe 2 events, expect 2.5±0.5 With 85 GeV< Dijet Mass<135 GeV : 0 events 0.54 ± 0.14 expect background 0.03 ± 0.01 WH W(gen)H(gbb) production Systematics studies for Wbb: (Systematics smaller for WH) Set limit on production of (WH)xBr(Hbb) < 12.4 pb for MH = 115 GeV at 95% C.L. Per Jonsson - Imperial College London

  30. Views of high dijet mass (220 GeV) Wbb(WH) candidate Vertex view of the 2nd candidate (48 GeV) ETmiss Per Jonsson - Imperial College London

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