1 / 33

Higgs Searches at Tevatron Stéphanie Beauceron LPNHE - Paris

Higgs Searches at Tevatron Stéphanie Beauceron LPNHE - Paris on behalf of CDF and DØ Collaborations. Thanks to everybody for their contribution to this talk. Outline. Chicago .  p. p. 1.96 TeV. Booster. p. CDF. DØ. Tevatron.  p. p sou rce. Main Injector & Recycler.

lorin
Download Presentation

Higgs Searches at Tevatron Stéphanie Beauceron LPNHE - Paris

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Higgs Searches at Tevatron Stéphanie Beauceron LPNHE - Paris on behalf of CDF and DØ Collaborations Thanks to everybody for their contribution to this talk Stephanie Beauceron - LPNHE Paris VI et VII

  2. Outline Chicago  p p 1.96 TeV Booster p CDF DØ Tevatron p p source Main Injector & Recycler • Standard Model Higgs • Higgs Beyond the Standard Model • limits on Wbb/WH production • (Z+b)/(Z+j) ratio • limits on HWW(*)l+l- production • limits on neutral Higgs at high tanβ • limits on Non-SM h production • limits on H++/H-- • Summary 36×36 bunches 396 ns bunch crossing Stephanie Beauceron - LPNHE Paris VI et VII

  3. Tevatron: current and projected performance 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 Stephanie Beauceron - LPNHE Paris VI et VII

  4. Standard Model Higgs H bb H  WW(*) Dominant decay modes • Production cross sections are small 0.1 - 1 pb depending on MH • MH 135 GeV gg  H  bb dominated by QCD background  searches can be performed inW/Z associatedproduction to handle backgrounds • MH >135 GeV gg  H WW(*)l+l- final states can be explored at higher masses Production Cross section Stephanie Beauceron - LPNHE Paris VI et VII

  5. New EW constraint Constraint mH in the Standard Model Old Top mass combination New Top mass combination using new DØ run I measurement Direct searches at LEP2: mH>114.4 GeV @95%CL Stephanie Beauceron - LPNHE Paris VI et VII

  6. Higgs Beyond the Standard Model • MSSM • 5 physical Higgs: • 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: • One higgs mass • Other Possibilities • Left-Right Symmetric, Little Higgs, Higgs Triplet models: Doubly Charged Higgs • SM extensions that suppress fermion couplings • Fermiophobic Higgs • TopColor Higgs MSSM Higgs Production Cross section Large enhancement of rates over HSMbb MSSM Higgs Main Decay h/H/Abb ~ 90% h/H/A ~ 10% H+ ~ 100% (tan>1)

  7. b-jet tagging DØ RunII Preliminary • DØ in Run II is able to b-tag up to |η| < 2.5 • Performance being improved • Essential for Hbb searches • Can make use of the track impact parameter (IP) measurements or secondary vertex reconstruction • CDF:performance of sec. vtx. algorithm (after kinematics cuts) • ~50% b-tagefficiency for~0.6%light quarkmis-tagrate in|η| < 1 b-tagging efficiency vs light quark mis-tag rate Both experiments are demonstrating good b-tagging capabilities Stephanie Beauceron - LPNHE Paris VI et VII

  8. DØ: W(en)bb production (1) Motivation: Background to WH production Event selection Central isolatede, 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 plus Pythia through detailed detector response • Cross sections normalized to MCFM NLO calculations Good understanding of data Stephanie Beauceron - LPNHE Paris VI et VII

  9. DØ: W(en)bb production (2) Observe8, expect8.3±2.2 Bkgd. dominated by top evts. At least two b-tags One b-tag Require jets to be tagged, consistent result with different b-tagging algorithms Good agreement between data and MC in both cases Stephanie Beauceron - LPNHE Paris VI et VII

  10. DØ: W(en)bb production (3) • W Transverse mass of 2 Tagged events, keep event with 25 GeV<MT(W)<125 GeV We observed 5 events, expect 6.9  1.8 events Set limits on production of (Wbb) < 20.3 pbat 95% C.L. Stephanie Beauceron - LPNHE Paris VI et VII

  11. DØ: W(en)bb production (4) • Optimize Wbb signal by suppressing the top production by requiring exactly two jets • Observe2 evts., expect2.5±0.5 • Sample composition • Requiring all jets to be b-tag by the 3 b-tagging algorithms of DØ to reduce the background •  Observe 2 evts., expect 0.3±0.1 (Bckd) + 0.6±0.2 Wbb (Signal) Probability(B)=0.04 ; Probability(S+B)=0.23 Standard Model without Wbb disfavored at 2  level Stephanie Beauceron - LPNHE Paris VI et VII

  12. 3 views of high dijet mass (220 GeV) Wbb (WH) candidate Vertex view of 2nd candidate dijet mass (48 GeV) ETmiss

  13. DØ: W(en) H(bb) production Observe2 evts., expect2.5±0.5 In Mass windows [85-135] we observe: 0 events0.54 ± 0.14 expect background0.03 ± 0.01 WH Systematics studies: Set limits on production of(WH)B(Hbb) < 12.4 pb for MH = 115 GeV at 95% C.L. Stephanie Beauceron - LPNHE Paris VI et VII

  14. CDF: W(en/mn)H(bb) production (1) Event selection Central isolatede/, pT > 20 GeV Missing ET> 20 GeV Two jets:ET > 15 GeV, || < 2 Veto Di-lepton, extra jet  Observe 2072 events in data in Lint=162 pb-1 Simulations performed with Alpgen plus Herwig passed through detailed detector response Good agreement between data and MC Stephanie Beauceron - LPNHE Paris VI et VII

  15. CDF: W(en/mn)H(bb) production (2) Enrich the b-content of events Require at least one b-tagged jet  Observe 62 events in data  Expect 61 ± 5 events Main contributions to the bkgd: Expect0.3 evtsfrom Higgs Signal acceptance of ~ 1.8% for MH = 110 – 130 GeV good agreement between data and MC Stephanie Beauceron - LPNHE Paris VI et VII

  16. CDF: W(en/mn)H(bb) production (3) Set limits on the Higgs production cross section times branching fraction at 95% C.L. : ×B < 5 pb Systematics studies Exceeds CDF’s Run I limit[PRL 79, 3819(1997)] ×B < 14 – 19 pb forMH = 70 – 120 GeV Stephanie Beauceron - LPNHE Paris VI et VII

  17. Motivation Background to ZH production Probes PDF of the b-quark LO diagrams for ZQ Measure cross section ratio (Z+b)/(Z+j) Many uncertainties cancel DØ: Z(ee/mm)b production (1) • Data correspond to integrated lumi. of 184 (ee), 152 (mm) pb-1 • Event selection • Isolatede/mwithpT > 15/20 GeV, |h| < 2.5/2.0 • Z peak for signal, side bands for bkgd. evaluations • JetET > 20 GeV, |h| < 2.5 • At leastone 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 Stephanie Beauceron - LPNHE Paris VI et VII

  18. DØ: Z(ee/mm)b production (2) Transverse energy spectrum of b-tagged jets QCD and mistag bkgd. estimated from data MC: Pythia Zb normalized to data Measure cross section ratio Z+b/Z+j 0.024 ± 0.005 (stat) (syst) Theory: ~0.02 hep-ph/0312024 Systematics studies + 0.005 – 0.004 Stephanie Beauceron - LPNHE Paris VI et VII

  19. DØ: H  WW(*)  l+l-nn final states; l=e,m • Event selection • 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)and150 (mm) pb-1 Data vs MC after evt. preselection Stephanie Beauceron - LPNHE Paris VI et VII

  20. DØ: H  WW(*)  l+l-nn final states; l=e, m e+ n W+ n W- e- • Higgs mass reconstruction not possible due to two neutrinos • Employ spin correlations to suppress the bkgd. • Df(ll) variable is particularly useful • Leptons from Higgs tend to be collinear Azimuthal angle between e and m (after event pre-selection) Higgs of 160 GeV Good agreement between data and MC in all final states, and all variables examined so far Stephanie Beauceron - LPNHE Paris VI et VII

  21. DØ: H  WW(*)  l+l-nn final states; l=e, m DØ Run II Preliminary Signal acceptance is ~ 0.02 – 0.2 depending on the Higgs mass/final state • Number of events after selections • Dominant bkgd. in em sample Excluded cross section times Branching Ratio at 95% C.L. Higgs of 160 GeV Stephanie Beauceron - LPNHE Paris VI et VII

  22. DØ: Neutral Higgs Bosons at High Tan in Multi-jets Events (=h,H,A) • 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 BR( ) ~ 90% Dijet Mass (Higgs signal at 95% C.L. exclusion limit) Stephanie Beauceron - LPNHE Paris VI et VII

  23. DØ: Neutral Higgs Bosons at High Tan in Multi-jets Events Signal acceptance is ~ 0.2 – 1.5% depending on the Higgs mass/final state Stephanie Beauceron - LPNHE Paris VI et VII

  24. DØ: Search for Non-SM Light Higgs in H • Data correspond to integrated lumi. of 191 pb-1 • Event selection • 2 IsolatedwithpT > 25 GeV, ||<1.05 (CC) or 1.5<||<2.4 (EC) • pT > 35 GeV • 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) • Dominant uncertainty in background estimation is in the measurement of  mis-ID rate (~30%) Stephanie Beauceron - LPNHE Paris VI et VII

  25. DØ: Search for Non-SM Light Higgs in H • No clear evidence of excess • Perform counting experiments on optimized sliding mass window to set limit on B(H) as function of M(H) Stephanie Beauceron - LPNHE Paris VI et VII

  26. CDF: Search for H++ • H++/H-- predicted in models that contain Higgs triplets • Left-Right (LR) symmetric models • SUSY LR models : low mass (~100 GeV – 1 TeV) • Event selection • 1 pair of same sign ee, or , or ein mass window of 10%*M(H++)(~3 detector resolution) • same sign leptons decay contains low SM backgrounds, provide clean environment for new physics search • Data correspond to integrated lumi. of 240 pb-1

  27. CDF: Search for H++ • Background prediction for M(l+ l+) >80 GeV (>100 GeV for ee) • Data : observe 0 event Stephanie Beauceron - LPNHE Paris VI et VII

  28. Prospectives for Higgs • New study from CDF + DØ : • Improvement of the results with a detailed simulation. Statistical power onlySystematics not included 5sdiscovery 3sevidence 95% CL exclusion Stephanie Beauceron - LPNHE Paris VI et VII

  29. Summary • Hunting for Higgs at the Tevatron Run II has begun ! • Understanding of the background processes to the Higgs production is gradually improving • Result summary: • (Wbb)< 20 pb • (WH) B(Hbb) < 12 pb (We) • (WH) B(Hbb) < 5 pb (We and W) • (Z+b)/ (Z+j) = 0.024 ± 0.005 (stat) (syst) • limits set on (H)B(HWW(*)) • Search for Neutral Higgs in MSSM: • excludes A and h/H for masses 90-150 GeV/c2 at high tan β (>~100) • H++ Search: • Limits 115, 135, 135 GeV/c2 for exclusive HL decays to e, ee,  • Limits 110 GeV/c2 for exclusive HR decays to  • Search for H: • Limits are set for the Branching Ratio vs Mass for both Fermiophobic and TopColor models Already a lot of results and more are coming! + 0.005 – 0.004

  30. The upgraded CDF and DØ detectors • New • silicon detector • drift chamber • TOF PID system • Upgraded • calorimeter, muon system • DAQ/trigger • displaced-vertex trigger • New (tracking in B-field) • silicon detector • fiber tracker • Upgraded • calorimeter, muon system • DAQ/trigger • (displaced-vertex trigger soon) Stephanie Beauceron - LPNHE Paris VI et VII

  31. Run I CDF H+ Search Stephanie Beauceron - LPNHE Paris VI et VII

  32. DØ H++ Search (1) • search assume the H±± decay branching ratio to like-sign muons to be 100%. • Muon ID and analysis requirements • Make data quality requirements based on official good run lists • Select di-muon trigger events • Have muon identification requirements based on: • Track segments reconstructed in the muon system, isolation from signficant energy deposition in the calorimeter and 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 |eta| < 2 Dimuon mass spectra at various steps of the event selection procedure Stephanie Beauceron - LPNHE Paris VI et VII

  33. DØ H++ Search (2) • Search assumes the H±± decay branching ratio to like-sign muons to be 100%. • Confidence level of the signal as a function of the H++ mass,for the left- and right-handed Higgs bosons Stephanie Beauceron - LPNHE Paris VI et VII

More Related