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Recent Results: Electroweak, QCD, Top, Higgs, and New Physics

This presentation summarizes the recent results from the DØ Collaboration on ElectroWeak, QCD, Top, Higgs, and searches for physics beyond the Standard Model. Topics include the completion of the SM, precision tests, searches for new phenomena, QCD jet cross sections, and measurements on non-SM Higgs decays.

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Recent Results: Electroweak, QCD, Top, Higgs, and New Physics

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  1. Recent Results From For the DØ Collaboration G. Watts (University of Washington) ElectroWeak QCD Top Higgs

  2. Second Half of New Spring Results Presentation Completing the SM s(WHWbb), s(Wbb) s(Zb)/s (Zj), s(HWW*), Single Top Precision Tests of the SM ds/dpT, ds/dMjj, Azimuthal Jet Decorrelations, s(tt) Searches for physics beyond the SM s(Wg), s(Hgg), s(hbb) New Phenomena and B Physics – see talk by A. Nomerotski on March 26th…

  3. Winter Conference Dataset ~170 pb-1 for these analyses All Data Reprocessed by December 2003 with improved reconstruction Thanks to all for the data!

  4. Wg Cross Section Trilinear Gauge Couplings Small in SM Sensitive to new Physics W pT and MWg Signature e or m and n and photon Primary Background e channel: 162.3 pb-1 m channel 82.0 pb-1 W+Jets, jet fakes a g.

  5. Wg Backgrounds Expected Background Event Counts W+Jets • Jet fakes a photon • Determine photon fake rate from data • 0.3% - 0.1 % for 10 GeV to 50 GeV jets leX Lepton + electron with out track + missing ET tt, etc. Use sample of events with good electron and apply tracking efficiency. Zg, t’s MC based

  6. Wg Results s(ppWg lng+X) 19.3 ± 6.7 ± 1.2(lumi) Signal Eff calculated using Baur MC + Pythia First Step… With increased data detailed Wg kinematic studies will be possible

  7. QCD Inclusive Jet and Dijet Cross Sections Reliable Test of NLO Perturbative QCD Jet Evolution, Parton Distribution Functions, new physics at as. Traditional place to search for new physics Quark Compositeness, etc. Run 2 Datasets Jet Energy Scale is largest systematic error Better discrimination of PDFs Look at both Forward and Central Regions Central Region – large transverse energy – most sensitive to new physics and PDFs Forward Region – Less sensitive to new physics, but still sensitive to PDFs

  8. ds/dpT Central Forward Far Forward Central Similar, with larger errors, for other eta regions Stay tuned for improvements to JES

  9. Mjj

  10. The “Biggest” QCD Event

  11. Jet Azimuthal Decorrelations 3 jets in pQCD Leading Order pQCD Jets are back-to-back Df12 = p Df12 < p Df12 is sensitive to jet formation without having to measure 3rd jet directly!

  12. Jet Azimuthal Decorrelations Look at events with 2 jets 1 Measure Dfdijet Compare to a LO & NLO MC LO MC 3 jet production has pole as pT3 -> 0 1 LO MC 3 jet Dfdijet > 2p/3 2 2 Not compatible with a LO description

  13. Jet Azimuthal Decorrelations Further tests of MC Model ISR rate in MC has strong effect on matching as well. Important for tt, H mass, etc. More data, better JES will continue to improve the power of this measurement.

  14. Non SM H  gg SM H gg Branching Ratio is small, 10-3, 10-4. Beyond SM Suppress Higgs Products Fermiphobic or Top Color Higgs BR(H gg) enhanced • Require 2 isolated EM Objects • pT>25 GeV Backgrounds Z/y ee – (data) gg production (MC) QCD w/jets misidentified (data)

  15. Non SM H  gg Look for resonance in Mgg None found, so set limits… Systematic Errors Dominated by Luminosity determination And photon fake rate determination Split the detector by regions according to fake rates

  16. Non SM H  gg (topcolor) Mh (GeV) Analysis improvements possible by making use of CPS, etc. Fermiophobic model from A. G. Akeroyd, Phys Rev. Lett. 368, 89 (1996)

  17. Tagging a B • Top, Higgs contain b-quark jets • Most backgrounds do not • Leptons from B meson • Contain a B meson • Has finite life time • Travels some distance from the vertex before decaying • ~ 1mm • With charm cascade decay, about 4.2 charged tracks Vertex Tagging a B B Impact Parameter (d) Decay Lengh (Lxy) Hard Scatter Impact Parameter Resolution d/s(d) Several algorithms under active development Decay Length Resolution Lxy/s(Lxy)

  18. CSIP Algorithm Per Taggable Jet Rates Measured in Data! Counting Signed Impact Parameter Based on Impact Parameter Significance S(IP) = IP/s(IP) Jet axis Track 40% q I.P Primary vertex 0.5% Requirements to tag a jet: - at least 2 tracks with S(IP) > 3 - or at least 3 tracks with S(IP) > 2 Light Quark Fake Rate

  19. JLIP Algorithm Jet Lifetime Impact Parameter Based on Impact Parameter Significance • Probability distributions • P(Track from PV) • Defined for each class of tracks • # of SMT Hits, pT, etc. 40% Each jet assigned P(light quark) 0.5% Light Quark Fake Rate

  20. SVT Algorithm Secondary Vertex Tagger Reconstruct Vertices using displaced tracks Cut on Decay Length Significance S(Lxy) = Lxy/s(Lxy). 40% 0.5% Z axis

  21. B Tagging Performance on signal tt lepton+jets ~ 56% Single Top (s channel) ~ 52% Wbb ~ 52% Wj ~ 0.3% Combining the Taggers Already studied the correlations Working now on making a combination

  22. Higgs Production at Large tan • Low tan , → Standard Model Higgs • High tan , →enhancedbbH • Cross section rises like tan2 • Substantial improvements in Theory understanding since Run 1 MSSM Use 3 b-tags Backgrounds Include: QCD: bbh, bbjj, bbbb EW/St: Zb, Z, tt ~tan  4 Jet HF MC QCD not well tested: design around its use Look for excess in di-jet mass window Use shoulders to calibrate

  23. Higgs Production at Large tan • Trigger on 3 jets + • ~60% efficiency • 3 Jets In Event • 20, 15, 15 GeV L=130 pb-1 Background shape determined from data Look for Mass Resonance Normalization determined by fitting to region ±1s from expected higgs signal

  24. Results • Set limit using fitted distributions (TLimit) • Will be down at 40 with MA=100 at 1.6 fb-1 • No analysis improvements taken into account! Search for SUSY Higgs at high tan b

  25. Higgs Decays Search strategies are a function of Decay Channel and Production Channel Nominal Mass Reach Spans Two Decay Modes Low Mass Higgs Searches High Mass Higgs Searches Excluded HDECAY MH[GeV/c2]

  26. ZH, WH Higgs Production Gluon Fusion No Good at Low Mass Overwhelmed by QCD background Good at High Mass Associated Production M. Spira; NLO Good at Low Mass

  27. Same final state as WH One of background processes Event selection include Central isolatede, pT > 20 GeV Missing ET > 25 GeV ≥ two jets: ET > 20 GeV, |h| < 2.5 2587 evts. in Lint=174 pb-1 of data Wbb, electron channel Fair understanding of data • Simulations with Alpgen plus Pythia through detailed detector response • Cross sections normalized to MCFM NLO calculations

  28. At least two b-tags At least one b-tag Wbb, B Tagging Observe8, expect8.3±2.2 Top is principle background! Fair agreement Add a MT window cut for the W (25-125 GeV) s(Wbb) < 20.3 pb Prefer Wbb at 2s Observe 5 events, expect 6.9±1.8

  29. 115 GeV Wbb, B Tagging Suppress Top Production Require NJ = 2 Observe2 evts, expect2.5±0.5 Require All Three Tagging Algorithms Observe2 evts, expect0.3±0.1 SM with no Wbb disfavored at 2s level Expect 0.6±0.2 from Wbb

  30. WH Limits Add mass window cut 85-135 GeV/c2 For WH limit use mass window. Expect 0.03 WH, 0.54 from SM backgrounds, observe 0 s(WH)B(Hbb) < 12.4 pb (MH = 115 GeV/c2) @ 95% C.L.

  31. 3 views of high dijet mass (220 GeV) Wbb (WH) candidate Vertex view of 2nd candidate dijet mass (48 GeV) ETmiss

  32. Background to ZH production Benchmark for SUSY Higgs production via gbbh Probes PDF of the b-quark Z(ee/mm)b • Isolatede/m with pT > 15/20 GeV, |h| < 2.5/2.0 • Z peak for signal, side bands for bkgd. evaluations • Jet ET > 20 GeV, |h| < 2.5 • At least one b-tagged jet L=184 (ee), 152 (mm) pb-1 Jet Flavor Content Calculated with MCFM (NLO) b/c Ratio • Measure cross section ratio • s(Z+b)/s(Z+j) • Many uncertainties cancel Background QCD and Z/g

  33. Z(ee/mm)b Tag required QCD and mistag bkgd. estimated from data Zb normalized to data Good Match to MC Clear Indication of Heavy Flavor

  34. Theory J. Campbell, R. K. Ellis, F. Maltoni, S. Willenbrock hep-ph/0312024 R~0.02

  35. High Mass SM Higgs Search H  WW(*)  l+l-nn • Event selection include • 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 L = 180 (ee), 160 (em) and 150 (mm) pb-1 mm Channel

  36. e+ n W+ n W- e- H  WW(*)  l+l-nn Spin Correlations • Df(ll) – Azimuthal Angle Ztt QCD Leptons from Higgs Tend to be collinear Higgs of 160 GeV Can’t reconstruct mass due to presence 2 neutrinos

  37. DØ Run II Preliminary Higgs of 160 GeV H  WW(*)  l+l-nn s X BR 95% CL em Signal acceptance is ~ 0.02 – 0.2 depending on the Higgs mass/final state After all Cuts

  38. Top Quark Precision Measurement in Run 2 Cross Section Cross Check SM with MTop “Rare” Decays Mass Constrain MHiggs Run 1 World Average Top Mass Stay tuned for t’s Run 2 Cross Sections All jets, dilepton, l+jets

  39. Di-Lepton Top Cross Section Small cross section Relatively free of SM backgrounds Instrumental Fakes SM Backgrounds Fakes Estimated on data ALPGEN+Pythia Isolated Lepton Fakes

  40. Dilepton Cross Section Cross section shows some excess which is still consistent with the standard model expectation. We are looking forward to collecting more data!!

  41. Lepton + Jets Systematics Driven Method LP’03 results were close to being systematics driven Fit shapes from likelihood discriminate of signal and background Preselection cuts removes all but W+Jets 1 No B-tagging Determine Topological Variables 2 Create Likelihood Discriminent 3 Fit data to combinations of backgrounds and signal 4 Preselection Cuts include NJets>=4, etc.

  42. Lepton + Jets Topological Variables • Good S:B • Minimize JES • Small Correlations HT2/HZ Sphericity Aplanarity Centrality HT of all but leading jet KTmin KT of #4 jet relative to #3 jet. HT2/HZ KTmin

  43. Lepton + Jets

  44. Lepton + Jets e+Jets m+Jets Total

  45. All Jets Cross Section 46% of ttbar production NN are trained on data for background, and ttbar MC for signal QCD is many orders mag greater Simple Cuts aren’t enough! 6 Jets, exactly one btag HT,H3jT,<Nj>, sphericity, aplanarity, centrality Background Rejecting NN Cut ET4,5, average eta Top Quantity NN Top Hypothesis NN cww, ctt, MWW, Mtt, Mmin1,2, Mmin3,4 Cut

  46. Discriminating Variables Background model is data-derived Variables are designed to address different aspects of the background Energy Scale – HT, sqrt(s) Soft non-leading Jets – H3jT, ET5,6,<Nj> Event Shape – Sphericity, aplanarity Rapidity – Centrality, <h2> Top Properties – Top and W Mass Likelihood, MWW, Mtt, min dijet masses JES Systematics

  47. All Jets Cross Section 0.75 220 events pass all cuts Expect 186 ± 5(stat) ± 7.5(sys)

  48. Top Mass Combination (see Juan’s April 25 2003 W&C) DØ New Run I Top Mass Result is now part of the TeV MTop combination LEP EWWG Old Combination Mt = 174.333 ± 5.141

  49. Really want to talk about… Squeezing Run 2 Top and W Mass Errors Extensive program in place Coming to a Wine And Cheese near you soon… (Old TeV Top Mass)

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