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Tests of the Standard Model at the Tevatron

Tests of the Standard Model at the Tevatron. Trends in HEP Yalta Crimea Conference. Mark Adams University of Illinois at Chicago Representing the D0 and CDF Collaborations. Tevatron Tests of the Standard Model. Standard Model Electroweak Measurements W, Z Diboson Top

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Tests of the Standard Model at the Tevatron

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  1. Tests of the Standard Model at the Tevatron Trends in HEP Yalta Crimea Conference Mark Adams University of Illinois at Chicago Representing the D0 and CDF Collaborations Trends in HEP Yalta Crimea Conference Sept. 2006

  2. Tevatron Tests of the Standard Model Standard Model Electroweak Measurements W, Z Diboson Top selection, methods Properties cross section single top Higgs search Focus on top,W,Z and the missing Properties depend on each other through higher order corrections Higgs Trends in HEP Yalta Crimea Conference Sept. 2006

  3. Tevatron Luminosity Typical data samples in this talk ~350, ~950 pb-1 2 fb-1 soon 4-8 fb-1 by 2009 Important analysis tools Lepton triggering and ID b-tagging jet resolution MET (e.g. calibrated with dijet data) 4-8 fb-1 expected by end of 2009 Mar. 2001 – July 2006 1 fb-1 Run I Lumi 1000 pb-1period Trends in HEP Yalta Crimea Conference Sept. 2006

  4. n e+,m+ Bosons and Dibosons Efficient lepton triggers and selection Electron, muon, MET calibrations key Z peak from LEP Backgrounds QCD and DY very small Must model data & calibrate energy scale to obtain widths Extract W mass from edge of distribution Z(ee) W(en) Trends in HEP Yalta Crimea Conference Sept. 2006

  5. H X b W W W W W W t X W DmW ~ mt2 New Physics DmW ~ ln(mH) W mass Extract W mass from fit of Jacobian edge mT2 = 2pTlpTn(1-cosdf) Radiative Corrections – introduce weak dependence on mt, MH, mX Systematic errors is the whole game RII will eventually improve results LEP 80.392+-0.039 GeV Tev R1 80.452+-0.059 GeV edge Trends in HEP Yalta Crimea Conference Sept. 2006

  6. W Width sW*BR(W-ln) R= Extract GW assuming SM (s and GW-ln),LEP for Z BR R=10.84+-0.15 +-0.14 GW=2.092+-0.042 CDF D0 R=10.82+-0.16 +-0.25+0.13(pdf) sZ*BR(Z-ll) Trends in HEP Yalta Crimea Conference Sept. 2006

  7. Inclusive W, Z Cross Sections Central lepton triggers Lepton ID and trigger efficiency critical Small backgrounds (QCD, DY) subtracted Systematic errors 2% Luminosity 6% NNLO theory 2-3% 70-350 pb-1 samples NNLO Hamberg, van Neervan, Matsura 191; Anastasiou, 2004 W Z Trends in HEP Yalta Crimea Conference Sept. 2006

  8. trilinear boson vertex Diboson Production Sensitive to SM trilinear vector boson coupling – depends on q2 Cross section and kinematics also sensitive to anomalous couplings ZZ not ready yet Trends in HEP Yalta Crimea Conference Sept. 2006

  9. Inclusive WZ SM Production D0 WZ Candidate Mass versus Missing ET three leptons plus MET Trends in HEP Yalta Crimea Conference Sept. 2006

  10. WZ to lnll Evidence from D0 12 trilepton events observed in 760-860 pb-1 Expect 7.5 1.2 signal and 3.6 0.2 background 3.3seffect s(WZ) = 3.98 pb NLO prediction is 3.7 pb +1.91 -1.53 Trends in HEP Yalta Crimea Conference Sept. 2006

  11. W, Z and Diboson cross sections Triple Vertex Coupling has been measured Cross sections for W,Z, Wg, Zg and WW(ll) and WZ(lll) are found to agree with SM ZZ is next challenge Trends in HEP Yalta Crimea Conference Sept. 2006

  12. Top – what do we know? dm/m <2% (combined) Last of particle of 3 families structure Massive Charge +2/3 t -> Wb Spin Short lifetime -4/3 excluded at 95%C.L.(D0) ~100% Not directly ct<52.5mm at 95%C.L.(CDF) Trends in HEP Yalta Crimea Conference Sept. 2006

  13. Top event selection Decay modes define topologies: dilepton lepton+jet all hadronic Trends in HEP Yalta Crimea Conference Sept. 2006

  14. Top Mass – Combined Tevatron Mass lower than previous years (shift from 175) Dominated by l+j weights CDF 62% and D0 19% (different lumi) RunII in-situ JES from W-qq’ in l+j Trends in HEP Yalta Crimea Conference Sept. 2006

  15. Top Mass CDF and D0 All channels shown New promise - CDF average b decay length independent of JES Some possible channel dependence –watch in future Trends in HEP Yalta Crimea Conference Sept. 2006

  16. Top Lifetime Measurement Top quark decays before hadronizing CDF measures lifetime upper limit in e and m channels. Compare track impact param from Z decays to top events to extract ct ct<52.5mm at 95%C.L. Modeled Observed in Z Observed in top Trends in HEP Yalta Crimea Conference Sept. 2006

  17. Top quark lifetime limit ttbar events selection: electron/muon, >= 3 jets containing a secondary vertex tagged jet; large missing energy. Search for long-lived top Electron/muon tracks from Z determine the detector resolution, : cτ < 52.5 μm @ 95% CL Trends in HEP Yalta Crimea Conference Sept. 2006

  18. Top Quark Charge Pt-weighted charge of lepton and b-jet Can’t measure charge directly but can rule out exotic. Selection: 2 isolated leptons, large MET, >3 jets, 2 b-tagged jets Measure charge of top under two charge assumptions: +2e/3 and -4e/3 4e/3 charge excluded to 94% C.L. Trends in HEP Yalta Crimea Conference Sept. 2006

  19. tt Resonances CDF Can ttbar come from a resonance? Stringent limits. Trends in HEP Yalta Crimea Conference Sept. 2006

  20. CDF 955pb-1 W-Boson Helicity Fractions in Top-Quark Decays Use fully reconstructed top events. Top decays before hadronizing – decays keep helicity info cosq* uses angle between top and lepton in the W rest frame fraction of longitudinally (f0) and right-handed (f+) polarized W bosons f0= 0.61 ± 0.12 ± 0.06 with f+ fixed to zero, f+= -0.06 ± 0.06 ± 0.03 with f0 fixed to the SM expectation of 0.70. f+ < 0.11 at 95% CL D0 f+= 0.00 ± 0.13 ± 0.07 D0 determines f+ < 0.25 at 95% CL Right Handed W excluded at 10% level Trends in HEP Yalta Crimea Conference Sept. 2006

  21. Single Top Production via Weak Interaction Test of SM – does single top production exist? • Cross Section proportional to |Vtb|2 • Test of CKM matrix unitarity: Vut2+Vct2+Vbt2 =1 Sensitive to 4th generation Same channel as WH - Wbb t-channel 1.98 pb s-channel 0.88 pb Trends in HEP Yalta Crimea Conference Sept. 2006

  22. Single Top selection - D0 Isolated lepton (e or m) pT> 15 GeV; |h e|<1.1 or |hm|<2.0 Missing ET> 15 GeV Between 2-4 jets ET>15GeV; |h|<3.4 1 jet ET> 25 GeV 1 or more b-tags D0 analysis (370pb-1) CDF analysis (695pb-1) described by N. Giokaris Trends in HEP Yalta Crimea Conference Sept. 2006

  23. Sample of discriminant inputs Discriminants built to distinguish s or t channel from backgrounds tt and W+j Ql*hleading-jet Trends in HEP Yalta Crimea Conference Sept. 2006

  24. Likelihood Discriminant Results s(t) < 4.4pb s(s) < 5.0pb Approaching SM predictions Updated results expected soon from both experiments Data sets – separate electron/muon and 1 b-tag/ >1 b-tag (4 sets) With 4 signal-background pairs:,s-channel/W+jets, s-channel/ttbar, t-channel/W+jets and t-channel/ttbar) 16 LD – combined fit to 4 2D distributions e.g. Likelihood Discriminants for s-channel/t-channel vs ttb/ W+jets Trends in HEP Yalta Crimea Conference Sept. 2006

  25. Decays Production mH (GeV/c2) SM Higgs Production and Decays pb Dominant Decays bb for MH < 135 GeV WW* for MH > 135 GeV Search strategy: MH <135 GeV:associated production WH and ZH with Hbb decay Backgrounds: Wbb, Zbb, top, WZ,QCD+ leptonic WWW* & WW* MH >135 GeV:gg H production with decay to WW* Backgrounds: WW, DY, W/ZZ, tt, tW, + leptonic with WWW* Trends in HEP Yalta Crimea Conference Sept. 2006

  26. LEP EWWG fit Constraints on the Higgs mass LEP1 and SLD indirect measurements LEP2 and Tevatron 114 GeV limit; mW; mtop Light Higgs Preferred 85 GeV upper limit of 166 GeV +39 -28 Trends in HEP Yalta Crimea Conference Sept. 2006

  27. SM Higgs SM tested precisely but mass of Higgs unknown. Mass is related to other measureables via loops Low mass Higgs is preferred Standard Model Simplest Higgs mechanism possible (doublet field -> 1 physical Higgs particle) Higgs is a singleneutral scalar particle Interacts with all SM particles but couples more strongly with more massive particles LEP EWWG • LEP Direct limit: MH > 114 GeV at 95% • New CDF/D0 top mass (171.4  2.1 GeV) New LEP W mass (80.392  0.029 GeV) • MH = 85 +39-28 GeV • MH < 166 GeV at 95 % CL Trends in HEP Yalta Crimea Conference Sept. 2006

  28. SM Heavy Higgs: H  WW*  lnln 2 high Pt leptons and missing Et spin 0 Higgs – WW - leptons prefers same direction No Higgs mass peak! CDF and DØ published on 0.3-0.4 fb-1 H 4th generation? CDF Trends in HEP Yalta Crimea Conference Sept. 2006

  29. H  WW*  lnln D0 Update W + jet/g production: Updated DØ analysis: L ~ 950 pb-1 in H  WW*  ee and em L ~ 930 pb-1 in H  WW*  mm • Selection Strategy: • Presection:lepton ID, trigger, opposite charge leptons • Remove QCD and Zl+l-:ET > 20 GeV • Higgs Mass Dependent Cuts:Invariant Mass (Ml+l-); Min. Transverse Mass Sum of lepton pTl and ET (S pTl + ET) • Anti tt(bar) cut: HT = S PTjet < 100 GeV • Spin correlation in WW pair:Df(l,l) < 2.0 Major backgrounds WW production Trends in HEP Yalta Crimea Conference Sept. 2006

  30. Results for HWW* Expected/Observed # of events for mH = 160 GeV (L ~ 950 pb-1): mm 9 9.8±0.8 6.6±0.1 1.0±0.4 0.6±0.4 0.5±0.1 0.5±0.10.6±0.60.35 mm If mH= 160 GeV,  ~ 2 higgs in our sample! SM only a factor 4 away We exclude 4th generation models, for which mH=150-185 GeV WW slides G. Benardi Trends in HEP Yalta Crimea Conference Sept. 2006

  31. WHWWW* (360-380 pb-1) 2 like-sign leptons (one from H and one from W) Important in intermediate mass region 125-145 GeV Backgrounds: WW, WZ, sign flips and QCD fake leptons Events after preselection Trends in HEP Yalta Crimea Conference Sept. 2006

  32. Final Selection for WWW* Topological Likelihood discriminant, built on 3 variables per channel Trends in HEP Yalta Crimea Conference Sept. 2006

  33. Exclusion limit for WWW* Events after Topological Likelihood discriminant Effect on global combination significant in the intermediate region (125-145 GeV) Trends in HEP Yalta Crimea Conference Sept. 2006

  34. Combined Higgs boson Search at DØ ZH -llbb ZH -nnbb WH -WWW Low statistics (0.3 fb-1) cross-section factors Data/SM: ~ 15 at 115 GeV ~ 9 at 160 GeV CDF and D0 may reach exclusion for a 115 GeV Higgs with 3 fb-1 of data! With high statistics (1 fb-1) Data/SM = ~ 5 at 160 GeV Trends in HEP Yalta Crimea Conference Sept. 2006

  35. Combined Tevatron SM Higgs mH Limit/SM (GeV)Observed 115 10.4 130 10.6 160 3.9 180 5.8 Quickly approaching sensitivity required to exclude the Higgs at the Tevatron Trends in HEP Yalta Crimea Conference Sept. 2006

  36. Expected Improvements at DØ and CDF • D0 • New b-tagging tool based on Neural Net - improves efficiency 33% at 0.5% fake rate • Jet Energy Resolution (recalibration+track jet algorithm: add momentum from out of cone trks) 20% improvement • Calibrate b jet with Zbb • DØ Upgrade • L1Cal Trigger - Efficiency improvement for (ZHnnbb, hbb) • L0 silicon tracking improves b-tag • CDF • Increase acceptance forward: muons and improved tracking and b-tagging Add additional channels: • in the WH and WW analyses tau-leptons have not been used. • Improve jet resolution • Neural Networks, better optimization Trends in HEP Yalta Crimea Conference Sept. 2006

  37. Tevatron SM Higgs Search Prospects updated in 2003 in the low Higgs mass region W(Z) H ln(nn,ll) bb optimization of analysis Ldt (fb-1) Sensitivity in the mass region above LEP limit (114 GeV ) begins at ~2 fb-1 With 8 fb-1 exclusion 115-135 GeV & 145-180 GeV, 3-sigma discovery/evidence at 115 – 130 GeV Tevatron8 fb-1 LEP Excluded Using knowledge from recent data (use D0 300 pb-1; add improvements at both experiments) extrapolate exclusion limit: • At 115 GeV need ~3 fb-1 • At 160 GeV need ~5 fb-1 • 95% CL exclusion for mH= 115-185 GeV with 8 fb-1 Trends in HEP Yalta Crimea Conference Sept. 2006

  38. Conclusions Standard Model is being tests at the percent level W, Z and diboson cross sections match SM Top quark Properties, mass, cross sections as expected Single Top sensitivity reaching observational level Bs oscillations observed SM Higgs – Combining channels and experiments demonstrates exclusion possible up to 185 GeV mass by 2009. Trends in HEP Yalta Crimea Conference Sept. 2006

  39. Backup Slides Trends in HEP Yalta Crimea Conference Sept. 2006

  40. H  WW*  ee / em / mm (950-930 pb-1) Preselection: Trigger, ID, leptons of opposite charge: pTl1 = 15 GeV; pTl2 = 10 GeV m m e e e m Missing Transverse Energy > 20 GeV Cut (to suppress Z/g*  l+l- background) e e e m m m Trends in HEP Yalta Crimea Conference Sept. 2006

  41. HWW* : final selection mm ee em lepton-lepton Df Final selections MH=160GeV (x10) Trends in HEP Yalta Crimea Conference Sept. 2006

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