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Measurement of the Forward-Backward Charge Asymmetry( A FB ) in pp→Z/ ɣ * → e + e - at D 

_. Measurement of the Forward-Backward Charge Asymmetry( A FB ) in pp→Z/ ɣ * → e + e - at D . 尹 航. 尹 Center of Particle Physics and Technology University of Science and Technology of China 2010 高能物理学会 第八届全国会员代表大会暨学术年会. Center of Particle Physics and Technology

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Measurement of the Forward-Backward Charge Asymmetry( A FB ) in pp→Z/ ɣ * → e + e - at D 

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  1. _ Measurement of the Forward-Backward Charge Asymmetry(AFB) in pp→Z/ɣ* → e+e- at D 尹 航 尹 Center of Particle Physics and Technology University of Science and Technology of China 2010 高能物理学会 第八届全国会员代表大会暨学术年会 Center of Particle Physics and Technology University of Science and Technology of China

  2. Introduction • Vector and axial-vector couplings of Z boson to fermion: and The presence of both vector and axial vector couplings gives rise to non-zero AFB. Forward Backward • The differential cross section: • Forward-backward asymmetry : 2010高能物理学会, 尹航

  3. Predicted AFB _ uu  e+e- Z/* interference Pure Z exchange Primarily pure * exchange 2010高能物理学会, 尹航

  4. Weak mixing angle sin2W • AFB is sensitive to sin2ϴW • Given α, Gf, and MZ, we can use sin2ϴW to constraint higgs mass Also depends on quark couplings Only depends on lepton couplings 2010高能物理学会, 尹航

  5. Motivation • Test of Standard Model • Forward-backward asymmetry(AFB) • Weak mixing angle • Z to light quark couplings • Sensitive to beyond SM physics 2010高能物理学会, 尹航

  6. Tevatron Collider Chicago - Booster CDF DØ p source Tevatron Main injector & Recycler 2010高能物理学会, 尹航

  7. D detector Uranium Liquid Argon calorimeters Central (CC) and Endcap (EC)‏ Coverage: || < 4.2 Silicon Microstrip Tracker (SMT) Central Fiber Tracker (CFT) 2 T magnetic field Coverage: || < 3.0 • Service work: • Calorimeter calibration • Electron identification Drift chambers and scintillator counters 1.8 T toroids Coverage: || < 2.0 2010高能物理学会, 尹航

  8. Event selections • D data: L = 5.0 fb-1 • Two isolated electrons requirements: • pT > 25 GeV • Shower shape consistent with that of a electron • At least one electron in central calorimeter • Two electrons in central calorimeter(CC), require two opposite charge • Only one electron in CC, require CC electron must have a track match(use the charge of CC electron to determine forward/backward event) 2010高能物理学会, 尹航

  9. MC signals and backgrounds • Signal: Pythia samples: • Z/γ*->ee samples: Mass region(40-1000GeV) passed through Geant simulation of D detector • Generator level: Z-pT rapidity and Z Mass reweighting • Reconstructed level: Tuned to data by applying EM smearing, efficiencies scaling • SM backgrounds: Z->ττ, W+X, WW, WZ, ɣɣ, ttbar • QCD background: measured from real data 2010高能物理学会, 尹航

  10. Data and MC comparison Invariant Mass distribution cosϴ* distribution 2010高能物理学会, 尹航

  11. Unfolding procedure • Unfolding: from reconstruction level to particle level • Detector resolution corrections • Acceptance * efficiency corrections • Charge Mis-identification corrections 2010高能物理学会, 尹航

  12. Unfolded AFB measurement • Source of systematic uncertainties: • Theoretical: PDF, QCD and EW corrections • Electrons: energy scale, energy smear, difference between forward and backward efficiencies, charge mis-identification • Other: background, Acc*eff, the input of sin2ϴW, the unfolding method Work on progress, 5.0 fb-1 2010高能物理学会, 尹航

  13. sin2ϴWeffresults D 1.1 fb-1, Phys. Rev. Lett. 101, 191801 (2008) Work on progress, 5.0 fb-1 • Measured value • Using minimum χ2 fitting method • Main systematic uncertainty comes from PDFs • With more data, combined with muon channel , Tevatron precision will be comparable with the world-average. 2010高能物理学会, 尹航

  14. Z to light quark couplings Work in Progress, 5.0 fb-1 Z-u quark couplings Z-d quark couplings Vector Vector D0 5 fb-1 Syst. D0 5 fb-1 Syst. D0 5 fb-1 Syst. D0 5 fb-1 Syst. Axial-vector coupling Axial-vector coupling 2010高能物理学会, 尹航

  15. Conclusion • Measured AFBwith 5.0 fb-1data • Agrees with PYTHIA prediction • 5 times more data than the previous result (D, Phys. Rev. Lett. 101, 191801 (2008)), will be the most precise measurement at the Tevatron. • Measured • Precision is better than the uncertainty of LEP(HAD combination) , still dominated by statistical uncertainty • With 8-10 fb-1 combine both electron and muon channel with CDF, the expected precision will be comparable with WA • Measured Z to light quark couplings • Will be world’s most precise directly measurement of those couplings • D RunII 1.1 fb-1 has been published in Phys. Rev. Lett. 101, 191801 (2008) • DRunII 5.0 fb-1 paper is under review for publication(PRD). 2010高能物理学会, 尹航

  16. Thank you! 2010高能物理学会, 尹航

  17. BACKUP 2010高能物理学会, 尹航

  18. The DØ Collaboration The sun never sets on the D0 empire! Institutions: 82 total, 38 US, 44 non-US Collaborators: 554 physicists from 18 countries Physics: B, EW, QCD, Top, Higgs, New Phenomena September 2007 2010高能物理学会, 尹航

  19. u/d AFB 2010高能物理学会, 尹航

  20. Weak mixing angle sin2W(cont.) (sin2Weff includes higher order corrections) LEP and SLD most precise results are off by 3 in opposite direction NuTeV result is 3 away from the global EW fit 2010高能物理学会, 尹航 sin2W(N)‏ 0.2277  0.0016

  21. Acceptance*efficiency unfolding • Acc*eff for CCCC and CCEC events • To remove geometric and kinematic cuts effects 2010高能物理学会, 尹航

  22. Charge mis-ID correction • fQ: Charge mis-identification rate • For CCCC events, we have If fQ = 50%, cannot measure charge asymmetry • For CCEC events, we have • Measured fQ vs. Mee in analysis 2010高能物理学会, 尹航

  23. Charge mis-ID rate • The rate of same-sign events as a function of di-electron invariant mass data MC Very few events for Mee > 200 GeV • Data • MC Mis-ID rate shape determined from MC • MC cannot describe the data for charge mis-ID rate: • normalized MC distribution to data in the Z peak region • Use data statistical uncertainty 2010高能物理学会, 尹航

  24. Source of systematic uncertainties • Theoretical: PDF, QCD and EW corrections • Electrons: energy scale, energy smear, difference between forward and backward efficiencies, charge mis-identification • Other: background, Acc*eff, the input of , the unfolding method  AFB  AFB 2010高能物理学会, 尹航

  25. Z to light quark couplings • Use raw AFB and reweight PYTHIA into ZGRAD2(higher order corrections) to do this measurement • Also tried other methods • Use raw AFB and reweight PYTHIA to Resbos • Use unfolded AFB and Zgrad2 Three different methods are very consistent with each other 2010高能物理学会, 尹航

  26. Unfolding: Response Matrices • Due to the finite detector resolution, events migrate into other mass bins • At generate level: and • At selected level: and 2010高能物理学会, 尹航

  27. AFB measurement at LEP and SLD • Left- and right-handed couplings: gV = gL+gR, gA = gL-gR • Fermion asymmetry parameter: Af = 2gVgA/(g2V+g2A)‏ • At e+e- collider: • Forward-backward asymmetry: • AfFB = (fF-fB)/(fF+fB) = 0.75AeAf • Left-right asymmetry: • ALR = (L-R)/(L+R) = PeAe • Left-right F/B asymmetry (direct measurement of final-state coupling)‏ • ALRFB = [(LF-RF)-(LB-RB))]/[(LF+RF)+(LF+RF)] = 0.75PeAf 2010高能物理学会, 尹航

  28. Measurement Techniques used at SLD and LEP • Measurement of ALR, AFBLR, AlFB at SLD: • Excludes electron mode to avoid the added complexity of correcting for t-channel interference • Determination of the beam polarization • Measurement of AlFB at LEP • Measurement of P( polarization)‏ • Measurement of AbFB, AcFB • Use lepton tag: P and PT of leptons can be used to assign a probability that the lepton is a b or a c quark • Sign of the lepton tags the quark charge • Measurement of QhadFB: • Use momentum-weighted jet charge to tag the quark charge • Relies on MC to determine the relative abundance of the different quark species 2010高能物理学会, 尹航

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  33. Normalized differential cross section • Normalized differential cross section: Number of selected events Number of background events Bin width Integrated luminosity Acceptance * efficiency effects 2010高能物理学会, 尹航

  34. sin2Weff depends on scale • Moller scattering • -nucleon scattering • Atomic parity violation in Cesium 2010高能物理学会, 尹航

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