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The W and Z Cross Sections at D Ø in Run 2

The W and Z Cross Sections at D Ø in Run 2. Georg Steinbr ü ck Columbia University, New York On behalf of the D Ø collaboration DPF 2003, Philadelphia, PA. Introduction + Motivation W/Zmuons W/Z electrons. Why do we care about W/Z Production?. New CM energy: 1.8TeV  1.96 TeV

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The W and Z Cross Sections at D Ø in Run 2

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  1. The W and Z Cross Sections at DØin Run 2 Georg Steinbrück Columbia University, New York On behalf of the DØ collaboration DPF 2003, Philadelphia, PA • Introduction + Motivation • W/Zmuons • W/Z electrons DPF 8-April-2003

  2. Why do we care about W/Z Production? New CM energy: 1.8TeV 1.96 TeV CS increase by ~9% • Test of SM couplings • Test of higher order QCD corrections • constrain proton PDFs • Gain understanding for Precision EW measurements: • W mass and width • W can be used to determine luminosity • Tuning of algorithms and Triggers • W+jets Background to top and Higgs signals DØ Run 2a Prediction DPF 8-April-2003

  3. p l q q W(Z) p n (l) W and Z Production Mechanics - • Production dominated by qqannihilation • Due to very large pp jj production, need to use leptonic decays • W  ln (BR ~ 11% per mode) • Z ll (BR ~ 3% per mode) • Distinctive event signatures • High pT isolated leptons (e or m) • One high pT lepton + Missing ET (W) • Two high pT leptons (Z) • Low backgrounds • Large samples • Well understood EW vertex • Test QCD - O(as0) W’s are produced at ~1 Hz @Run 2 Millions of W’s 100k Z’s DPF 8-April-2003

  4. W and Z Cross Sections A counting experiment… Backgrounds These measurements use data taken Sept ’02Jan ‘03 Integrated Luminosity Acceptance from Monte Carlo Efficiencies from data where possible DPF 8-April-2003

  5. The DØ Run 2 Detector All parts of the detector used in EW analyses: Calorimeter/ Muon System and the Tracker SMT DPF 8-April-2003

  6. The Muon Detector • Two regions: Central and Forward • Coverage up to=±2. • Three layers: one inside (A), two outside (B, C) the toroid magnet • Consists of scintillators and drift tubes Drift Tubes Shielding scintillators DPF 8-April-2003

  7. # events Dt(ns) Z Production (Muon Channel) sqrt(s) = 1.96 TeV 32 pb-1 • Z selection • 2 tracked, oppositely-charged m’s with pT>15 GeV& |h|<1.8 • Di-muon trigger • At least one muon is isolated • (DR)2=(Dfmm)2+(Dhmm)2 >4.0 • |Dt| < 9 ns in scintillator • NO explicit mass requirement • Background is small • b-bbar is 1+-1% • Z to tt is 0.5+-0.1% DPF 8-April-2003

  8. eL1 = 87+/-2% etrk= 82+/-1% tag m PT Zmm: Efficiencies • Acceptance from MC (40+/-1%) • Efficiencies from data mtag L1+L2, central track Z L1 OR no L1 mprobe track OR no track m ID eff’y emuID = 91+/-1% DPF 8-April-2003

  9. Z Production (Muon Channel) • Drell-Yan contribution • Correct for 12+-1% DY+interference, determined from Pythia (4%, if restricted to 75<M(mm)<105 GeV) 1585 Candidates in 32 pb-1 D0’s first Zmm cross section in Run 2! DPF 8-April-2003

  10. Wmn: Data Selection • Trigger: • L1: Scintillator based single muon trigger (no pT cut) • L2: At least one muon with pT>5 GeV • L3: At least one track with pT>10 GeV L=17 pb-1 • Offline • One isolated muon matched with central track, pT>20 GeV • In fiducial region of the trigger: |h|<1.6 • Muon corrected Missing transverse energy > 20 GeV • no second muon in event (Zmm veto) DPF 8-April-2003

  11. Wmn: Efficiencies Muon reconstruction efficiency: From calorimeter Muons (Track + Calor deposit) 1m+1 calor only 2m’s Trigger efficiencies (wrt offline) L1 L2 L3 DPF 8-April-2003

  12. Wmn 7352 Candidates in 17 pb-1 QCD background estimated from data. • Backgrounds: • bb, bmn where m passes isolation cut • 5.8%, subtracted from above distributions • Other: • Zmm: ~9% • Wtnmnnn: 3.6% DPF 8-April-2003

  13. Wmn: Result D0’s First Wmn Cross section in Run2! DPF 8-April-2003

  14. W/Z e: The Calorimeter • Using Run 1 calorimeter • Uranium-Liquid Argon • stable, uniform response, rad. hard, fine segmentation • Uniform, hermetic coverage || < 4.2 • Good energy resolution • New readout electronics to operate in Run 2 environment DPF 8-April-2003

  15. W/Ze: Event Selection • Trigger: • L1: 1 calorimeter tower > 10 GeV (or 2 > 5 GeV) • L3: Electron candidate > 20 GeV, shower shape cut L=42 pb-1 • Electrons: • Isolated EM Cluster in the Calorimeter, ET> 25 GeV with large EM fraction, Shower shape consistent with MC expectation • Wen • Missing transverse energy > 25 GeV • Electron candidates matched with central tracks • Zee • 70 GeV < mee < 110 GeV DPF 8-April-2003

  16. Efficiencies • Estimated from Zee events • Require one tight electron. The second electron can be used as an unbiased probe • Efficiencies per electron: • Trigger 98+/- 2% • EMF, isolation ~100% • Shower shape 86+/-1% • Tracking + Matching 73+/-2 % 2nd electron passes/fails Shower shape cut DPF 8-April-2003

  17. Zee QCD background removed by fitting to signal and background 1139 Candidates in 42 pb-1 DY contribution small (1.7%) due to 70 GeV < mee < 110 GeV DPF 8-April-2003

  18. Wen: Backgrounds • Dominant background from QCD multijet events • Estimated from data • Nloose = NW + Nb • Ntight = NWetrk + Nbef loose tight Solve for NW tight = loose +track match From QCD dijet sample • Other backgrounds: • Wtnennn (1.5 %, MC) • Zee (very small) 2.3+/-1% DPF 8-April-2003

  19. Wen: Data versus MC ET ET Agreement between data and MC 27370 Candidates in 42 pb-1 We understand the detector and backgrounds mT DPF 8-April-2003

  20. Putting it all together DPF 8-April-2003

  21. Results W Z C. R. Hamberg, W.L. van Neerven and T. Matsuura, Nucl. Phys. B359 (1991) 343 CTEQ4M PDF DPF 8-April-2003

  22. Conclusions • W and Z cross sections: • Test consistency with SM • QCD corrections • Sensitive to PDFs • W’s can and will be used for luminosity determination • Benchmark measurements for understanding our detector • Four new W and Z cross section measurements • D0’s first Run2 W/Z CS measurement in the Muon channel! DPF 8-April-2003

  23. Spares DPF 8-April-2003

  24. Results DPF 8-April-2003

  25. Wmn Background estimated from data. • Dominant background: • bbar, bmnevents where the muon passes isolation cuts DPF 8-April-2003

  26. Wmn DPF 8-April-2003

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