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W and Z physics at CMS

W and Z physics at CMS. G. Franzoni University of Minnesota On behalf of the CMS collaboration LHC Days - Split Oct 5th, 2010. outline. Physics motivation Leptons and mE T at CMS W and Z signal extraction Inclusive W and Z cross sections with 0.198 pb -1 Differential measurements:

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W and Z physics at CMS

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  1. W and Z physics at CMS G. Franzoni University of Minnesota On behalf of the CMS collaboration LHC Days - Split Oct 5th, 2010

  2. outline • Physics motivation • Leptons and mET at CMS • W and Z signal extraction • Inclusive W and Z cross sections with 0.198 pb-1 • Differential measurements: • Lepton charge asymmetry • W + jets G. Franzoni UMN - CMS

  3. Why are W and Z interesting • Discovered nearly three decades ago… • Tools for commissioning: • Calibration and alignment • Source of isolated high PT leptons • Production theoretically well understood • Early physics probes: • Cross sections at 7 TeV • Constrain PDF at LHC • Understand background for many physics searches G. Franzoni UMN - CMS

  4. CMS Electromagnetic calorimeter in CMS CMSWeight 14000t Diameter 15m Length 21.6m Magnetic field 3.8T HCAL Muon chamber: Drift Tubes, CSC and RPC’s Tracker: Si strips and pixels Beam pipe ECAL+ PbWO4 Crystals+Si/Pb Preshower 3.8T solenoid Trigger - L1: hardware w/ output 100 kHz - HLT: farm of pc’s w/ same framework offline, O(102) Hz Iron yoke

  5. Datasets • CMS recorded now 10 pb-1, with efficiency in excess of 90% (and growing) • Data : • Analysis presented here: 198 nb-1 • Ever growing dataset included in this analysis. Update with 2.9pb-1 • MC: • NLO Monte Carlo (POWHEG) for EWK processes • PYTHIA for QCD and t tbar • PYTHIA for hadronization • Detector simulation with GEANT4 G. Franzoni UMN - CMS

  6. Muon reconstructions and selection • HLT trigger: pT > 9 GeV/c • Kinematics: • pT > 20 GeV/c • μ1 :|η|<2.1 μ2 for Z:|η|<2.4 • Track quality: • Matching hits in tracker (10) pixel (1) and at least 2 muon stations • χ2/ndf<10; d0 cut reject cosmics • Isolation: in cone of ΔR<0.3 • W: relative isolation from tracker and calorimeters • a < 0.15 • Z: absolute tracker isolation • < 3 GeV/c G. Franzoni UMN - CMS

  7. Electron selection • HLT trigger: cluster ET>15 GeV • Kinematics: • ET > 20 GeV • 0.<||<1.442 or 1.566<||<2.5 • Clustering and tracking customized to recover bremsstrahlung losses • Identification: cluster-track matching, e.m. shower shape and hadron leakage H/E • Isolation: • Isolation from tracker, ECAL and HCAL relative to electron PT • Sum PT within cone of ΔR<0.3, removing electron ‘footprint’ Background enriched Signal enriched G. Franzoni UMN - CMS

  8. Missing ET • Cleaning of instrumental and beam-induced background. Remove hits: • with unphysical pulse shapes or energy sharing across cells in calorimeters • matching parallel-to- beam trajectories • Two ways of exploiting excellent CMS tracking to reconstruct mET: • Track-corrected mET • sum calorimeter towers and replace towers ET with pT of matched charged tracks • Particle Flow mET • vector sum of of all particles identified in the event • PF mET used in this analysis, track-corrected for cross-check min bias di-jets G. Franzoni UMN - CMS

  9. W cross section W eν candidate Wμν candidate G. Franzoni UMN - CMS

  10. Yield Wμν • Veto presence of second μ with pT>10 GeV/c to remove Z and DY • Wμν yield determined from simultaneous MT(W) fit to signal and background contributions with fixed shape • QCD background shape from data, by inversion of isolation cut > 0.2 • Fair agreement of data-driven shape with MC inverted and non-inverted. • Difference treated as systematic • Signal Wμνand EWB background (DY, τ, ttbar) shapes from MonteCarlo NW=818±27 G. Franzoni UMN - CMS

  11. W μν cross section NW=818±27 NW+=529±24 NW-=289±13 • Total Wμνcross section: • Separate positively and negatively charged W: G. Franzoni UMN - CMS

  12. Yield W eν • Veto presence of second electron with ET>20 GeV • Weν yields determined from simultaneous mET(W) fits to signal and background contributions with fixed shape: • QCD background shape: • modelled with Rayleigh distribution • Constrained to background-enriched sample obtained by tack-cluster matching cut inversion • Shapes of signal Weνand EWB background obtained from MonteCarlo (POWHEG) G. Franzoni UMN - CMS

  13. W eν cross section • Total Weνcross section: • Separate positively and negatively charged W: G. Franzoni UMN - CMS

  14. systematic uncertainties on W lν • Main uncertainty from luminosity • Other uncertainties of statistical origin, will decrease in the 2.9pb-1: • efficiencies: measured from MC and corrected with data-drive scale factors (Z events). Uncertainties on factors enter systematics • momentum scale (<1%) and cluster energy scale (<3%) • Scale of mET: estimate <10% from data-MC comparison of W recoil • Impact of PDF on acceptance (CTEQ66, MSTW08NLO, NNPDF2.0) G. Franzoni UMN - CMS

  15. Z cross section Z ee candidate Z μμ candidate G. Franzoni UMN - CMS

  16. Zμμ cross section • Selection: • Opposite-charge μ’s; relaxed selection for μ2 (10 TK matching hits) • 60< mμμ <120 GeV • Predicted background QCD+EWK negligible (≈0.3%) • Cross section: NZ=77 G. Franzoni UMN - CMS

  17. Zee cross section • Selection: • Opposite-charge e’s; same cuts as W, but at looser working point (ε: 80->95%) • 60< mee <120 GeV • Predicted background from di-jets less than one event • Systematic assigned to the impact of energy scale • Update with 2.9pb-1: scale recalibrated (consistent with π0 and η in ECAL barrel) • Cross section: NZ=61 G. Franzoni UMN - CMS

  18. systematic uncertainties on Z ll • Main uncertainty from luminosity • Other uncertainties of statistical origin, will decrease in the 2.9pb-1: • efficiencies: measured from MC and corrected with data-drive scale factors (Z events). Uncertainties on factors enter systematics • momentum scale (<1%) and cluster energy scale (<3%) • Impact of PDF on acceptance (CTEQ66, MSTW08NLO, NNPDF2.0) G. Franzoni UMN - CMS

  19. W and Z cross sections • Lepton channels combined w/ likelihood accounting errors and their correlations • Cross sections compatible with Standard Model G. Franzoni UMN - CMS

  20. Differential results with 198 nb-1 G. Franzoni UMN - CMS

  21. W+ and W- separately • The prevalence of u quarks in protons yields larger rate of W+ than W- • R(W+/W-) relevant to constrain PDF at low-x W+lν W-lν R(W+/W-) G. Franzoni UMN - CMS

  22. W charge asymmetry • Slicing the asymmetry in bins of lepton pseudo-rapidity: • With 198nb-1 dominated by statistical uncertainties • 0.05-0.08 • Systematic of 0.03 estimated for both leptons (~10pb-1): • Efficiencies and background subtraction • Different kinematics results in small acceptance differences for W+ and W- G. Franzoni UMN - CMS

  23. W+Jets associated production • Important background to many analyzes and searches • Powerful tool to test perturbative QCD C. Lazaridis – Poster: “W/Z + Jets production measurements with 7 TeV pp collisions data at CMS experiment” • Reconstruction of jets: • Particle flow objects • Anti-Kt algorithm (ΔR<0.5) G. Franzoni UMN - CMS 23

  24. 2.9pb-1 W and Z cross section update G. Franzoni UMN - CMS

  25. 2.9pb-1 update for W μν G. Franzoni UMN - CMS

  26. 2.9pb-1 update for Z ll • Update to electromagnetic energy scale in ECAL G. Franzoni UMN - CMS

  27. Conclusions and outlook • Electroweak physics program in full swing at CMS! • Reported: • W and Z cross section at 7 TeV • First differential measurements • LHC delivering ever growing luminosities: we’ve entered the phase of precision measurements. • Soon an update on the Z/W inclusive cross section measurement • 2010 full dataset for differential measurements G. Franzoni UMN - CMS

  28. References • “Measurement of the W and Z inclusive production cross sections at sqrts=7 TeV with the CMS experiment at the LHC”, CMS-PAS-EWK-10-002 • “Missing Transverse Energy Performance in Minimum-Bias and Jet Events from Proton-Proton Collisions at √s = 7 TeV”, CMS-PAS-JME-10-004 • “Electron Reconstruction and Identification at √s = 7 TeV”, CMS DP-2010/032 G. Franzoni UMN - CMS

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