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W and Z Boson Physics with the CMS Experiment

W and Z Boson Physics with the CMS Experiment. QCD@LHC 2012 Jeffrey Berryhill , Fermilab On behalf of the CMS Collaboration August 20, 2012. Outline. W and Z inclusive cross sections at 8 TeV W lepton charge asymmetry at 7 TeV Drell -Yan differential cross sections at 7 TeV

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W and Z Boson Physics with the CMS Experiment

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  1. W and Z Boson Physics with the CMS Experiment QCD@LHC 2012 Jeffrey Berryhill, Fermilab On behalf of the CMS Collaboration August 20, 2012

  2. Outline • W and Z inclusive cross sections at 8 TeV • W lepton charge asymmetry at 7 TeV • Drell-Yan differential cross sections at 7 TeV • Drell-Yan differential forward-backward asymmetry at 7 TeV Jeffrey Berryhill, Fermilab -- QCD@LHC Workshop August 20 2012

  3. W and Z Cross Sections@8 TeV • pQCD predicts a 15-20% cross section increase as the proton beam energy increases from 7 TeV to 8 TeV • W/Z and W+/W- cross section ratios (and 7/8 double ratios) are (sub-)percent predictions of pQCD • Important initial experimental benchmarks for precision physics with leptons at 8TeV • 1% experimental (non-lumi, non-theory) precision achieved at 7 TeV with just 36 /pb • (J. High Energy Phys. 10 (2011) 132) Jeffrey Berryhill, Fermilab -- QCD@LHC Workshop August 20 2012

  4. W and Z Cross Sections@8 TeV CMS-PAS-SMP-12-011 • To swiftly reproduce the 2010 7 TeV W cross section precision at 8 TeV, 2010-like pileup and triggers were required • During the 2012 intensity ramp-up, while opportunity costs were still low, CMS requested for a couple of fills that the LHC transversely offset the beams from one another in CMS by a few transverse sigma. This reduced mean pileup to ~5 interactions @L=3-6E32 • A special trigger menu with 2010-like, low-threshold, loose single lepton triggers (22 GeV e, 15 GeV mu) was deployed for these runs • 19 /pb were accumulated in this configuration. We do not expect more such runs in 2012. Jeffrey Berryhill, Fermilab -- QCD@LHC Workshop August 20 2012

  5. Z Cross Sections@8 TeV • Z to mumu analysis: • Opp sign mu pairs with PT > 25 GeV and |eta| < 2.1 • Pair mass 60-120 GeV • 6000 candidates, ~0 background, 1.3% stat. • Z reconstruction, ID, trigger efficiency known to 1.1% syst. from tag and probe methods • Excellent lineshape description from POWHEG+PYTHIA Jeffrey Berryhill, Fermilab -- QCD@LHC Workshop August 20 2012

  6. Z Cross Sections@8 TeV • Z to ee analysis: • Opp sign e pairs with PT > 25 GeV and |eta| < 2.5 • Pair mass 60-120 GeV • 5000 candidates, ~0 background, 1.4% stat. • Z reconstruction, ID, trigger efficiency known to 2.8% syst. from tag and probe methods • Excellent lineshape description from POWHEG+PYTHIA Jeffrey Berryhill, Fermilab -- QCD@LHC Workshop August 20 2012

  7. Z Cross Sections@8 TeV • Z cross section dominated by lumi (4.4%) and acceptance theory error (2-3%). • Agreement with FEWZ + MSTW08 total NNLO cross section Jeffrey Berryhill, Fermilab -- QCD@LHC Workshop August 20 2012

  8. W Cross Sections@8 TeV • W muv analysis: =1 muon PT > 25GeV, |eta| < 2.1, 81k W’s • No MET cut, signal extracted via binned MLH simultaneous fit of MET to isolated and non-isolated muons. Signal,QCD yields + 2 QCD shape parameters floating. • W signal MET model corrected with Z recoil data • Lepton efficiency dominant exp. error (1%) Jeffrey Berryhill, Fermilab -- QCD@LHC Workshop August 20 2012

  9. W Cross Sections@8 TeV • W ev analysis: =1 electron PT > 25GeV, |eta| < 2.5, 75k W’s • No MET cut, signal extracted via binned MLH fit of MET. Signal,QCD yields + 2 QCD shape parameters floating. • W signal MET model corrected with Z recoil data (0.9% syst) • Lepton efficiency dominant exp. error (2.5%) Jeffrey Berryhill, Fermilab -- QCD@LHC Workshop August 20 2012

  10. W Cross Sections@8 TeV • W cross section dominated by lumi (4.4%) and acceptance theory error (2-3%). • Agreement with FEWZ + MSTW08 total NNLO cross section Jeffrey Berryhill, Fermilab -- QCD@LHC Workshop August 20 2012

  11. W and Z Cross-Section Ratios@8 TeV • W/Z ratio: • acc. ratio theory error 2% (2.5%) for e (mu) • Exp. error 3.9% (1.7%) for e (mu) • 1.5 sigma agreement with FEWZ + MSTW08 NNLO total cross section Jeffrey Berryhill, Fermilab -- QCD@LHC Workshop August 20 2012

  12. W and Z Cross-Section Ratios@8 TeV • W/Z ratio: • acc. ratio theory error 2% (2.5%) for e (mu) • Exp. error 3.9% (1.7%) for e (mu) • 1.5 sigma agreement with FEWZ + MSTW08 NNLO total cross section Jeffrey Berryhill, Fermilab -- QCD@LHC Workshop August 20 2012

  13. W and Z Cross-Section Prospects • Not likely to add more data. • Finish estimation of total (and fiducial) cross sections, ratios, and 8/7 double ratios, in context of each PDF family. • 8/7 ratios: • Cross sections: Lumi error does *not* cancel, ~8 % precision for 8/7 ratio • Cross section ratios: if everything but stat cancels, 1% precision possible for 8/7 double ratio • (W/Z)8/(W/Z)7: 1.01 +/- 0.01 (stat), expect 1.03 from FEWZ+MSTW • (W+/W-)8/(W+/W-)7: 0.98 +/- 0.01 (stat), expect 0.99 from FEWZ+MSTW • PDF families disagree in double ratio prediction at ~1% level Jeffrey Berryhill, Fermilab -- QCD@LHC Workshop August 20 2012

  14. W Electron Asymmetry @ 7 TeV • In pp, charge asymmetric CMS-fiducial W production at 10-20%, increasing with lepton |eta| Sensitive to u/d valence and sea at x = 0.001 to 0.1 36/pb measurement with 2010 data already had constraining power Jeffrey Berryhill, Fermilab -- QCD@LHC Workshop August 20 2012

  15. W Electron Asymmetry @ 7 TeV • For the first 840 /pb of 2011, could trigger electrons inclusively down to 35 GeV • Repeat technique of W+/- cross section in 11 bins of 0.2 in |eta|, range 0 to 2.2 • Rel. stat. error/bin of better than 3% CERN-PH-EP-2012-151 Jeffrey Berryhill, Fermilab -- QCD@LHC Workshop August 20 2012

  16. W Electron Asymmetry @ 7 TeV • Dominant error is statistics for e+/e- efficiency ratio measurement in Z’s(~0.5% abs. error) • Agreement with CT/HERA/NNPDF • Disagreement with MSTW2008NLO at low |eta| (subsequently improved) • Full covariance presented Jeffrey Berryhill, Fermilab -- QCD@LHC Workshop August 20 2012

  17. W Muon Asymmetry @ 7 TeV CMS-PAS-EWK-11-005 • For first 234 /pb of 2011, could trigger non-isolated muons down to 25 GeV and |eta| < 2.4 • Precision comparable to electron result (better acc*eff for W’s and Z control samples), similar trends of PDF agreement • Already systematics limited by equal parts momentum scale, eff. ratio, signal model Jeffrey Berryhill, Fermilab -- QCD@LHC Workshop August 20 2012

  18. W asymmetry prospects MSTW, PDF4LHC May 2012 • Impact on next-gen PDFs being assessed • Another factor of 2 in precision is feasible, but alignment/energy scale is a limiting factor going forward. • Full 2011 result for muons in progress • W boson rapidity asymmetry being explored • Asym. with/without jets or vs. PT: additional constraining power? Jeffrey Berryhill, Fermilab -- QCD@LHC Workshop August 20 2012

  19. Drell-Yan Differential Cross Section CMS-PAS-EWK-11-007 • With full 2011 data set, 1D differential Drell-Yan cross section vs. mass measured in electrons and muons for M=20-1500 GeV. • Mu pair analysis: • Mu PT > 14,9 GeV, |eta(mu)| < 2.4 • QCD background estimated from SS and non-isolated mu pairs, tt from emu data. • NNLO corrections important at low mass (we select mostly boosted pairs here) • FSR effects unfolded Good agreement of total Born level cross section with FEWZ+MSTW Jeffrey Berryhill, Fermilab -- QCD@LHC Workshop August 20 2012

  20. Drell-Yan Differential Cross Section • e pair analysis: • E PT > 20,10 GeV, |eta(e)| < 2.5 • QCD background estimated from e+anti-select e convolved with fake rate Good agreement of total Born level cross section with FEWZ+MSTW Jeffrey Berryhill, Fermilab -- QCD@LHC Workshop August 20 2012

  21. Drell-Yan Differential Cross Section • For mu pairs, double-differential (M, y) cross section obtained (detector fiducial cross section, normalized to NZ) • Six bins in M and varying bins in y. • Low-mass bins (20-30, 30-45): NNLO important here, preliminary disagreement with POWHEG, FEWZ and data observed (FEWZ theory value/errors being revisited) Jeffrey Berryhill, Fermilab -- QCD@LHC Workshop August 20 2012

  22. Drell-Yan Differential Cross Section • On-peak bins (45-60, 60-120): excellent agreement with POWHEG and FEWZ • 60-120 (aka “Z rapidity”) systematics limited, consistent with 2010 result Jeffrey Berryhill, Fermilab -- QCD@LHC Workshop August 20 2012

  23. Drell-Yan Differential Cross Section • High mass bins (120-200, 200-1500): excellent agreement with FEWZ, statistics limited Jeffrey Berryhill, Fermilab -- QCD@LHC Workshop August 20 2012

  24. Drell-Yan Cross Section Prospects • Final 2011 result nearing completion • Combine e and mu for 1D cross section • Add e for 2D cross section • Compute full covariance for 1D and 2D • Field testing PDF impact • 8 TeV data will extend the mass reach and improve statistics at high mass • Improving on on-peak or low-mass will require improved detector/FSR understanding (alignment/scale, FSR unfolding) Jeffrey Berryhill, Fermilab -- QCD@LHC Workshop August 20 2012

  25. Drell-Yan Differential AFB @7 TeV • Angular production asymmetries sensitive to weak mixing angle (on-peak) and gamma-Z (or Z-Z’ or Z-new physics) interference off-peak • In pp, quark direction only weakly correlated with Z longitudinal boost, with stronger correlation at high rapidity. Observed angular distributions (cos theta*) have diluted asymmetries relative to “MC-parton-truth” level. • Detector acceptance also dilutes observed AFB • Measure AFB • in fiducial acceptance • Corrected for efficiency and FSR (unfolded to Born level) • As a function of mass, in four slices of y (0-1, 1-1.25, 1.25-1.5, 1.5-2.4) • Compared with Born-level POWHEG+CT10 CERN-PH-EP-2012-187 Jeffrey Berryhill, Fermilab -- QCD@LHC Workshop August 20 2012

  26. Drell-Yan Differential AFB @7 TeV • Dilepton selection: • PT > 20 GeV, |eta|< 2.4 • 10 mass bins from 40 to 2000 GeV • Efficiency corrected • Born-level unfolded • Systematics limited below~150 GeV (alignment/scale/FSR unfolding) • Stat-limited above • Excellent agreement with POWHEG+CT10 Jeffrey Berryhill, Fermilab -- QCD@LHC Workshop August 20 2012

  27. Drell-Yan AFB Prospects • Other differential angular coefficients will be studied • Off-peak precision will improve with 8 TeV data set(esp. above 200 GeV) and test electroweak interactions at highest masses. Electroweak corrections important at ~TeV? • On-peak AFB and weak mixing angle already systematics limited by alignment/energy scale, pQCD, and PDF effects • 50-100 /fb required for stat error of weak mixing angle to approach LEP+SLD precision -> need full 14 TeV run • Not constraining for PDFs for foreseeable future Jeffrey Berryhill, Fermilab -- QCD@LHC Workshop August 20 2012

  28. Conclusions • LHC electroweak boson measurements have had a strong impact on understanding of PDFs and pQCD (required for any future LHC insight on MW or sin2thetaW) • On-peak/low mass, detector systematics (esp. lepton momentum/energy) dominating total error and impeding progress • At highest mass, DY will always be worth pursuing • Topics pursued but not mentioned: • Z rapidity using forward electrons • Strange quark PDF fits • Z multiply-diff angular distributions • Z PT • W PT (@low lumi) Jeffrey Berryhill, Fermilab -- QCD@LHC Workshop August 20 2012

  29. Detector-level distributions of Drell-Yan mass spectrum, vs. FEWZ-corrected POWHEG Jeffrey Berryhill, Fermilab -- QCD@LHC Workshop August 20 2012

  30. FSR unfolding of the 1D Drell-Yan spectrum Jeffrey Berryhill, Fermilab -- QCD@LHC Workshop August 20 2012

  31. Drell-Yan efficiency, acceptance and eff*acc vs. mass Jeffrey Berryhill, Fermilab -- QCD@LHC Workshop August 20 2012

  32. Detector-level rapidity distribution of low-mass Drell-Yan dimuons, compared with FEWZ-corrected POWHEG Jeffrey Berryhill, Fermilab -- QCD@LHC Workshop August 20 2012

  33. Detector-level rapidity distribution of on-peak Drell-Yan dimuons, compared with FEWZ-corrected POWHEG Jeffrey Berryhill, Fermilab -- QCD@LHC Workshop August 20 2012

  34. Detector-level rapidity distribution of high-mass Drell-Yan dimuons, compared with FEWZ-corrected POWHEG Jeffrey Berryhill, Fermilab -- QCD@LHC Workshop August 20 2012

  35. Jeffrey Berryhill, Fermilab -- QCD@LHC Workshop August 20 2012

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