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W, Z cross-sections and A FB at LHCb

W, Z cross-sections and A FB at LHCb. Ronan McNulty University College Dublin. PDF4LHC 7.03.2011. Outline. Introduction Preliminary results on W,Z cross-sections and ratios. Potential to measure A FB and requirements from PDFs. EW physics motivation. Partonic Cross-section

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W, Z cross-sections and A FB at LHCb

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  1. W, Z cross-sections and AFB at LHCb Ronan McNulty University College Dublin PDF4LHC 7.03.2011 Ronan McNulty, PDF4LHC, 7.03.2011

  2. Outline • Introduction • Preliminary results on W,Z cross-sections and ratios. • Potential to measure AFB and requirements from PDFs. Ronan McNulty, PDF4LHC, 7.03.2011

  3. EW physics motivation Partonic Cross-section FEWZ NNLO(1%) Hadronic Cross-section PDFs (3-5%) Test the SM at highest energies Check out that DGLAP evolution works (test QCD) Push theory into interesting regions with very soft gluons Ronan McNulty, PDF4LHC, 7.03.2011

  4. 9 8 7 6 5 log10(Q2) [GeV2] 4 3 2 1 0 -1 y: 6 4 2 0 2 4 6 W,Z LHC kinematic region LHCb: Collision between one well understood parton and one unknown or large DGLAP evolved parton. LHCb LHCb -6 -5 -4 -3 -2 -1 0 log10(x) Ronan McNulty, PDF4LHC, 7.03.2011

  5. ~LHCb Effect of PDF uncertainties on cross-sections • Region where the most precise EW tests can be made. • At highest rapidities, PDFs can be constrained. • Experimental statistical error <<1%. • Systematic error likely to be ~1% Z W+ W- Percentage uncertainty on cross-sections due to PDF Ronan McNulty, PDF4LHC, 7.03.2011

  6. But you can do better ! So ratio of Ws is sensitive to d to u ratio. (For LHCb dv/uv) W asymmetry is sensitive to difference in u and d. (For LHCb uv-dv) Ratio of Z to W is almost insensitive to PDFs! Gold plated test of SM at the highest energies Ronan McNulty, PDF4LHC, 7.03.2011

  7. Effect of PDF uncertainties on cross-sections • RWZ precise test of SM everywhere. • Difference in u and d quarks can be significantly improved by all experiments at the LHC. • Going forward, you increasingly constrain the u-valence to d-valence ratio. • Even nicer, most experimental systematics (especially luminosity) cancel in the ratio. (W+-W-)/(W+W-) W+/W- Percentage uncertainty on cross-section ratios due to PDF W/Z Ronan McNulty, PDF4LHC, 7.03.2011

  8. Z Cross-section Measurement at LHCb Ronan McNulty, PDF4LHC, 7.03.2011

  9. 8% of Z within LHCb acceptance 17% (16%) of W+ (W-) within LHCb acceptance Ronan McNulty, PDF4LHC, 7.03.2011

  10. Z: Characteristic signature of two high transverse momentum muons with invariant mass mZ Require two muons: pt>20GeV, 2<η<4.5. 81<M<101 GeV Ronan McNulty, PDF4LHC, 7.03.2011

  11. =1 =1 Z: Characteristic signature of two high transverse momentum muons with invariant mass mZ Require two muons: pt>20GeV, 2<η<4.5. 81<M<101 GeV 16.5 pb-1 To turn into cross-section: Insomuch as possible, take everything from data. Ronan McNulty, PDF4LHC, 7.03.2011

  12. Muon identification efficiency • W=98.2  0.5% • Z=96.5 0.7% Efficiency flat in pT,h,f No evidence for charge bias data simulation truth level Ronan McNulty, PDF4LHC, 7.03.2011

  13. Track Efficiency from Tag and Probe • W+=73  3% • W-= 78  3% • Z = 83  3% (W+/W- differ due to lepton h distribution) Ronan McNulty, PDF4LHC, 7.03.2011 (flat in pT and f)

  14. Tag muon fired trigger Does probe muon fire trigger ? Trigger Efficiency from Tag and Probe eW=0.9*(80.5  1.4)% eZ=0.9*(95.7  0.5)% (Globel cuts: Very large events rejected by trigger) Ronan McNulty, PDF4LHC, 7.03.2011

  15. Z analysis Phase space for measurement Ronan McNulty, PDF4LHC, 7.03.2011

  16. Differential distribution (Z) LHCb preliminary (Requiring both muons have pt>20, 2<η<4.5.) 16.5 pb-1 FEWZ NLO with MSTW2008 PDF Ronan McNulty, PDF4LHC, 7.03.2011

  17. W Cross-section Measurement at LHCb Ronan McNulty, PDF4LHC, 7.03.2011

  18. n W W: One high transverse momentum muon with little else. Background much larger than for Z Require muon pt>20GeV + little activity in ‘rest of event’ Can be found using Z events in data Ronan McNulty, PDF4LHC, 7.03.2011

  19. Selecting W events • pt of muon (>20GeV) • ip significance of muon (<2) • Mass of rest of event (<20 GeV) • Pt of rest of event (<10 GeV) • Charged transverse momentum in cone of 0.5 units of √(Δη)2+(ΔΦ)2 around muon. (<2 GeV) Ronan McNulty, PDF4LHC, 7.03.2011

  20. W analysis LHCb preliminary LHCb preliminary Z in simulation Z data W in simulation Bkg from data using anti-cuts • Z(sim) = W(sim) • Z(data) ~ Z(sim) • Bkg(data) != Z(data) • Data derived: • cuts; • efficiency; • purity. LHCb preliminary LHCb preliminary Ronan McNulty, PDF4LHC, 7.03.2011

  21. W analysis LHCb preliminary 16.5 pb-1 Z (fixed with sim) t (fixed and scaled to W) QCD: fit fraction. (shape from data) W+/-: fit fraction (shape from data) W+ W- and all found from data. Ronan McNulty, PDF4LHC, 7.03.2011

  22. W analysis Phase space for measurement (Measurement as function of lepton rapidity) Ronan McNulty, PDF4LHC, 7.03.2011

  23. W asymmetry 16.5pb-1 Ronan McNulty, PDF4LHC, 7.03.2011

  24. W,Z Summary LHCb preliminary Ronan McNulty, PDF4LHC, 7.03.2011

  25. For the future:Intriguing possibility of a precise measurement of AFB Ronan McNulty, PDF4LHC, 7.03.2011

  26. Current precision on sin2qW Unsatisfactory that two most precise measurements are >3s apart, and that W.A. is marginally consistent with either. Ronan McNulty, PDF4LHC, 7.03.2011

  27. AFB in muon channel at LHC is about 5 times larger than at LEP. But sensitivity coming more from Al rather than Au or Ad Ronan McNulty, PDF4LHC, 7.03.2011

  28. statistical uncertainty with 100fb-1 at 14TeV Measuring AFB in pp->Z->mm ? A0FB=3/4 Am( u Au + d Ad + s As) HORACE (Born level) • LHC Problems: • PDF uncertainties • Which is quark direction? • Going forward helps…. Δ(AFB) for Δsin2q=0.0001 How confident are we: - of theory? - of PDF uncertainties? - of detector systematics? Z rapidity Statistically, a forward detector at high luminosity could measure AFB with better precision than current WA (0.00016). With 50fb-1, AFB measured to 0.0004, sin2qW measured to 0.0001 Ronan McNulty, PDF4LHC, 7.03.2011

  29. Uncertainty due to PDF Uncertainty from PDF (from one PDF set) about the same as statistical uncertainty. With time, this should improve (~ 50%?) For 3<yZ<4 0.0004 AFB calculated MSTW Eigenvector number Ronan McNulty, PDF4LHC, 7.03.2011

  30. Summary • W and Z cross-sections limited by luminosity uncertainty. • Ratios limited by knowledge of background in W sample • For the future: PDFs have an impact on theoretical prediction for AFB Ronan McNulty, PDF4LHC, 7.03.2011

  31. from J.Stirling Ronan McNulty, PDF4LHC, 7.03.2011

  32. Ronan McNulty, PDF4LHC, 7.03.2011

  33. Z->ee Z->tautau Ronan McNulty, PDF4LHC, 7.03.2011

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