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EW Corrections for CMS Z and Drell-Yan M easurements

EW Corrections for CMS Z and Drell-Yan M easurements. Dimitri Bourilkov University of Florida For the CMS Collaboration Working Group on Electroweak precision measurements at the LHC, and PDF4LHC, CERN, October 9, 2012 . Introduction.

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EW Corrections for CMS Z and Drell-Yan M easurements

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  1. EW Corrections forCMS Z and Drell-Yan Measurements DimitriBourilkov University of Florida For the CMS Collaboration Working Group on Electroweak precision measurements at the LHC, and PDF4LHC, CERN, October 9, 2012

  2. Introduction • Electroweak (EW) corrections around the Z peak and for high mass Drell-Yan • Review of CMS Z (W) and Drell-Yan results • Reached/expected experimental precision  control QCD and EW corrections in precision calculations • Calculations with FEWZ3.1: a tool to calculate simultaneously QCD corrections up to NNLO and EW corrections at NLO: • O(αs2) + O(αEW) for Z/γ∗→ ℓℓ (arXiv:1208.5967) • MRST2004QED PDF used (includes QED corrections to DGLAP evolution of PDFs) EW Corrections in Z and DY

  3. Electroweak Corrections for Z/* • Non-resonant contributions from s-channel * exchange • Gauge invariance of photonic O() corrections  splitting in QED (not discussed here) and pure weak O() corrections: • Near Z peak: • QED corrections described by radiator functions • Weak corrections absorbed in line shape parameters • Invariant mass Ml+l- directly related to off-shellness of Z boson • EW corrections depend on the scales probed; important for mass determinations (W), for high invariant masses of Z/* EW Corrections in Z and DY

  4. Electroweak Corrections for Z/* • At the TeV scale, large and significant impact of pure weak corrections; factors like Sudakov logs (from vertex and box corrections) modify the inclusive cross sections: • ~ W ln2(2/MW2) • At  = 1 TeV this is ~ 25 * W • Effects ~ 10 % in the TeV region • Data in 2012 @ TeV will start probing at this level of precision EW Corrections in Z and DY

  5. Early Studies • LHC SM workshop • “SM Physics (and more) at the LHC” CERN Yellow Report 2000-004 http://arxiv.org/abs/hep-ph/0003275 • Studies for 14 TeV • Highlighted the importance of pure EW corrections EW Corrections in Z and DY

  6. Z Cross Sections @ 8 TeV https://cdsweb.cern.ch/record/1460098 • Dedicated low pile-up run at 8 TeV • Pair mass 60-120 GeV • Lepton PT > 25 GeV, || < 2.1 for muons, || < 2.5 for electrons (excluding barrel-endcap transition) • Lineshape described well by POWHEG+PYTHIA EW Corrections in Z and DY

  7. Inclusive Z Cross Sections @ 8 TeV 10710 Z events, very low background Experimental uncertainties 2.8-1.9% for ee,  Systematics dominated by lumi (4.4 %) and theory uncertainty, mainly acceptance (2.6-1.9%) EW corrections smaller EW Corrections in Z and DY

  8. W/Z Ratios and  @ 8 TeV • Satisfactory agreement with NNLO predictions: FEWZ + MSTW2008 EW Corrections in Z and DY

  9. W/Z Ratios and  @ 8 TeV Only PDF uncertainties are included in the theory uncertainties EW Corrections in Z and DY

  10. Drell-Yan Mass Spectrum https://cdsweb.cern.ch/record/1439026 • Lepton pairs with PT > 14,9 GeV , > 20 GeV ee • FSR effects unfolded (“Born” leptons, before QED FSR) • NNLO predictions with FEWZ+MSTW08 • NNLO effects at low mass important EW Corrections in Z and DY

  11. Drell-Yan Double Diff. Cross Section • Double differential cross section in M & Y • In CMS acceptance, for , normalized to Z cross section • 6 bins in M, 24 or 12 bins in |Y| • Low mass needs more work, improve theory predictions • 45-60 and 60-120 GeV: excellent agreement with POWHEG and FEWZ • Z peak bin systematics limited • 120-200 and 200-1500 GeV: good agreement with POWHEG and FEWZ • High mass bin statistics limited; will improve with 8 TeV data EW Corrections in Z and DY

  12. Forward-backward Asymmetry http://cdsweb.cern.ch/record/1430637 • POWHEG+PYTHIA+CT10 • Forward-backward asymmetry will become sensitive to EW corrections EW Corrections in Z and DY

  13. Z PT • Z PT spectrum at 7 TeV http://arxiv.org/abs/1110.4973 • Theory predictions: QCD at NNLO • New physics can show up in the tail EW Corrections in Z and DY

  14. Z’ Search @ 7 TeV http://lanl.arxiv.org/abs/1206.1849 • Accumulating events > 1 TeV • Entering the Sudakov zone EW Corrections in Z and DY

  15. Z’ Search @ 8 TeV https://cdsweb.cern.ch/record/1461216 • Expanding the reach above 1 TeV • By the end of the 2012 run the statistical precision will start to probe EW corrections EW Corrections in Z and DY

  16. EW Corrections with FEWZ3.1 • Calculations with FEWZ_3.1.b2 (goodbackward compatibility with FEWZ2): a tool to calculate simultaneously QCD corrections up to NNLO and EW corrections up to NLO for Z and DY production • Results for QCD NLO  EW NLO shown • MRST2004QED PDF used • G scheme to “minimize” higher order EW corrections • “Standard” input file for muons • Roughly in CMS acceptance: • PT > 25 GeV, || < 2.4 for both leptons EW Corrections in Z and DY

  17. EW Corrections with FEWZ3.1: Mass EW Corrections in Z and DY

  18. EW Corrections with FEWZ3.1: Afb EW Corrections in Z and DY

  19. EW Corrections with FEWZ3.1: Y EW Corrections in Z and DY

  20. EW Corrections with FEWZ3.1: PT EW Corrections in Z and DY

  21. Outlook • EW corrections will grow in importance for the complete 2012 data set • New tools e.g. FEWZ3.1 (beta) available to study these effects • First round of calculations looks promising • Refine the studies: • QCD NNLO  EW NLO • Realistic experimental cuts for electrons and muons EW Corrections in Z and DY

  22. Backup Slides EW Corrections in Z and DY

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