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EW Corrections for Z and High Mass Drell-Yan Measurements in CMS

EW Corrections for Z and High Mass Drell-Yan Measurements in CMS. Dimitri Bourilkov University of Florida For the CMS Collaboration Working Group on Electroweak Precision M easurements at the LHC , CERN , February 18, 2013. Introduction.

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EW Corrections for Z and High Mass Drell-Yan Measurements in CMS

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  1. EW Corrections for Z and High Mass Drell-Yan Measurements in CMS DimitriBourilkov University of Florida For the CMS Collaboration Working Group on Electroweak Precision Measurements at the LHC, CERN, February 18, 2013

  2. Introduction • Electroweak (EW) corrections around the Z peak and for high mass Drell-Yan • Reached/expected experimental precision requires  good control of QCD and EW corrections in precision calculations • Study the effects of EW corrections for the di-electron and di-muon channels in the CMS acceptance: • Mass • Afb • Rapidity • PT EW Corrections in DY

  3. FEWZ3.1 Calculations • Calculations with FEWZ3.1 @ 8 TeV: 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) • G scheme to “minimize” higher order EW corrections; study scheme dependence • “Standard” CMS cuts for electrons, muons • Roughly in CMS acceptance: • PT > 25 GeV, || < 2.4 for both leptons • “dressed” electrons: R < 0.1 for recombination (ECAL) • “bare” muons: no recombination EW Corrections in DY

  4. 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 DY

  5. FEWZ3.1 EW Corrections: Z Mass electronsmuons EW Corrections in DY

  6. FEWZ3.1 EW Corrections: High Mass electronsmuons EW Corrections in DY

  7. Scheme Dependence • Compared ratios of cross sections for G and Z schemes • Differences are small at EW NLO: • ~ +- 2 % at Z, ~ 2% at TeV EW Corrections in Z and DY

  8. Double Counting of FSR electronsmuons • PYTHIA and POWHEG+PYTHIA already include FSR effects, which lower the observed di-lepton invariant mass • FEWZ also calculates these effects and adds additional terms; double counting? EW Corrections in Z and DY

  9. FEWZ3.1 EW Corrections: Afb@ Z electronsmuons EW Corrections in DY

  10. FEWZ3.1 EW Corrections: Afb@ TeV electronsmuons EW Corrections in DY

  11. FEWZ3.1 EW Corrections: Y @ Z electronsmuons EW Corrections in DY

  12. FEWZ3.1 EW Corrections: Y @ TeV electronsmuons EW Corrections in DY

  13. FEWZ3.1 EW Corrections: PT @ Z electronsmuons EW Corrections in DY

  14. FEWZ3.1 EW Corrections: PT @ TeV electronsmuons EW Corrections in DY

  15. Outlook • EW corrections will grow in importance for the complete 2012 data set • New tools e.g. FEWZ3 available to study these effects • First round of calculations at NLO looks promising • Refine the studies: • QCD NNLO +EW NLO @ 8 TeV ongoing • Realistic experimental cuts for electrons and muons • Avoid double counting EW Corrections in DY

  16. Backup Slides EW Corrections in Z and DY

  17. 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 DY

  18. 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 DY

  19. 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 DY

  20. 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 DY

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

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

  23. 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 DY

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