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W / Z / Drell Yan Physics in the first year of CMS

CTEQ Workshop "Physics at the LHC: Early Challenges“ W.K. Kellogg Biological Station 14 th May 2007. W / Z / Drell Yan Physics in the first year of CMS. Roberto Tenchini INFN – Pisa. Boundary Conditions. Assume that Physics of the first year = Physics at 1 fb -1

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W / Z / Drell Yan Physics in the first year of CMS

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  1. CTEQ Workshop "Physics at the LHC: Early Challenges“ W.K. Kellogg Biological Station 14th May 2007 W / Z / Drell Yan Physics in the first year of CMS Roberto Tenchini INFN – Pisa

  2. Boundary Conditions • Assume that • Physics of the first year = Physics at 1 fb-1 • √s = 14 TeV for instantaneous luminosities of 1031 - 1033 cm-2 s-1 • This talks is focused on W/Z/Drell Yan Physics • Jet (and g) Physics is of paramount importance at startup, see talk of Guenther Dissertori (this morning) Use many results from CMS PTDR and related CMS Notes

  3. 2008 Should look something like… Hardware commissioning to 7 TeV Machine Checkout 1 month Commissioning with beam 2 months Pilot Physics 1 month Reach 1031 Provisional Running at 75 ns L~ 1032 cm-2s-1 ~ 3 months of running +some optimism ~ 1 fb-1

  4. Cross sections and rates at1032 cm-2s-1 • At Luminosity (1032 cm-2 s-1) • SM Higgs (115 GeV/c2): 0.001 Hz • t t production: 0.1 Hz • W l n: 1 Hz • bb production:  104 Hz • Inelastic: 107 Hz • PILEUP: at this luminosity not important • Unless 75 ns running. • Example: • 7x10^32, 25 ns --> 2 PU • 8x10^32, 75 ns --> 5 PU

  5. Typical HLT Trigger tables at 2X1033cm-2 s-1Thresholds will be much lower at startup…

  6. Just a few comments on calibrations with the first data

  7. Momentum measurement with the Tracker : estimates for 100 pb-1 and a few fb-1 pT resolution integrated in h Z peak visible even with the first rough alignments

  8. The plentiful production of W and Z bosons are main tools for Detector Commissioning • Example: CMS Muon System alignment using real tracks • Ten days at L=1032 cm-2s-1 is enough to show misalignment of the order of one fourth of mrad

  9. Electrons and photons: initial intercalibration with jets • The azimuthal symmetry can be exploited for a first intercalibration with inclusive jets • Use the Z->ee to get eta calibration

  10. different regions in η Electrons and photons: calibration with tracks Important to select tracks with low bremsstrahlung ~ 1 fb-1

  11. W / Z / Drell Yan Early Physics • Inclusive W and Z cross section • with muons • with electrons • with taus • Measuring W/Z+n-jets, Zbb, etc. • Multibosons (WZ, ZZ, WW, Wg, Zg) • Leptonic DY

  12. Inclusive production of W and Z • Large W (Z) cross section: ~ 10 nb (1 nb) and clean leptonic signatures • Compare to theo. prediction or assume prediction and use to measure luminosity • New studies from CMS TDR: • Selection W and Z samples with decays into leptons of high purity • Simple criteria • Minimally dependent on calibration uncertainties and limited knowledge of the detector response (i.e. startup oriented). CMS Note-2006/082 CMS Note-2006/124

  13. CMS Note-2006/082 Z/Wmuons • Safe definitions of 'hard' muon or track • Pt > 20 GeV for Z, 25 GeV for W (well above trigger thresholds) • |h| < 2.0 (trigger redundancy and efficiency) • Relaxed muon-tracker matching conditions for one of the muons in Z decays. • No isolation criteria for muons: • Already applied at the High Level Trigger filtering step. • (and also isolation at HLT will be relaxed at startup) • For W measure Transverse Missing Energy (MET), use for MT cut and to suppress top background (event with > 3 jets) (MET-muon angle) • High efficiencies are obtained • About 52 % for the Z • About 40 % for the W

  14. Minimizing uncertainties in Zm CMS CMS Enough lever arm to control and understand systematics

  15. Total systematics in Zmm (CMS, for L ~ fb-1) • 600 events recorded/pb: size of statistical uncertainties ~ systematic uncertainties at L ~ 3 pb-1. • Most of the sources assume a detector understood with L=1 fb-1 => systematics will be a bit larger at start-up, and decrease with time • Theory uncertainties are an interesting field of study by themselves (see next slides).

  16. Studies with MC@NLO • LO -> NLO studies with MC@NLO: used to determine systematic uncertainties on the acceptance (~ 2 %) and to calculate k-factors. CMS CMS Z sample: m pt W sample: m pt • In the long term, once NLO effects are understood, and low pt shapes well reproduced, systematics can be assigned according to NLO vs. NNLO comparisons.

  17. PDF uncertainties (CMS) Z sample W sample Z sample W+ sample

  18. CMS Note-2006/124 Z/WElectrons • Hard selection aimed to minimal sensitivity to calorimeter uncertainties at startup, useful for luminosity monitoring • Et > 20 GeV for Z, 29 GeV for W (well above trigger thresholds) • |h| < 1.4 (barrel), 1.6< |h| <2.4 (endcap) (avoid overlap) • Consistency with e.m. shower in |h| (low sensitivity on bremsstrahlung) • Low associated energy in HCAL (<0.5) • Good match with track from Silicon Tracker • Require electron isolation • For W cut on MT, with MET computed from hard jets only to lower sensitivity to calorimeter noise

  19. CMS PTDR: W and Z selections (electrons) • High efficiencies are obtained • About 57 % for the Z • About 26 % for the W • Comments: • i) W selection requires cutting on the transverse mass: • ii) Lepton isolation should be carefully studied with first data Sensitivity on the jet energy scale Understanding Jets is important Both comments apply to the muon channel, too !

  20. Measure the PDFs with W and Z: to be done in CMS Example W charge asymmetry measurement and PDF sensitivity

  21. CMS: Tau Tagging from Ecal isolation CMS get a signal efficiency of about 80% with a bkg rejection of 5 for QCD jets with pT>80 GeV/c

  22. CMS: Tau reconstruction from Tracker isolation • Isolation based on the number of tracks inside the isolation cone (RI) is applied. • Only good tracks are considered: • Associated to the Primary Vertex • PT of the Leading Track (i.e. highest pT track) must exceed a few GeV/c • Leading Track must be found inside the Matching cone • RM : calo jet - leading track matching cone • pTLT : cut on pT of the leading track in matching cone • RS : signal cone around leading track • RI : isolation cone (around jet axis or leading track) • pTi : cut on pT of tracks in the isolation cone • Dz : cut on the distance between z ip of the leading track and z ip of other tracks considered by algorithm (association with pxl primary vertex at HLT; see later)

  23. Single Tau (30<ET<150 GeV) QCD jets 50<ET<170 GeV CMS Tracker Isolation:tau jets and QCD jets efficiency In the order of decreasing efficiency symbols correspond to decreasing MC ET intervals Cuts used: 8 hits per track, Norm. Chi2 < 10 PtLT > 6 GeV/c, RM = 0.1, RI = 0.2-0.5, PTI > 1 GeV, |Dz| < 2mm

  24. Tau production from W and Z decays at CMS Important benchmark for tau reco CMS Note-2006/074 Interesting to check again BR( W -> tau nu )

  25. Number of W+jets events for L = 1 fb-1 sizeable top background in W+jet channels pp->W/Z + n-jets • Jet must be identified and the QCD background must be eliminated via very stringent lepton isolation cuts Initial study using ALPGEN (ET(jet) > 50 GeV) Number of Z+jets events for L = 1 fb-1 Z + 4 jets already observable with L ~ 100 pb-1

  26. pp->W/Z + n-jets visible cross sections [pb] (= #events seen / pb) This channel is relevant for: • Physics: QCD studies • Reduce jet energy scale uncertainties (via Z + jet) • It is an important background for many new particles searches (looking for leptons and jets)

  27. CMS Note-2006/099 PTDR : Zbb production • Zbb is clearly seen at 30 fb-1, need to design an analysis to detect at 1 fb-1 • Interesting also to measure Zcc, Wbb, etc. • Important bkg for searches, check btag, etc.

  28. Multiboson Production at 1 fb-1 • Important test of background to searches • Check Triple Gauge Couplings # events for 1 fb-1 CMS Note-2006/108

  29. Above the Z peak : Drell Yan events • Example from the m+m- channel Drell-Yan production CMS Systematic error ~ 10%

  30. Additional Heavy Neutral Gauge Bosons (Z’) At 100 pb-1 , 1 TeV Z’ with initial alignment

  31. Conclusions • Inclusive W and Z events are major handles • to understand the apparatus at startup • monitor luminosity • tune MC and backgrounds to New Physics • Interesting studies of W/Z+n-jets, Zbb, Multibosons, High mass DY, already in the first year • CMS developing a program to improve understanding as the luminosity increases

  32. A few subjects for Discussion • CMS preparing effort for PDF measurements. Suggestions for interesting observables most welcome. • Luminosity measurement. Would be useful to have agreed recipe for phase space cuts where PDF rock solid from other experiments. •   Electroweak corrections for high pt W,Z and  for high mass  DY  very relevant. Ideas to test them separately from QCD effects. • Any measurement on W/Z+njet, Zbb, beyond cross section ?

  33. Backup Slides

  34. Measuring the W mass at 1 fb-1 CMS Note-2006/061 The crucial point is to control systematic uncertainties: Use the Z to mimic the W !

  35. Measuring the W mass at 1 fb-1 CMS Note-2006/061

  36. B inclusive production • Selection of inclusive jet+muon • Compute muon Pt vs jet axis • Measurement limited by syst uncertainties already at 1 fb-1 (jet energy scale) . Expect ~ 20% precision • Check agreement between pQCD and experiments b-jets c-jets uds-jets CMS Note-2006/077 Pt vs the closest b tagged jet

  37. Additional Heavy Neutral Gauge Bosons (Z’) CMS Note-2006/062

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