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

2. Boundary Conditions Assume that –Physics of the first year = Physics at 1 fb -1 –√s = 14 TeV for instantaneous luminosities of 10 31 - 10 33 cm -2 s -1 This talks is focused on W/Z/Drell Yan Physics –Jet (and  ) 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 Provisional Reach 10 31 Running at 75 ns L~ 10 32 cm -2 s -1 ~ 3 months of running +some optimism ~ 1 fb -1

4. Cross sections and rates at 10 32 cm -2 s -1 At Luminosity ( 10 32 cm -2 s -1 ) SM Higgs (115 GeV/c 2 ):  0.001 Hz t t production:  0.1 Hz W   :  1 Hz bb production:  10 4 Hz Inelastic:  10 7 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 2X10 33 cm -2 s -1 Thresholds will be much lower at startup… TRIGGER OBJECT THRESHOLD (GeV) RATE (Hz) ISOLATED MUONS1925 DI-MUONS7 (both)5 ISOLATED ELECTRONS2623 ISOLATED DI-ELECTRONS12 (both)1 ISOLATED PHOTONS80 4 ISOLATED DI-PHOTONS30, 20 2 SINGLE JET, 2 JET 3 JET, 4 JET400, 350, 195,80 20 JET + MISSING ENERGY180,803 TAU+ MISSING ENERGY86, 65 (MET)1 INCLUSIVE TAU JETno- DI-TAU JET59 (both)5 ELECTRON + TAU JET19, 451 MUON + TAU JET15,401 B JET + MULTIJETS350,150,5510 OTHERS (pre-scales, calib., etc.)19 TOTAL120

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 p T resolution integrated in  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=10 32 cm -2 s -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. Electrons and photons: calibration with tracks different regions in η ~ 1 fb -1 Important to select tracks with low bremsstrahlung

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, W , Z  ) 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-2006/124 CMS Note-2006/082

13. Z/W  muons Safe definitions of 'hard' muon or track –P t > 20 GeV for Z, 25 GeV for W (well above trigger thresholds) –|  | < 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 M T 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 CMS Note-2006/082

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

15. Total systematics in    ● 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). (CMS, for L ~ fb -1 )

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. W sample:  p t Z sample:  p t ● 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. CMS

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

18. Z/W  Electrons Hard selection aimed to minimal sensitivity to calorimeter uncertainties at startup, useful for luminosity monitoring –E t > 20 GeV for Z, 29 GeV for W (well above trigger thresholds) –|  | < 1.4 (barrel), 1.6< |  | <2.4 (endcap) (avoid overlap) –Consistency with e.m. shower in |  | (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 CMS Note-2006/124

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 (R I ) is applied. Only good tracks are considered: –Associated to the Primary Vertex –P T of the Leading Track (i.e. highest p T track) must exceed a few GeV/c –Leading Track must be found inside the Matching cone R M : calo jet - leading track matching cone p T LT : cut on pT of the leading track in matching cone R S : signal cone around leading track R I : isolation cone (around jet axis or leading track) p T i : 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. CMS Tracker Isolation: tau jets and QCD jets efficiency Cuts used: 8 hits per track, Norm. Chi 2 < 10 P t LT > 6 GeV/c, R M = 0.1, R I = 0.2-0.5, P T I > 1 GeV, |Dz| < 2mm Single Tau (30<E T <150 GeV) QCD jets 50<E T <170 GeV In the order of decreasing efficiency symbols correspond to decreasing MC E T intervals

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

25. 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 (E T (jet) > 50 GeV) Number of W+jets events for L = 1 fb -1 sizeable top background in W+jet channels Z + 4 jets already observable with L ~ 100 pb -1 Number of Z+jets events for L = 1 fb -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. 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. CMS Note-2006/099

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

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

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 1)CMS preparing effort for PDF measurements. Suggestions for interesting observables most welcome. 2) Luminosity measurement. Would be useful to have agreed recipe for phase space cuts where PDF rock solid from other experiments. 3) Electroweak corrections for high p t W,Z and for high mass DY very relevant. Ideas to test them separately from QCD effects. 4)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 Pt vs the closest b tagged jet b-jets c-jets uds-jets CMS Note-2006/077

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