Prospects for Early Measurements of W and Z

Prospects for Early Measurements of W and Z Bosons with CMS at the LHC Jeffrey Berryhill (Fermilab) The CMS Collaboration PANIC ’ 08, Eilat, Israel November 11, 2008 W and Z inclusive cross sections (10 pb-1) W lepton rapidity asymmetry (10, 100 pb-1) Z + bb cross section (100 pb-1)

“Everyone has a plan… Conclusion until they get punched in the face. ” --old boxing maxim

Electroweak Bosons as a Precision Calibration Tool For Standard Model physics: Inclusive cross sections compared against initial 10% precision (lumi) …or estimate parton luminosity itself to ~5% (theory) Cross section ratios estimated at ~1% (PDF) …or further constrain PDFs themselves once ~% precision achieved For detector performance: Commissioning leptons for triggering, reconstruction, and identification for PT from 20 to 60 Ge. V measuring performance at the % level First look at efficacy of missing ET for analysis (real or instrumental) Associated production with jets an ubiquitous background for searches

Inclusive W and Z Production Cross Sections • At 10 -14 Te. V, initiated by an admixture of both valence-sea and sea-sea quark annihilation at HERA-like x (10 -5 to 10 -2) Compared to W, Z @ Tevatron: • Cross section 4 -6 X larger • Acceptance for |hl| < 2. 5 is 2 X better for W, 1 X for Z • 100 k W’s and 10 k Z’s for 10 pb-1@10 Te. V W, Z @CMS W →ln s×BR (pb) N×A/pb-1 1. 96 Te. V pp 2700 2*600 10 Te. V pp 11800 2*6000 14 Te. V pp 17200 2*9000 1. 96 Te. V pp 250 2*80 10 Te. V pp 1200 2*400 14 Te. V pp 1800 2*600 Z→ l l MRST, Eur. Phys. J. C 14 (2000) 133 -145

Z →ee Single electron trigger w/isolation 2 high ET electrons (ET>20. 0 Ge. V, |h| < 2. 5) 70 Ge. V < Μee < 110 Ge. V Track Isolated: Σ(PT/PTe)2<0. 02 in a cone of 0. 6 Electron Id: Had/EM energy (Δη, Δφ) track/cluster matching , σηη shower shape Z→ mm Single muon trigger 2 high PT muons (PT>20. 0 Ge. V, |η|<2. 0) Mμμ > 40 Ge. V Hits from Tracker + Muon Chambers Track Isolated: ΣPT<3 Ge. V in a cone of 0. 3 NOT using precision tracking cuts (e. g. ds) in 10 pb-1 startup era Muon trigger efficiency Trigger, reconstruction, and ID efficiency for single leptons can be measured directly from data with Z → ll “tag and probe” samples Electron trigger efficiency Inclusive W and Z Production Cross Sections : Z Selection

Inclusive W and Z Production Cross Sections: Z results 4600 ee (1. 5% stat), 5300 mm (1. 4% stat) selected Backgrounds < sqrt(S) (i. e. any subtraction error is subleading) Mean lepton efficiencies known to 1% (stat) or better Efficiency corrected signal precision comfortably below 5% (useful for lumi)

W →mn Inclusive W and Z Production Cross Sections: W selection One muon (PT>25. 0 Ge. V, |η|<2. 0) Veto 2 nd muon w/ PT> 20 Ge. V Track Isolated: ΣPT/PTμ < 0. 09, ΔR<0. 3 Acoplanarity and multijet vetos Background is primarily bb dijet and Z →mm Transverse mass separates W signal from bb above ~50 Ge. V Non-isolated muons an unbiased template for background transverse mass Z →mm sample used to describe missing ET → an unbiased template for W signal MT Use simple “four-square” (iso/noniso vs. low/high MT) calculation, or a multi-bin likelihood fit, to extract signal yield from MT.

Inclusive W and Z Production Cross Sections: W selection W →en One electron (ET>30 Ge. V, |h|<2. 5) Veto 2 nd electron w/ ET> 20 Ge. V Tighter Track Isolation: no tracks with PT>1. 5 Ge. V in a cone of ΔR<0. 6 Tighter electron Id QCD background is admixture of bb, light dijet, and photon+jet Non-isolated leptons give unbiased estimator of missing ET for isolated leptons, Z→ ee gives missing ET for W signal Four-square method (iso/noniso vs. low/high missing ET) gives marginally unbiased signal yield Need tight ID/Iso cuts to minimize S/B at expense of S/sqrt(S+B)

Inclusive W and Z Production Cross Sections : W Results 28 k e, 64 k m selected, B/S ~ 25% without missing ET cut, <13% with cut Systematics from QCD background subtraction biases comparable to sqrt(S+B)/S Efficiency corrected signal yield precision ~1% for muons, ~3% for electrons Background rejection from missing ET and lepton ID crucial to performance

W Lepton Rapidity Charge Asymmetry W production in pp collisions is globally charge asymmetric (pp has more ud than du collisions due to valence quark content of p): (W+- W-)/(W+ + W-) = +0. 18 total cross section asymmetry Also differentially charge asymmetric in lepton rapidity due to d/u pdf asymmetry vs. x and V-A decay asymmetry of W For leptons in CMS W acceptance, A varies from +10 to +20% Precision at 1% or less, sampled in several rapidity bins, provides PDF constraint tighter than global fits

W Lepton Rapidity Charge Asymmetry Select same W →mn events as for the inclusive cross section: PT(m) > 25 Ge. V, |h(m)| < 2. 0, MT > 50 Ge. V Muon triggering, reconstruction, and ID asymmetry known to <1% from tagand-probe Major backgrounds (QCD, DY) symmetric, w/uniform dilution (20%) vs. h(m) Detector misalignment/miscalibration biases reduced to 1% by 100 pb-1

W Lepton Rapidity Charge Asymmetry For 20 bins in 0. 1 of eta, differential asymmetry known nearly uniformly to 2%(stat) per bin @10 pb-1, an interesting precision cross check <1%(stat) per bin @100 pb-1 would improve the PDFs Further studies: do electrons help (esp. for |h| > 2. 0)? Can W boson rapidity be measured reliably?

Z + bb Production Cross Section MCFM cross section @NLO is 46 pb, LO diagrams via gg fusion and quark-initiated Z+split g Important background to SM heavy Higgs→ 4 l and light SUSY Higgs searches Jumping off point for W+bb, Z+b, et al. Lepton selection: lepton pairs selected as in the inclusive Z analysis Jet selection: >= 2 jets with corrected ET > 30 Ge. V and |h| < 2. 4 Missing ET > 50 Ge. V veto to reduce top quark background Dilepton mass, no b-tagging

Z + bb Production Cross Section: Selection b-tagging: 2 jets with a good value wrt a simple discriminator (3 D IP significance of 3 rd highest IP sig. track) Remaining background is predominantly top, which is estimated using dilepton mass sidebands b jet signal b-tagging efficiency and udsg mistagging from m+jet control samples, c-mistagging from MC Signal yield corrected for b-tag efficiency and Z+jj, cc backgrounds

Z + bb Production Cross Section : Results 46 Z+bb events selected in 100 pb-1, with top background at 30% level Biggest systematics are btagging efficiency (± 16%), JES (± 8%), lumi (10%), MC model (-10%), missing ET model (7%) Significant but systematics limited signal with 100 pb-1

Conclusion With first 10 pb-1 of pp collision data: W and Z production cross section measured and dominated by luminosity error (~10%) in electron and muon channels. Z counting suitable as ~5% estimator of luminosity, dominated by theory error. W a bit more challenging due to QCD background. Lepton trigger/reconstruction/ID tuned and measured to 1% level With 100 pb-1 of pp collision data: Novel PDF constraints from W asymmetry Abundant W and Z + jets signals, including Z + heavy flavor