W and Z production: cross section and asymmetries at the LHC

1. W and Z production: cross section and asymmetries at the LHC Monika Wielers RAL On behalf of ATLAS and CMS

2. W and Z production • LHC is W/Z factory • (Wl) ~ 15nb  107 events in L dt = 1 fb-1 • (Zll) ~ 1.5nb  106 events in L dt = 1 fb-1 • Foreseen measurements • Measurement of W/Z inclusive cross section as well as W/Z+jet • Constraining PDF’s • Measurement of sin2W • Measurement of W mass and width (see talk by M. Malberti later this morning) • Measurement of gauge boson pair production(see talk by Z. Zhao tomorrow afternoon) • Measurement of triple gauge couplings • Understanding detector and performance • In situ calibration of EM calorimeter using Zee • Alignment via Z • Extraction of trigger and offline lepton identification efficiencies • Measurement of luminosity M. Wielers (RAL)

3. ATLAS Detector • Magnetic Field • 2T solenoid plus air core • toroid • Inner Detector • s/pT ~ 0.05% pT(GeV)0.1% • in |h| < 2.5 • Calorimetry • Covers |h| < 5.0 • EM Calorimetry • s/E ~ 10%/√E(GeV)1% • |h| < 3.2 with fine granularity • in |h| < 2.5 • Hadronic Calorimetry • s/E ~ 50%/√E(GeV)3% in • ||<3 • Muon Spectrometer • s/pT ~ 2-7 % in |h| < 2.7 • Precision physics in |h|<2.5 M. Wielers (RAL)

4. The CMS Detector • Magnetic Field • 4T solenoid • Inner Detector • s/pT ~ 0.015% ·pT(GeV)in • |h| < 2.5 • Calorimetry • Covers |h| < 5.0 • EM Calorimetry • s/E ~ 5%/√E(GeV)2% in • |h| < 3.2 • Hadronic Calorimetry • s/E ~ 65%/√E(GeV)5% in • ||<3 • Muon Spectrometer • s/pT ~ 0.05 ·pT(TeV) • (tracking+muon) • Covers |h| < 3.0 M. Wielers (RAL)

5. Status of ATLAS/CMS M. Wielers (RAL)

6. New LHC machine schedule • Machine milestones • Initial operation will be with 450 GeV beam energy with a static machine (no ramp, no squeeze) to debug machine and detectors • Afterwards shut-down (~3 months) during which the remaining machine sectors will be commissioned without beam to full energy (7 TeV) • In spring 2008 LHC will be brought into operation for the first physics run at 7+7 TeV, with the aim to integrate substantial luminosity by the end of 2008 • SPC stressed that the goal should be several fb-1 integrated luminosity at the end of 2008 M. Wielers (RAL)

7. W and Z production at the LHC xf(x,Q2) |h|<2.5 x Q2 (GeV) x • Large W/Z cross section at LHC • (Wl) ~ 15nb • (Zll) ~ 1.5nb • Main (LO) contribution • Sea-sea parton interactions at low-x will dominate • At Q2~M2W/Z sea driven by the g  qq contribution • gluon far less precisely determined for all x values M. Wielers (RAL)

8. Measurement of W / Z cross-sections Cross section measurement accuracies for CMS for L =1fb-1 • s(Zmm + X) = 1160 ± 1.5 (stat) ± 27 (syst)  116 (lumi) pb • s(Wmn + X) = 14700 ± 6 (stat) ± 485 (syst)  1470 (lumi) pb Systematics theory dominated (acceptance). At a later stage these processes can be used as luminosity monitor (Error on luminosity: ~5%) W CMS We ATLAS M. Wielers (RAL)

9. We rapidity distributions e-rapidity e+ rapidity CTEQ61 CTEQ61 MRST02 MRST02 ZEUS02 ZEUS02 ds(We)/dy Generated Generated y ds(We)/dy Reconstructed Reconstructed y • At LHC experimental uncertainty dominated by systematics • Theoretical uncertainties, dominated by PDFs • Exp. uncertainty sufficiently small to distinguish between different PDF sets • PDF error sensitive to W→e rapidity distribution • PDF uncertainties only slightly degraded after detector simulation and selection cuts M. Wielers (RAL)

10. PDF constraining potential of ATLAS ZEUS-PDFBEFORE including W data e+CTEQ6.1 pseudo-data Include ATLAS W Rapidity “pseudo-data” in global PDF Fits Simulate real experimental conditions: Generate 1M “data” sample with CTEQ6.1 PDF through ATLFAST detector simulation and then include this pseudo-data (with imposed 4% error) in the global ZEUS PDF fit (with Det.Gen. level correction). ZEUS-PDFAFTER including W data ds/d (nb) e+CTEQ6.1 pseudo-data |h| |h| low-x gluon shape parameter λ, xg(x) ~ x –λ: BEFORE λ = -0.199 ± 0.046 AFTER λ = -0.186 ± 0.027 41% error reduction (after few days of LHC Running atL=1033cm-2s-1) Normalisation free  independent of luminosity M. Wielers (RAL)

11. High-Mass Lepton pair Production # events m(ll) GeV • Important benchmark process • Deviations from SM cross section indicate new physics ds/dm() (fb/GeV) Di-lepton mass spectrum m() GeV Systematic error CMS Size of uncertainty m(ll) GeV M. Wielers (RAL)

12. Determination of sin2θW(MZ2) [%] q Q • Measure AFB = b { a - sin2θW( MZ2 ) }, a, b calculated to NLO QED and QCD • Measure AFB with leptons in Z0 DY events. Can fit with Mt to constrain MH • Require pTe > 20 GeV, 85.2 < Mee < 97.2 GeV • For L = 100 fb-1 (ATLAS) • Current error on world average 1.6x10-4 • need small systematic error: • PDF uncertainty, • precise knowledge of lepton acceptance and efficiency • effects of higher order QCD • At LHC no asymmetry wrt beam, assume Qq collision • quark Q direction from y(ll) • measurement at high y(ll) ATLAS y(ee) M. Wielers (RAL)

13. Conclusions • W and Z cross sections important early measurements at LHC • Instrumental systematics on W+Z cross-sections with Ds/s~few % for 1fb-1 • W and Z production will help to understand • Detectors and physics performance • Calibration, alignment, efficiency extraction, optimisation of e/ isolation cuts, etc. • Reduce theoretical errors • Gluon pdf’s measured via W rapidity distributions will reduce significantly the error on gluon shape parameter • Measure sin2qW from Zee decays • Potential for measurement comparable with current limits, requires extending electron coverage at large h M. Wielers (RAL)