02 09 07 7 v 1 2 7 Se p 20 02 1 W Boson Cross Section and Decay Properties at the Tevatron

We present the first measurements of σ(p¯ p → W → ℓν) and σ(p¯ p → Z → ℓℓ) at √ s = 1.96 TeV, along with new measurements of W angular-decay distributions in p¯ p collisions at √ s = 1.8 TeV. W and Z boson production cross-section measurements in p¯ p collisions are a test of the consistency of Standard-Model couplings, constrain proton parton distribution functions, and provide information on higher-order QCD corrections. They also test the mettle of an experiment, as the measurements require good understanding of detection efficiencies, backgrounds, and lumi-nosity. If experimental uncertainties are small, and the cross sections can be well-estimated from theory, the boson production rates can be interpreted as a measure of luminosity, and can also be used to normalize measurements of other production cross sections. Finally, W and Z bosons provide a path to the physics of Run II at the Teva-tron, where many signatures of top-quark and Higgs-boson production can include these bosons. At the Tevatron, protons and antiprotons collide at a center-of-mass energy of 1.96 TeV. A W boson appears in the detector as a high-momentum lepton and large missing energy due to the undetected neutrino. As the z component of p ν is unmeasured, all quantites are measured in the transverse plane. A Z boson appears as two high-momentum opposite-signed leptons with an invariant mass around 90 GeV. The cross section can be expressed as σ · B = N obs − N bg Aǫ Ldt , (1) where N obs is the number of observed boson events, N bg is the estimated number of background events, A is the kinematic and geometric acceptance, ǫ is the total efficiency, and Ldt is the integrated luminosity. The lepton plus missing transverse-energy sample can be accounted for by W → ℓν, Z → ℓℓ, W → τ ν, QCD jets (fake leptons), and (for muons) cosmic rays, as illustrated in Figure 1. CDF measures the W cross section in the electron and muon decay channels, and D0 does so in the electron channel. (CDF also looks at mono-jet events with large missing energy, and sees an enhancement in the number of jets with one and three charged tracks, evidence for W → τ ν decays .) The inputs and results for the cross-section measurements are given in Table 1. The measurements are systematics-limited, with the overall uncertainty typically dominated by …