We present a measurement of the W + W − production cross section using 184 pb −1 of pp collisions at a center-of-mass energy of 1.96 TeV collected with the Collider Detector at Fermilab. Using the dilepton decay channel W + W − →ℓ + νℓ −ν , where the charged leptons can be either electrons or muons, we find 17 candidate events compared to an expected background of 5.0 +2.2 −0.8 events. The resulting W + W − production cross section measurement of σ(pp → W + W − ) = 14.6 +5.8 −5.1 (stat) +1.8 −3.0 (syst) ± 0.9(lum) pb agrees well with the Standard Model expectation.PACS numbers: 13.38.Be, 14.70.Fm
3The measurement of the W pair production crosssection in pp collisions at √ s = 1.96 TeV provides an important test of the Standard Model. Anomalous W W γ and W W Z triple gauge boson couplings [1], as well as the decays of new particles such as Higgs bosons [2], could result in a rate of W pair production that is larger than the Standard Model cross-section of 12.4±0.8 pb [3]. The first evidence for W pair production was found in pp collisions by the CDF collaboration at √ s = 1.8 TeV [4]. The properties of W pair production have been extensively studied by the LEP collaborations in e + e − collisions up to √ s = 209 GeV [5], and have been shown to be in good agreement with the Standard Model. The DØ experiment has recently reported a measurement of the W pair production cross section at Run II of the Tevatron [6].In this Letter we describe a measurement of the W + W − production cross section in the dilepton decay channel W + W − → ℓ + νℓ −ν (ℓ = e, µ), and compare the event kinematics with Standard Model predictions. The signature for W + W − → ℓ + νℓ −ν events is two high-P T leptons and missing transverse energy, E / T , from the undetected neutrinos [7]. Jets from the hadronization of additional partons in the event due to initial-state radiation may be present. This analysis is based on 184 ± 11 pb −1 of data collected by the upgraded Collider Detector at Fermilab (CDF) during the Tevatron Run II period.The CDF II detector [8] has undergone a major upgrade since the Run I data-taking period. The components relevant to this analysis are briefly described here. The Central Outer Tracker (COT) is a large-radius cylindrical drift chamber with 96 measurement layers organized into alternating axial and ±2 • stereo superlayers [9], and is used to reconstruct the trajectories (tracks) of charged particles and measure their momenta. The COT coverage extends to |η| = 1. A silicon microstrip detector [10,11] provides precise tracking information near the beamline in the region |η| < 2. The entire tracking volume sits inside a 1.4 T magnetic field. Segmented calorimeters, covering the pseudorapidity region |η| < 3.6, surround the tracking system. The central (|η| < 1) and forward (1 < |η| < 3.5) electromagnetic calorimeters are lead-scintillator sampling devices, instrumented with proportional and scintillating strip detectors that measure the position and transverse profile of electromagnetic showers. The hadron calorimete...