A measurement of the ratio of the W and Z cross sections with exactly one associated jet in pp collisions at √s=7 TeV with ATLAS

The MIT Faculty has made this article openly available. Please share how this access benefits you. Your story matters. A measurement of the ratio of the W and Z cross sections with exactly one associated jet in pp collisions at √ s = 7 TeV with ATLAS ✩ .ATLAS Collaboration a r t i c l e i n f o a b s t r a c t The ratio of production cross sections of the W and Z bosons with exactly one associated jet is presented as a function of jet transverse momentum threshold. The measurement has been designed to maximise cancellation of experimental and theoretical uncertainties, and is reported both within a particle-level kinematic range corresponding to the detector acceptance and as a total cross-section ratio. Results are obtained with the ATLAS detector at the LHC in pp collisions at a centre-of-mass energy of 7 TeV using an integrated luminosity of 33 pb −1. The results are compared with perturbative leading-order, leading-log, and next-to-leading-order QCD predictions, and are found to agree within experimental and theoretical uncertainties. The ratio is measured for events with a single jet with p T > 30 GeV to be 8.73 ± 0.30(stat) ± 0.40(syst) in the electron channel, and 8.49 ± 0.23(stat) ± 0.33(syst) in the muon channel. Measurements of vector bosons V where V = W or Z produced in association with one or more jets (V + jet) [1–4] provide an important test of the Standard Model (SM) description of the strong interaction in perturbative quantum chromodynamics (QCD). This is particularly important in the kinematic region accessible at the LHC in order to understand the physics at or above the electroweak symmetry-breaking scale. Production of vector bosons is also a significant source of background for studies of other SM processes, including studies of top quark properties, searches for the Higgs boson, as well as in many searches for physics beyond the Standard Model. Measurements of the kinematic properties and dynamics of V + jet processes and comparisons to theoretical predictions are therefore of significant interest. Individual measurements of kine-matic observables in W + jet [4] and Z + jet events are limited by systematic uncertainties common to both. Measurement of the ratio was first proposed in Ref. [5] to exploit the cancellation of theoretical and experimental uncertainties, therefore building the foundations for a high precision test of the Standard Model. …