Measurement of the production cross section of Wgamma and Zgamma at sqrt(s) = 7 TeV with the ATLAS Detector

We present measurements of high energy photons produced in associated with either a W or Z boson in pp collisions at √s = 7 TeV. The analysis uses the full data sample (∼35 pb−1) collected by the ATLAS experiment in 2010. Events with W and Z bosons decaying into high PT electrons and muons are required in addition to have a photon with ET > 15 GeV located outside a cone of radius 0.7 in η - φ space centered on the lepton(s) from the boson decay.Atotalof95(97)p+p→eνγ+X(p+p→μνγ+X)and25(23)p+p → e+e−γ + X ( p+ p → μ+μ−γ + X) event candidates are selected. Residual background of p + p → lνγ + X process in the signal candidates sample is estimated using data-driven techniques based on isolation energy in a narrow cone around the photon candidate. The measured production cross sections, together with the kinematic distributions of the leptons and photons in data signal candidates events, are found to agree with the Standard Model predictions with next-to-leading-order O(α αs )corrections.