Book Description

Using data corresponding to 6.0 fb−1 of p{bar p} collisions at √s = 1.96 TeV collected by the CDF II detector, we present a cross section measurement of top-quark pair production with an additional radiated photon, t{bar t}[gamma]. The events are selected by looking for a lepton (l), a photon ([gamma]), significant transverse momentum imbalance (E{sub T}), large total transverse energy, and three or more jets, with at least one identified as containing a b quark (b). The t{bar t}[gamma] sample requires the photon to have 10 GeV or more of transverse energy, and to be in the central region. Using an event selection optimized for the t{bar t}[gamma] candidate sample we measure the production cross section of t{bar t} ([sigma]{sub t{bar t}}), and the ratio of cross sections of the two samples. Control samples in the dilepton+photon and lepton+photon+E{sub T}, channels are constructed to aid in decay product identification and background measurements. We observe 30 t{bar t}[gamma] candidate events compared to the standard model expectation of 26.9 ± 3.4 events. We measure the t{bar t}[gamma] cross section ([sigma]{sub t{bar t}}) to be 0.18 ± 0.08 pb, and the ratio of [sigma]{sub t{bar t}[gamma]} to [sigma]{sub t{bar t}} to be 0.024 ± 0.009. Assuming no t{bar t}[gamma] production, we observe a probability of 0.0015 of the background events alone producing 30 events or more, corresponding to 3.0 standard deviations.