Abstract: Using data corresponding to 6.0??fb?1 of p¯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 in the central region with 10 GeV or more of transverse energy t¯t?. The events are selected by looking for a lepton ( ? or ?), a photon (?), significant transverse momentum imbalance (E?T), large total transverse energy, and three or more jets, with at least one identified as containing a b quark (b). Using an event selection optimized for the t¯t? candidate sample, we also measure the cross section of t¯t (?t¯t). We measure the t¯t? cross section (?tt?) to be 0.18±0.08??pb, and the ratio of ?t¯t? to ?t¯t to be 0.024±0.009. We observe a probability of 0.0015 (3.0 standard deviations) of the background (non-t¯t? events alone producing 30 events or more.

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