Using data corresponding to 6.0 fb-1 of p anti-p collisions
at s**(1/2) = 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, tt-bar gamma. The events are selected by looking for a
lepton (งค) , a photon (gamma), 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). The tt-bar 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 tt-bar
gamma candidate sample we measure the production cross section of tt-bar
(sigma_{tt-bar}, and the ratio of cross sections of the two samples.
Control samples in the dilepton+photon and lepton+photon+E(t), channels
are constructed to aid in decay product identification and background
measurements. We observe 30 tt-bar gamma candidate events compared to
the standard model expectation of 26.9 +/- 3.4 events. We measure the
tt-bar gamma cross section (sigma_{tt-bar gamma}) to be 0.18 +/- 0.08 pb,
and the ratio of sigma_{tt-bar gamma) to sigma_{tt-bar} to be 0.024 +/-
0.009. Assuming no tt-bar 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.
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Updated: Monday, 2011 September 19 12:06:22 CDT automatically from input from "Carol Picciolo"