A measurement of the cross section for top quark-antiquark (t¯t) pairs produced
in association with a photon in proton-proton collisions at √
s = 8 TeV is presented.
The analysis uses data collected with the CMS detector at the LHC, corresponding to an
integrated luminosity of 19.7 fb1
. The signal is defined as the production of a t¯t pair in
association with a photon having a transverse energy larger than 25 GeV and an absolute
pseudorapidity smaller than 1.44. The measurement is performed in the fiducial phase space
corresponding to the semileptonic decay chain of the t¯t pair, and the cross section is measured
relative to the inclusive t¯t pair production cross section. The fiducial cross section for
associated t¯t pair and photon production is found to be 127±27 (stat+syst) fb per semileptonic
final state. The measured value is in agreement with the theoretical prediction.