Reconstruction of collinear final-state-radiation photons in Z decays to muons in sqrt{s}=7 TeV proton-proton collisions.

This note presents a method for including the collinear final-state-radiation photons in the reconstruction of Z bosons decaying into pairs of muons (Z to mu mu gamma). The present ATLAS reconstruction of photons well-separated from Z-boson muons is extended by exploiting the longitudinal segmentation of the ATLAS liquid argon calorimeter to reconstruct photons collinear with the muons emitted in the Z decay. An algorithm for the reconstruction of such photons has been developed. Using data corresponding to an integrated luminosity of 164 pb^{-1} at a centre-of-mass energy sqrt{s}=7 TeV, the photon energy, transverse energy and pseudorapidity distributions are compared to expectation from Monte Carlo simulation and good agreement is found.