We compare the single inclusive spectra of isolated photons measured at high transverse energy in proton-antiproton collisions at $\sqrt{s}=1.96\mathrm{TeV}$ with next-to-leading-order perturbative QCD predictions with various parametrizations of the parton distribution functions (PDFs). Within the experimental and theoretical uncertainties, the Tevatron data can be reproduced equally well by the recent CTEQ6.6, MSTW08, and NNPDF1.2 PDF sets. We also present the predictions for isolated $\gamma$ spectra in proton-proton collisions at $\sqrt{s}=14\mathrm{TeV}$ for central ($y=0$) and forward ($y=4$) rapidities relevant for LHC experiments. Different proton PDFs result in maximum variations of order $\pm 30\%$ in the expected $E_T^{\gamma }$-differential isolated $\gamma$ cross sections. The inclusion of the isolated photon data in global PDF fits will place extra independent constraints on the gluon density.

• Received 23 May 2010

DOI:https://doi.org/10.1103/PhysRevD.82.014015