Sensitivity of isolated photon production at TeV hadron colliders to the gluon distribution in the proton

TL;DR

This paper compares experimental isolated photon spectra at Tevatron with QCD predictions using various PDFs, showing significant sensitivity to the gluon distribution and implications for future LHC measurements.

Contribution

It demonstrates the sensitivity of isolated photon production to the gluon distribution in the proton and highlights the potential of photon data to constrain PDFs.

Findings

Tevatron data can be reproduced by multiple PDF sets within uncertainties.

Different PDFs cause up to 30% variation in predicted photon spectra.

Photon data can provide additional constraints on the gluon density in the proton.

Abstract

We compare the single inclusive spectra of isolated photons measured at high transverse energy in proton-antiproton collisions at sqrt(s)=1.96 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 present also the predictions for isolated gamma spectra in proton-proton collisions at sqrt(s)=14TeV for central (y=0) and forward (y=4) rapidities relevant for LHC experiments. Different proton PDFs result in maximum variations of order 30% in the expected E_T-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.