title: How Bright is the Proton? A Precise Determination of the Photon Parton Distribution Function.
abstract: It has become apparent in recent years that it is important, notably for a range of physics studies at the Large Hadron Collider, to have accurate knowledge on the distribution of photons in the proton. We show how the photon parton distribution function (PDF) can be determined in a model-independent manner, using electron-proton (ep) scattering data, in effect viewing the ep→e+X process as an electron scattering off the photon field of the proton. To this end, we consider an imaginary, beyond the Standard Model process with a flavor changing photon-lepton vertex. We write its cross section in two ways: one in terms of proton structure functions, the other in terms of a photon distribution. Requiring their equivalence yields the photon distribution as an integral over proton structure functions. As a result of the good precision of ep data, we constrain the photon PDF at the level of 1%-2% over a wide range of momentum fractions.
authors.affiliation: Department of Physics, University of California at San Diego, La Jolla, California 92093, USA.|CERN, Theoretical Physics Department, CH-1211 Geneva 23, Switzerland.
authors.forename: Aneesh
authors.initials: A
authors.lastname: Manohar
authors.affiliation: INFN, Sezione di Milano Bicocca, 20126 Milan, Italy.
authors.forename: Paolo
authors.initials: P
authors.lastname: Nason
authors.affiliation: CERN, Theoretical Physics Department, CH-1211 Geneva 23, Switzerland.
authors.forename: Gavin P
authors.initials: GP
authors.lastname: Salam
authors.affiliation: CERN, Theoretical Physics Department, CH-1211 Geneva 23, Switzerland.|Rudolf Peierls Centre for Theoretical Physics, 1 Keble Road, University of Oxford, Oxford OX1 3NP, United Kingdom.
authors.forename: Giulia
authors.initials: G
authors.lastname: Zanderighi