Implications of CMS analysis of photon-photon interactions for photon PDFs

Abstract

As part of a recent analysis of exclusive two-photon production of W + W - pairs at the LHC, the CMS experiment used di-lepton data to obtain an "effective" photon-photon luminosity. We show how the CMS analysis on their 8 TeV data, along with some assumptions about the likelihood for events in which the proton breaks up to pass the selection criteria, can be used to significantly constrain the photon parton distribution functions, such as those from the CTEQ, MRST, and NNPDF collaborations. We compare the data with predictions using these photon distributions, as well as the new LUXqed photon distribution. We study the impact of including these data on the NNPDF2.3QED, NNPDF3.0QED and CT14QEDinc fits. We find that these data place a useful and complementary cross-check on the photon distribution, which is consistent with the LUXqed prediction while suggesting that the NNPDF photon error band should be significantly reduced. Additionally, we propose a simple model for describing the two-photon production of W + W - at the LHC. Using this model, we constrain the number of inelastic photons that remain after the experimental cuts are applied.