Implication of CMS data on photon PDFs

TL;DR

This paper analyzes CMS data on two-photon production of W+ W- pairs at the LHC to constrain photon parton distribution functions, showing that experimental data can significantly improve photon PDF accuracy and consistency with theoretical models.

Contribution

It demonstrates how CMS di-lepton data constrains photon PDFs and compares different photon distribution models, proposing a simple model for two-photon W+ W- production at the LHC.

Findings

CMS data constrains photon PDFs effectively.

Photon distributions are consistent with LUXqed predictions.

Data suggests NNPDF photon error bands can be reduced.

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 usefil and complementary cross-check on the photon distribution, which is consistent with 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 amount of inelastic photon that remains after the experimental cuts are applied.