Photons in the proton: implications for the LHC

TL;DR

This paper develops photon-inclusive parton distribution functions using the NNPDF4.0 set with QED corrections, assessing their impact on LHC processes, especially vector boson pair production at high energies.

Contribution

It introduces a new photon PDF set based on NNPDF4.0 with advanced QED evolution, improving the modeling of photon-initiated processes at the LHC.

Findings

Photon-initiated processes can contribute up to 5% in vector boson pair production.

The new PDFs show significant differences from previous sets, especially at high invariant masses.

QED effects are crucial for precise predictions of LHC processes.

Abstract

We construct a set of parton distribution functions (PDFs), based on the recent NNPDF4.0 PDF set, that also include a photon PDF. The photon PDF is constructed using the LuxQED formalism, while QED evolution accounting for O(alpha), O(alpha alphas) and O(alpha^2) corrections is implemented and benchmarked by means of the EKO code. We investigate the impact of QED effects on NNPDF4.0, and compare our results both to our previous NNPDF3.1QED PDF set and to other recent PDF sets that include the photon. We assess the impact of photon-initiated processes and electroweak corrections on a variety of representative LHC processes, and find that they can reach the 5% level in vector boson pair production at large invariant mass.