The photon parton distribution function: updates and applications

TL;DR

This paper reviews recent advances in determining the photon parton distribution function of the proton, highlighting improved precision and methodology for applications in high-energy physics experiments like the LHC.

Contribution

It updates the photon PDF determination method using structure functions, achieving errors below 2% in a key x-range, and discusses progress since previous work.

Findings

Photon PDF errors reduced to below 2% for certain x-range.

Explicit formula for photon PDF systematically improvable in perturbation theory.

Method based on electron-proton scattering data enhances precision in proton structure modeling.

Abstract

The photon parton distribution function (PDF) of the proton is crucial for precise comparisons of LHC cross sections with theoretical predictions. However, it was previously affected by very large uncertainties of around ${\cal O}(100\%)$ or dependent upon phenomenologically inspired models. In the paper~\cite{Manohar:2016nzj}, we demonstrated how the photon PDF could be determined using the proton structure functions $F_2$ and $F_L$ measured in electron--proton scattering experiments. We provided an explicit formula for the PDF, which can be systematically improved order by order in perturbation theory. We obtained a photon PDF with errors $\lesssim 2$\% for $10^{-4} < x < 0.1$. Here, we recall the underlying idea and method used to obtain this result, as well as the progress made since then.