Electromagnetic contribution to charge symmetry violation in parton distributions

TL;DR

This paper calculates the combined electromagnetic and quark mass difference effects on charge symmetry violation in nucleon parton distributions, showing they account for about 40% of the NuTeV anomaly.

Contribution

It introduces a combined calculation of photon radiation and quark mass differences on CSV in parton distributions, incorporating coherent radiation and lattice QCD results.

Findings

CSV effect on d-u distribution difference is 20% larger at 5 GeV^2 scale.

Combined CSV sources account for approximately 40% of the NuTeV anomaly.

The study integrates QCD and QED evolution for the distributions.

Abstract

We report a calculation of the combined effect of photon radiation and quark mass differences on charge symmetry violation (CSV) in the parton distribution functions of the nucleon. Following a recent suggestion of Martin and Ryskin, the initial photon distribution is calculated in terms of coherent radiation from the proton as a whole, while the effect of the quark mass difference is based on a recent lattice QCD simulation. The distributions are then evolved to a scale at which they can be compared with experiment by including both QCD and QED radiation. Overall, at a scale of 5 GeV$^2$, the total CSV effect on the phenomenologically important difference between the $d$ and $u$-quark distributions is some 20\% larger than the value based on quark mass differences alone. In total these sources of CSV account for approximately 40\% of the NuTeV anomaly.