Leading-order QED radiative corrections to timelike Compton scattering on the proton

TL;DR

This paper calculates leading-order QED radiative corrections to timelike Compton scattering on the proton across different energy regimes, showing their impact on cross sections and asymmetries, and highlighting their importance for GPD extraction.

Contribution

It provides the first detailed analysis of QED radiative corrections to TCS in both low- and high-energy regimes using different models, including GPD-based approaches.

Findings

Radiative corrections are 5-10% at low energy and around 20% at high energy.

Certain asymmetries nearly cancel radiative corrections, making them ideal for GPD studies.

Sensitivity of asymmetries to GPD parameterizations demonstrated for CLAS12@JLab.

Abstract

We evaluate the leading-order QED radiative corrections to the timelike Compton scattering (TCS) process $\gamma p \to l^- l^+ p$. We study these corrections in two energy regimes using different models for the TCS amplitude. In the low-energy regime we calculate the contribution due to the proton and its lowest-energy excitation, the $\Delta(1232)$ resonance. In the high-energy near-forward kinematical regime we calculate the TCS amplitude in a handbag approach in terms of Generalized Parton Distributions (GPDs). On the level of cross sections we find the QED radiative corrections to be in the $5 -10\%$ range in the low-energy regime and around $20\%$ in the high-energy regime. We show that in both the di-lepton forward-backward asymmetry as well as in the photon beam helicity asymmetry these corrections nearly cancel out, making them gold-plated observables to extract the real and imaginary parts of the TCS amplitude. We demonstrate in particular the sensitivity of these asymmetries on GPD parameterizations for a recent CLAS12@JLab TCS experiment.