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

We evaluate the leading-order QED radiative corrections to the timelike Compton scattering (TCS) process gamma p -> 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 dilepton 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 parametrizations for a recent CLAS12@JLab TCS experiment.

Automated summary

We studied the leading-order QED radiative corrections to the timelike Compton scattering process and found that they range from 5%-10% in the low-energy regime and around 20% in the high-energy regime. These corrections nearly cancel out in both dilepton forward-backward asymmetry and photon beam helicity asymmetry, making them ideal observables for extracting the real and imaginary parts of the TCS amplitude. Our results demonstrate the sensitivity of these asymmetries to GPD parametrizations in recent TCS experiments at CLAS12@JLab.