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.
Highlights
The virtual Compton scattering (VCS) process is a versatile tool to unravel the proton electromagnetic structure beyond the information contained in its elastic form factors
A combination of both deeply virtual Compton scattering (DVCS) and timelike Compton scattering (TCS) observables allows for a stringent test of the applicability of the underlying quantum chromodynamics (QCD) factorization theorem at these kinematics
In this paper we presented the first-order quantum electrodynamic (QED) corrections on the lepton side contributing to the timelike Compton scattering process on a proton, γp → l−lþp
Summary
The virtual Compton scattering (VCS) process is a versatile tool to unravel the proton electromagnetic structure beyond the information contained in its elastic form factors. A combination of both DVCS and TCS observables allows for a stringent test of the applicability of the underlying QCD factorization theorem at these kinematics Such measurement of the TCS process at large timelike virtuality has been proposed by CLAS12@JLab [19], and recently first data of this experiment have been reported [20,21]. VIII, we present our numerical results, and show the effect of the radiative corrections on the cross sections as well as on the forwardbackward and photon beam helicity asymmetries We show results both in the Δð1232Þ resonance region as well as in the kinematical regime of the CLAS12@JLab TCS experiment.
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