Data-driven study of timelike Compton scattering

Abstract

In the framework of collinear QCD factorization, the leading twist scattering amplitudes for deeply virtual Compton scattering (DVCS) and timelike Compton scattering (TCS) are intimately related thanks to analytic properties of leading and next-to-leading order amplitudes. We exploit this welcome feature to make datadriven predictions for TCS observables to be measured in near future experiments. Using a recent extraction of DVCS Compton form factors from most of the existing experimental data for that process, we derive TCS amplitudes and calculate TCS observables only assuming leading-twist dominance. Artificial neural network techniques are used for an essential reduction of model dependency, while a careful propagation of experimental uncertainties is achieved with replica methods. Our analysis allows for stringent tests of the leading twist dominance of DVCS and TCS amplitudes. Moreover, this study helps to understand quantitatively the complementarity of DVCS and TCS measurements to test the universality of generalized parton distributions, which is crucial e.g. to perform the nucleon tomography.

Parton distributions and lattice-QCD calculations: Toward 3D structure

“…Work within the PARTONS framework has been also recently extended to estimate time-like Compton scattering (TCS) observables taking advantage of the complementarity between he Leading Order (LO) and Next to Leading Order (NLO) descriptions (Grocholski et al, 2020); for a model free extraction of the subtraction constant entering the dispersion relations approach to GPDs (Diehl and Ivanov, 2007) and its impact on the energy momentum tensor matrix elements (Polyakov, 2003). It is also currently used to model light nuclei GPDs, and to develop a DVCS event generator for the future EIC.…”

Phenomenological assessment of proton mechanical properties from deeply virtual Compton scattering

“…References [36][37][38][39] provide a recent account of the experimental and phenomenological status and prospects of three exclusive channels which attract most of current experimental interest, namely DVCS, deeply virtual meson production (DVMP) and timelike Compton scattering (TCS).…”

Exclusive production of a large mass photon pair

“…Finally, let us stress that NLO QCD corrections are likely to be important and should definitely be computed before a sensible phenomenology of our process is undertaken. Together with a further hint of the factorization of our process, it should yield an intersting information on the analytic structure of these QCD corrections in a process where both timelike M 2 γγ and spacelike Q 2 scales coexist, in contradistinction with the DVCS vs TCS cases [18,19].…”