On timelike Compton scattering at medium and high energies

TL;DR

This paper discusses the theoretical aspects of timelike Compton scattering (TCS), highlighting its relation to deeply virtual Compton scattering (DVCS) and the potential for high-energy TCS data from LHC ultraperipheral collisions to explore quark and gluon GPDs at small skewness.

Contribution

It emphasizes the complementarity of TCS and DVCS, analyzes their factorization with GPDs, and discusses the prospects of high-energy TCS measurements at the LHC.

Findings

TCS and DVCS share the same GPDs as soft parts.

Next-to-leading order coefficient functions differ significantly.

High-energy TCS data can probe small skewness GPDs at the LHC.

Abstract

We emphasize the complementarity of timelike and spacelike studies of deep exclusive processes, taking as an example the case of timelike Compton Scattering (TCS) i.e. the exclusive photoproduction of a lepton pair with large invariant mass, vs deeply virtual Compton scattering (DVCS) i.e. the exclusive leptoproduction of a real photon. Both amplitudes factorize with the same generalized parton distributions (GPDs) as their soft parts and coefficient functions which differ significantly at next to leading order in alpha_s. We also stress that data on TCS at very high energy should be available soon thanks to the study of ultraperipheral collisions at the LHC, opening a window on quark and gluon GPDs at very small skewness.