QCD mechanisms for accessing the nucleon GPDs with the exclusive pion-induced Drell-Yan process at J-PARC

TL;DR

This paper discusses the theoretical description and experimental feasibility of accessing nucleon GPDs through the exclusive pion-induced Drell-Yan process at J-PARC, highlighting new QCD insights and potential measurements.

Contribution

It presents recent theoretical advances in describing the process and assesses the feasibility of measuring nucleon GPDs via pion-induced Drell-Yan at J-PARC, including soft mechanism considerations.

Findings

Feasibility study for measuring the process at J-PARC

Theoretical description of the process in terms of GPDs and pion DAs

Estimate of soft mechanisms affecting the process

Abstract

Generalized parton distributions (GPDs) encoding multidimensional information of hadron partonic structure appear as the building blocks in a factorized description of hard exclusive reactions. The nucleon GPDs have been accessed by deeply virtual Compton scattering and deeply virtual meson production with lepton beam. A complementary probe with hadron beam is the exclusive pion-induced Drell-Yan process. We discuss recent theoretical advances on describing this process in terms of the partonic subprocess convoluted with the nucleon GPDs and the pion distribution amplitudes. Furthermore, we mention the feasibility study for measuring the exclusive pion-induced Drell-Yan process, $\pi^- p \to \mu^+ \mu^- n$, via a spectrometer at the High Momentum Beamline being constructed at J-PARC in Japan. We also point out the possible soft partonic mechanisms beyond the QCD factorization framework, which could give important contributions at J-PARC kinematics, and present an estimate of the soft mechanisms making use of dispersion relations and quark-hadron duality. Realization of the measurement of the exclusive pion-induced Drell-Yan process at J-PARC will provide a new test of QCD descriptions of a novel class of hard exclusive reactions. It will also offer the possibility of experimentally accessing nucleon GPDs at large timelike virtuality.