Exclusive production of a pair of high transverse momentum photons in pion-nucleon collisions for extracting generalized parton distributions

TL;DR

This paper proposes a QCD-based method to study exclusive high transverse momentum photon pair production in pion-nucleon collisions, enabling extraction of generalized parton distributions with enhanced sensitivity.

Contribution

It introduces a systematic factorization approach for this process, demonstrating process-independence of non-perturbative contributions and potential for improved GPD extraction.

Findings

Process-independent factorization into DAs and GPDs

Enhanced sensitivity to parton momentum fraction x

Quantitative demonstration of the method's effectiveness

Abstract

We show that exclusive production of a pair of high transverse momentum photons in pion-nucleon collisions can be systematically studied in QCD factorization approach if the photon's transverse momentum $q_T$ with respect to the colliding pion is much greater than $\Lambda_{\rm QCD}$. We demonstrate that the leading power non-perturbative contributions to the scattering amplitudes of this exclusive process are process-independent and can be systematically factorized into universal pion's distribution amplitudes (DAs) and nucleon's generalized parton distributions (GPDs), which are convoluted with corresponding infrared safe and perturbatively calculable short-distance hard parts. The correction to this factorized expression is suppressed by powers of $1/q_T$. We demonstrate quantitatively that this new type of exclusive processes is not only complementary to existing processes for extracting GPDs, but also capable of providing an enhanced sensitivity to the dependence of both DAs and GPDs on the active parton's momentum fraction $x$. We also introduce additional, but the same type of exclusive observables to enhance our capability to explore GPDs, in particular, their $x$-dependence.