Electro- and photoproduction of muon pairs with $\mu$CLAS12: Double Deeply Virtual Compton Scattering, Timelike Compton Scattering, and $J/\psi$ production

TL;DR

This paper discusses a program using the CLAS12 detector to explore the quark and gluon structure of nucleons through di-muon production, enabling detailed GPD measurements and studies of $J/\psi$ production.

Contribution

It introduces a new experimental approach to measure beam-spin asymmetries in DDVCS and perform high-precision studies of $J/\psi$ and TCS at CLAS12.

Findings

Access to the full three-dimensional GPD phase space.

Precision near-threshold $J/\psi$ production measurements.

High-statistics studies of Timelike Compton Scattering.

Abstract

The CEBAF Large Acceptance Spectrometer for operation at 12 GeV (CLAS12) at the Thomas Jefferson National Accelerator Facility has played a central role in advancing the understanding of nucleon and nuclear structure. As increasingly precise data become available, new physics opportunities emerge that extend beyond the current capabilities of CLAS12. In this article, a program to explore the quark and gluon structure of the nucleon through di-muon electro- and photoproduction is presented. Its primary focus is the measurement of beam-spin asymmetries in Double Deeply Virtual Compton Scattering, $ep \rightarrow e^\prime \mu^+ \mu^-p^\prime $. By independently varying the incoming and outgoing photon virtualities and momentum transfer, the DDVCS measurement provides access to the Generalized Parton Distributions over their full three-dimensional phase space, extending beyond the kinematic constraints of Deeply Virtual Compton Scattering and Timelike Compton Scattering. In addition, the large acceptance and high luminosity of the $\mu$CLAS12 experiment will enable precision measurements of near-threshold $J/\psi$ production and high-statistics studies of Timelike Compton Scattering.