Timelike Compton scattering on a deuteron target

Abstract

We investigate timelike Compton scattering (TCS) on a deuteron target as a probe of the three-dimensional partonic structure of the deuteron encoded in generalized parton distributions (GPDs). Such measurements may provide new insight into the internal structure of the deuteron, and help to clarify the unresolved tensor-polarization puzzle. We present numerical estimates of the leading-order (in the strong coupling $α_s$) TCS cross section in the kinematic region relevant to future measurements at Jefferson Lab. The deuteron GPDs are evaluated within a convolution model, while the Bethe-Heitler contribution is calculated using a phenomenological parametrization of the deuteron electromagnetic form factors. In addition, we derive the theoretical expressions for the next-to-leading-order corrections to deuteron TCS, with particular emphasis on contributions from the gluon transversity GPDs. We show that these contributions can be isolated through their characteristic angular dependence in the center-of-mass frame of the produced lepton pair. Our results demonstrate the potential of deuteron TCS as a complementary probe of both the quark and gluon structure of the deuteron at Jefferson Lab.