Gluon GTMDs in the exclusive electroproduction of heavy-quark pairs

Abstract

We study exclusive electroproduction of heavy quark-antiquark pairs off nucleons in the framework of generalized transverse momentum dependent parton distributions (GTMDs) for gluons. The short-distance part of the process is treated at leading order in perturbative Quantum Chromodynamics and in first order in a collinear expansion, which allows identification with the description in terms of Generalized Parton Distributions (GPDs). For the results for the structure functions in terms of GTMDs and GPDs we consider only unpolarized (spin-averaged) nucleons, but include all possible azimuthal modulations that can arise. The presented results extend known expressions in the literature and are relevant for experimental studies of this exclusive process at the future Electron Ion Collider. Furthermore, we introduce a convenient decomposition of the gluon-gluon correlation matrix in terms of GTMDs, expanded in a Lorentz basis of symmetric traceless tensors obtained from the partonic momentum $k_T$ and the momentum transfer $Δ_T$. The adopted notation for the GTMDs relates to the nucleon helicity states at the amplitude level, rather than to polarization states of the incoming nucleon or of the gluons, which makes it more transparent which contributions from helicity difference and helicity flip matrix elements can be accessed with unpolarized nucleon beams.