Exclusive production of quarkonia as a probe of the GPD E for gluons
  Exclusive quarkonium photo- and electro-production off the nucleon is studied in the framework of generalized parton distributions (GPDs). The short distance part of the process is treated at leading order in perturbative Quantum Chromodynamics. The main focus is on the GPD E for gluons. On the basis of different models for E we estimate the transverse target spin asymmetry for typical kinematics of a future Electron Ion Collider. We also explore the potential of measuring the polarization of the recoil nucleon. 
John Koempel, Peter Kroll, Andreas Metz, Jian Zhou
hep-ph hep-ex