Photoproduction of charged final states in ultraperipheral collisions and electroproduction at an electron-ion collider

Ultraperipheral collisions (UPCs) of relativistic ions are an important tool for studying photoproduction at high energies. Vector-meson photoproduction is an important tool for nuclear structure measurements and other applications. A future electron-ion collider (EIC) will allow additional studies, using virtual photons with a wide range of Q(2). We propose a significant expansion of the UPC and EIC photoproduction physics programs to include charged final states which may be produced via Reggeon exchange. We consider two examples: a(2)(+) (1320), which is a conventional qq meson, and the exotic Z(c)(+) (4430) state (modeled here as a tetraquark). The Z(c)(+) (4430) cross section depends on its internal structure, so photoproduction can test whether the Z(c)(+) (4430) is a tetraquark or other exotic object. We calculate the rates and kinematic distributions for gamma p -> X+ n in pA UPCs and ep collisions at an EIC and in UPCs. The rates are large enough for detailed studies of these final states. Because the cross section for Reggeon exchange is largest near threshold, the final-state rapidity distribution depends on the beam energies. At high-energy colliders like the proposed LHeC or pA collisions at the Large Hadron Collider, the final states are produced at far forward rapidities. For lower energy colliders, the systems are produced closer to midrapidity, within reach of central detectors.