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

Abstract

Ultra-peripheral 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 γp → 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 LHC, the final states are produced at far forward rapidities. For lower energy colliders, the systems are produced closer to mid-rapidity, within reach of central detectors. * srklein@lbl.gov † xieyp@lbl.gov

Near-threshold photoproduction of $$J/\psi $$ in two-gluon exchange model

“…The exclusive electroproduction of J/ψ is closely connected J/ψ photoproduction, as in the electron scattering process the J/ψ vector meson is generated from the virtual photon exchanged between the electron and the hadron. The electroproduction cross-section of J/ψ in electron-proton scattering can be found in the recent literatures [42,43], σ (ep → e J/ψ p)…”

Near threshold heavy vector meson photoproduction at LHC and EicC

“…In order to describe the exclusive vector meson photoproduction in electron-hadron and ultraperipheral hadronic collisions, we will assume the validity of the Equivalent Photon Approximation (EPA) [65], which allow us to factorize the cross sections in terms of the photon fluxes, associated to the electron and to the hadron, and the photon-hadron cross section. In particular, for the exclusive production of a vector meson V in eh collisions, with h = p or A, the cross section can be written as [66,67]…”

“…As in Refs. [66,67], we will assume that the Q 2 dependence of the γ h cross section can be factorized as follows…”

Photonuclear and Two-Photon Interactions at High-Energy Nuclear Colliders

“…Reggeon exchange rates are high. The predicted photoproduction rate for the a + 2 (1320), a "standard candle" qq meson, is about a billion mesons per year at both RHIC and the LHC (105). Thus, states with small couplings to photons can be observed.…”