Abstract
Vector meson photoproduction is an important probe of nuclear structure. Light vector mesons are most sensitive to low − x structure, as long as they are not too light for perturbative QCD calculations. The ρ ′ is of interest as an intermediate mass state (between the ρ and J / ψ ) that is easier to detect than the ϕ . Using HERA data on proton targets, we make projections for lead/gold targets in ultraperipheral collisions (UPCs) at the CERN Large Hadron Collider and the BNL Relativistic Heavy Ion Collider, and for e p and e A collisions at a future electron-ion collider (EIC). We compare the UPC projections with ALICE data, and constrain the branching ratio divided by the square of the photon- ρ ′ coupling. The data prefer large couplings and small branching ratio, probably less than 25%. The photon-meson coupling predicted by generalized vector meson dominance does not fit the data. The HERA e p and ALICE UPC e Pb data exhibit very similar 4 π mass spectra, indicating that, if the system is composed of two resonances, the products of their photon couplings with their four-pion branching ratios are similar. The predicted rates are high for both UPCs and the EIC. The ρ ′ → π + π − π + π − decay can be observed at the EIC with high efficiency. In e p collisions at the highest energy, the forward B0 detector is needed to observe this channel down to the lowest achievable Bjorken − x values.