Diffractive Vector Meson figures
Diffractive vector meson production, e+A→e’+A’+V where V=J/ψ, φ, ρ, or γ, is a unique process, because it allows the measurement of the momentum transfer, t, at the hadronic vertex even in e+A collisions where the 4-momentum of the outgoing nuclei cannot be measured. Since only one new final state particle is created,the process is experimentally clean and can be unambiguously identified by the presence of a rapidity gap. J/ψ with its compact dipole size is not particularly sensitive to the gluon saturation. Larger mesons such as φ or ρ are considerably more sensitive to saturation effects. We have carried out the simulation of these vector meson productions in the diffractive processes. Instead of deriving |t| from the 4-momentum of the scattered electron and the created vector mesons, an approximation using the transverse momenta of these two particles |t|=(pxe’+pxV)2+(pye’+pyV)2 is found to achieve good absolute value and resolution. The achieved resolution of st/t~=2.5% is shown to be able to allow eSTAR measurement to clearly follow the input diffractive pattern required in EIC whitepaper.