Measurement of the cross-section ratio σ_ψ(2S)/σ_J/ψ(1S) in deep inelastic exclusive ep scattering at HERA

The exclusive deep inelastic electroproduction of ψ(2S) and J/ψ(1S) at an ep centre-of-mass energy of 317 GeV has been studied with the ZEUS detector at HERA in the kinematic range 22<80 GeV², 302, where Q² is the photon virtuality, W is the photon-proton centre-of-mass energy and t is the squared four-momentum transfer at the proton vertex. The data for 22<5 GeV² were taken in the HERAI running period and correspond to an integrated luminosity of 114 pb^-1. The data for 52<80 GeV² are from both HERA I and HERA II periods and correspond to an integrated luminosity of 468 pb^-1. The decay modes analysed were μ⁺μ^- and J/ψ(1S) π⁺π^- for the ψ(2S) and μ⁺μ^- for the J/ψ(1S). The cross-section ratio σ_ψ(2S)/σ_J/ψ(1S) has been measured as a function of Q², W and t. The results are compared to predictions of QCD-inspired models of exclusive vector-meson production.