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

Abstract

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 2 < Q2 < 80 GeV2, 30 < W < 210 GeV and |t| < 1 GeV2, 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 2 < Q2 < 5 GeV2 were taken in the HERAI running period and correspond to an integrated luminosity of 114 pb−1. The data for 5 < Q2 < 80 GeV2 are from both HERAI and HERAII 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 σψ(2S)/σJ/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.