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 ( 2 S ) and J / ψ ( 1 S ) at an ep centre-of-mass energy of 317 GeV has been studied with the ZEUS detector at HERAin the kinematic range 2 Q 2 80 GeV 2 , 30 W 210 GeV and | t | 1 GeV 2 , where Q 2 is the photon virtuality, W is the photon–proton centre-of-mass energy and t is the squared four-momentumtransfer at the proton vertex. The data for 2 Q 2 5 GeV 2 were taken in the HERA I running period and correspond to an integrated luminosity of 114 pb −1 . The data for 5 Q 2 80 GeV 2 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 ( 1 S ) π + π − for the ψ ( 2 S ) and μ + μ − for the J / ψ ( 1 S ) . The cross-section ratio σ ψ ( 2 S ) / σ J / ψ ( 1 S ) has been measured as a function of Q 2 , W and t . The results are compared to predictions of QCD-inspired models of exclusive vector-mesonproduction.