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

摘要

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 HERA in 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-momentum transfer 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-meson production.