Measurement of the cross-section ratio $\sigma \psi (2S)/\sigma J/\psi$ in deep inelastic exclusive ep scattering at HERA

Abstract

The exclusive deep inelastic electroproduction of ψ(2S) and J/ψ(1S) 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(1S)π + π − for the ψ(2S) and µ + µ − for the J/ψ(1S), and the cross-section ratio σ ψ(2S) /σ J/ψ(1S) has been measured as a function of Q 2 , W and t. The results are compared to predictions of QCD-inspired models of vector-meson production.

WG2 Highlights: Small-x, Diffraction and Vector Mesons

“…M. Wing and N. Kovalchuk presented the ZEUS measurement of the ratio of cross sections for the exclusive production of ψ and J/ψ mesons [22]. Fig.…”