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

University of Warsaw, Faculty of Physics, L. Pasteura 5, 02-093 Warsaw, Poland

^* e-mail: cib@fuw.edu.pl

Published online: 29 November 2016

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 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.