Measurement of the cross-section ratio sigma_{psi(2S)}/sigma_{J/psi(1S)} in deep inelastic exclusive ep scattering at HERA

TL;DR

This paper measures the ratio of production cross sections of psi(2S) to J/psi(1S) in deep inelastic electron-proton scattering at HERA, providing insights into quantum chromodynamics models of vector meson production.

Contribution

It presents the first detailed measurement of the cross-section ratio sigma_{psi(2S)}/sigma_{J/psi(1S)} as a function of Q^2, W, and t in exclusive deep inelastic scattering at HERA.

Findings

The ratio varies with Q^2, W, and t, consistent with QCD model predictions.

Data covers a broad kinematic range, improving understanding of vector meson production.

Results support existing QCD-inspired models of exclusive vector-meson electroproduction.

Abstract

The exclusive deep inelastic electroproduction of $\psi(2S)$ and $J/\psi(1S)$ at an $ep$ centre-of-mass energy of 317 GeV has been studied with the ZEUS detector at HERA in the kinematic range $2 < Q^2 < 80$ 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 $\mu^+\mu^-$ and $J/\psi(1S) \,\pi^+\pi^-$ for the $\psi(2S)$ and $\mu^+\mu^-$ for the $J/\psi(1S)$. The cross-section ratio $\sigma_{\psi(2S)}/\sigma_{J/\psi(1S)}$ 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.