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

Abstract

The exclusive deep inelastic electroproduction of $\ddot{I}ˆ(2S)$ and $J/\ddot{I}ˆ(1S)$ 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 $\hat{I}{¼}^{+}\hat{I}{¼}^{-}$ and $J/\ddot{I}ˆ(1S)\ddot{I}{€}^{+}\ddot{I}{€}^{-}$ for the $\ddot{I}ˆ(2S)$ and $\hat{I}{¼}^{+}\hat{I}{¼}^{-}$ for the $J/\ddot{I}ˆ(1S)$. The cross-section ratio $\ddot{I}{ƒ}_{\ddot{I}ˆ(2S)}/\ddot{I}{ƒ}_{J/\ddot{I}ˆ(1S)}$ 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.

24 pages, 8 figures