Exclusive Electroproduction of $\rho^0$ and $J/\psi$ Mesons at HERA

TL;DR

This paper reports measurements of exclusive $ ho^0$ and $J/ ho$ meson production in electron-proton collisions at HERA, analyzing cross sections and spin-density matrix elements to compare with theoretical models of soft and hard QCD processes.

Contribution

It provides new experimental data on cross sections and spin-density matrix elements for exclusive meson production over a range of Q^2 and W, testing QCD-based models.

Findings

Measured cross sections as functions of Q^2, W, and t.

Determined spin-density matrix elements for $ ho^0$ and $J/ ho$ production.

Discussed results in the context of soft and hard QCD phenomena.

Abstract

Exclusive production of $\rho^0$ and $J/\psi$ mesons in e^+ p collisions has been studied with the ZEUS detector in the kinematic range $0.25 < Q^2 < 50 GeV^2, 20 < W < 167 GeV$ for the $\rho^0$ data and $2 < Q^2 < 40 GeV^2, 50 < W < 150 GeV$ for the $J/\psi$ data. Cross sections for exclusive $\rho^0$ and $J/\psi$ production have been measured as a function of $Q^2, W$ and $t$. The spin-density matrix elements $r^{04}_{00}, r^1_{1-1}$ and $Re r^{5}_{10}$ have been determined for exclusive $\rho^0$ production as well as $r^{04}_{00}$ and $r^{04}_{1-1}$ for exclusive $J/\psi$ production. The results are discussed in the context of theoretical models invoking soft and hard phenomena.