Abstract

Exclusive electroproduction of mesons in  collisions, $\sqrt{s} \sim 310\,$, at ~310 GeV center-of-mass energy has been studied with the ZEUS detector using an integrated luminosity of 90/pb. The $ep$ state is identified via its dilepton decay channels. The exclusive $\sigma^{\gamma^*p \rightarrow J\hspace{-0.05cm}/\hspace{-0.05cm}\psi \,p}_{tot}$ total cross section has been measured as functions of $W$ and W. The helicity state of $ep$ mesons has also been measured from the angular distribution of the decay leptons, and the ratio of R is extracted as a function of $W$. These results are compared with the theoretical predictions from the Regge phenomenology and from the perturbative QCD. Back