Inelastic leptoproduction of $J/\psi$ mesons at HERA

Abstract.

The leptoproduction of $J/\psi$ mesons is studied in inelastic reactions for four momentum transfers $2 < Q^2 < 100 GeV^2$. The data were taken with the H1 detector at the electron proton collider HERA and correspond to an integrated luminosity of $77 pb^{-1}$. Single differential and double differential cross sections are measured with increased precision compared with previous analyses. New leading order calculations within the non-relativistic QCD factorisation approach including colour octet and colour singlet contributions are compared with the data and are found to give a reasonable description of most distributions. An exception is the shape of the distribution in the $J/\psi$ fractional energy, z, which deviates significantly from that of the data. Comparisons with photoproduction are made and the polarisation of the produced $J/\psi$ meson is analysed.