Inelastic J/psi electroproduction in e-p collisions

Abstract

Following HERA experiments our interest is focused, in the present paper, on charmonium production in lepton-proton collisions. Inelastic J/\psi electroproduction is quite difficult to be measured due to the low rates of events; almost all experimental studies are indeed performed in photoproduction regime. J/\psi resonance is considered as the product of the hadronization of a c \bar{c} pair generated via boson-gluon fusion. The leading order contribution to the differential cross section, with respect to virtual photon-proton center of mass energy W and transferred four-momentum squared Q^2, is written as the sum of two terms related to a colour singlet and a colour octet c \bar{c} pair production respectively. This expression contains two-gluons contributions and depends on three parameters; two of them are related to the hadronization fractions in charmonium states for the c \bar{c} pair (colour singlet and colour octet), while the third parameter takes into accout possible ``hot-spot'' effects. The values of these parameters are estimated by mean of a fit to the experimental data collected by H1 collaboration at HERA. By using different gluon densities, different sets of parameters are obtained, always with good fits.