Inelastic J/ψ electroproduction in e-p collisions

Following HERA experiments our interest is focused, in the present paper, on charmonium production in lepton-proton collisions. Inelastic J/ψ 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/ψ resonance is considered as the product of the hadronization of a cc̄ pair generated via boson-gluon fusion. The leading order contribution to the differential cross section, with respect to virtual photon-proton center of mass energyW and transferred four-momentum squared Q, is written as the sum of two terms related to a colour singlet and a colour octet cc̄ 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 cc̄ pair (colour singlet and colour octet), while the third parameter takes into accout possible “hotspot” 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.