Electroproduction of Vector Mesons

Exclusive electroproduction of vector mesons (VMs) is a particularly good process for studying the transition from the soft to the hard regime of strong interactions [1], the former being well described within the Regge phenomenology while the latter by perturbative QCD (pQCD). The interest in this interplay comes from the need to understand at which scale a partonic language is applicable. The exclusive electroproduction of VMs can then be used to extract information about the generalized parton distributions (GPDs) [2], an essential addition to understanding the partonic wave-function of the proton. Among the most striking expectations [1] in this transition is the change of the logarithmic derivative δ of the cross section σ with respect to the γp center-of-mass energyW , from a value of about 0.2 in the soft regime to 0.8 in the hard one, and the decrease of the exponential slope b of the differential cross section with respect to the squared-four-momentum transfer t, from a value of about 10 GeV to an asymptotic value of about 5 GeV when the virtuality Q of the photon increases.