Speaker
Description
Progress is reported with a new phenomenological analysis in full view of chromodynamics of measurements of exclusive elastic (ep->eVMp) and dissociative electroproduction (ep->eVMN) cross sections for the production of vector-meson (VM) “quarkonia” of different flavour, namely
rho(760), phi(1019), J/Psi and Y(9460). First results are presented of an acceptable fit to all measurements of virtual photoproduction cross sections sigma_(gammap->VMp) made by the H1 and Zeus experiments at HERA. The approach is based on the factorisable combination of flavor-dependent, Bethe-Heitler, photon-splitting gamma->qqbar/qqbar and of flavour-blind, elastic, quark-proton (qp-> qpq) scattering with appreciation that in an initially collinear qp configuration the presence of a space-like quark q defines a scale which amounts to the “length” of the qp->qp interaction. The photon-splitting is taken from the consistency of measurements of the real and virtual photon structure function in inelastic electron-positron scattering (ee->ee+hadrons) with leading order Bethe-Heitler splitting. For flavour-blind elastic (qq->qp) scattering, a Regge-asymptotic form with only a single pole with a trajectory whose intercept is Q2-dependent and which is within a range consistent with what tradition demands, namely the “pomeron”, is taken from the analysis in terms of forward elastic u/dp->u/d*p scattering by H1 of their measurements of the inclusive electroproduction of hadrons. The measurements are all well described by this approach taking “constituent masses” for the u, d, c, and b quarks. The “pomeron” is thus seen both to be at work at a scale which is below that of the interacting proton, that is, of confinement, and to be universal, provided that account is taken of the collinear “length” of the quark-proton interaction. The possibility, which the success of this approach suggests, that constituent quarks are the appropriate degrees of freedom with which to formulate new understanding of hadronic matter when probed at distance scales below confinement at a future electron-ion collider, is raised.