Related papers: Fermi Motion and Quark Off-Shellness in Elastic Ve…
We show that the ratio of the transverse to the longitudinal cross sections observed at HERA cannot be reproduced by models which assume that the meson can be described by an on-shell q qbar pair. We explain how a simple model allowing…
We reexamine the Fermi motion effects on the diffractive photo- and electroproductions of heavy vector-mesons, J/psi and psi', off a nucleon in the leading ln(Q^2/Lambda_QCD^2) approximation (LLA) of QCD. We take into account all the Fermi…
Hard diffractive electroproduction of longitudinally polarized vector mesons is calculated within the leading $\alpha_s\ln{Q^2\over\Lambda_{QCD}^2}$ approximation of QCD using the leading order parton densities within the nucleon. Novel QCD…
We show that the lowest-order QCD calculation in a simple model of elastic vector-meson production does reproduce correctly the ratios of cross sections for rho, phi and J/psi, both in photoproduction and in high-Q2 quasi-elastic…
A compilation of H1 and ZEUS cross section measurements for elastic vector meson production is presented as a function of the scale $K^2 = (Q^2+M_V^2)/4$, where Q^2 is the exchanged photon virtuality and M_V is the mass of the vector meson.…
A nonperturbative calculation of elastic electroproduction of the J/psi meson is presented and compared to the experimental data. Our model describes well the observed dependences of the cross sections on the photon virtuality Q2 and on the…
Exclusive diffractive processes on the nucleon are investigated within a model in which the quark-nucleon interaction is mediated by Pomeron exchange and the quark substructure of mesons is described within a framework based on the…
Hard diffractive photo- and electroproduction of heavy vector mesons ($J/\psi$ and $\Upsilon$) is evaluated within the leading $\alpha_s\ln{Q^2 \over\Lambda_{QCD}^2}$ approximation of QCD. In difference from our earlier work on that…
We discuss recent HERA results on vector--meson electroproduction gamma*p -> Vp and demonstrate that universality of the initial and final state interactions responsible for the transition between the on- and off-mass shell states allows to…
The differential cross section $d\sigma/dq^2$ of diffractive electroproduction of heavy quarkonia on protons is a sensitive study tool for the interaction dynamics within the dipole representation. Knowledge of the transverse momentum…
In a previous analysis of electroproduction of hypernuclei the cross sections were calculated in distorted-wave impulse approximation where the momentum of the initial proton in the nucleus was set to zero (the frozen-proton approximation).…
The H1 and ZEUS Collaborations report new results on elastic VM cross-section and trajectory determination. Elastic VM production appears to be independent of the photon polarization. The presence of non-zero shrinkage in the…
Differential cross sections of the photo- and electroproduction of the hypertriton have been calculated by utilizing modern nuclear wave functions and the elementary operator of KAON-MAID. It is found that a proper treatment of Fermi motion…
It is shown that the universality of the initial and final state interactions responsible for the transition between the on-- and off--mass shell states leads to the energy independence of the ratio of exclusive $\rho$ electroproduction…
We consider backward vector meson exclusive electroproduction off nucleons in the framework of collinear QCD factorization. Nucleon to vector meson transition distribution amplitudes arise as building blocks for the corresponding factorized…
We investigate $\phi$-meson electroproduction off the proton target, i.e., $\gamma^* p \to \phi p$, by employing a tree-level effective Lagrangian approach in the kinematical ranges of $Q^2$ = (0$-$4) $\mathrm{GeV}^2$, $W$ = (2$-$5) GeV,…
The elastic production of vector mesons at HERA is discussed from the theoretical point of view. We briefly review different models, their successes and shortcomings. Main emphasis is put on recent issues in perturbative QCD calculations.…
Deep-inelastic scattering at low x and elastic vector meson production are considered on the basis of the off-shell extension of the s-channel unitarity. We discuss behavior of the structure function F_2(x,Q^2) at low x and the total…
The elastic electroproduction of phi mesons is studied at HERA with the H1 detector for photon virtualities 1 < Q^2 < 15 GeV^2 and hadronic centre of mass energies 40 < W < 130 GeV. The Q^2 and t dependences of the cross section are…
We show that the lowest-order QCD calculation in a simple model of elastic vector-meson production does reproduce correctly the ratios of cross sections for rho, phi and J/psi (measured by H1 and ZEUS), both in photoproduction and in…