Large momentum transfer electroproduction of mesons

The overlap representation of skewed parton distributions is discussed and applications to wide-angle Compton scattering and electroproduction of mesons are presented. The amplitudes for these processes factorise into parton-level subprocess amplitudes and form factors representing 1/x-moments of skewed parton distributions.

We apply the light-cone technique to electroproduction reaction $ep\to e\pi^+n$ long considered as a means of measuring the electromagnetic form factor of the pion. We show that the interpretation of the long-standing puzzle of large transverse cross section ($\sigma_T$) in terms of the $\gamma^*\rho\to \pi$ transition on the $\rho$ mesons in the light-cone proton is possible, but requires quite a slow decrease of the $F_{\rho\pi}(\q2)$ form factor. This interpretation can be...

We estimate the leading order amplitudes for exclusive photon and meson electroproduction reactions at large Q^2 in the valence region in terms of skewed quark distributions. As experimental investigations can currently only be envisaged at moderate values of Q^2, we estimate power corrections due to the intrinsic transverse momentum of the partons in the meson wavefunction and in the nucleon. To this aim the skewed parton distribution formalism is generalized so as to includ...

In a framework for nonperturbative QCD calculation of high energy processes, the amplitudes for photo- and electroproduction of vector mesons are written as integrals of the overlap product of photon and vector meson wave functions, multiplied by the amplitude for the scattering of $q\bar{q}$ dipole pairs off the proton. For sizes of the overlap functions that are smaller than the typical ranges of the interaction of the dipoles with the proton, the amplitudes factorize in th...

An analysis of light vector meson photoproduction at small Bjorken $x \leq 0.2$ is done on the basis of the generalized parton distributions (GPDs). Our results on the cross section and spin density matrix elements (SDME) are in good agreement with experiments.

I discuss recent applications of QCD light-cone sum rules to various form factors of pseudoscalar mesons. In this approach both soft and hard contributions to the form factors are taken into account. Combining QCD calculation with the analyticity of the form factors, one enlarges the region of accessible momentum transfers.

It is reported on an analysis of electroproduction of light vector mesons at small Bjorken-x within the handbag approach. The partonic subprocesses, meson electroproduction off quarks or gluons, are calculated within the modified perturbative approach in which quark transverse momenta are retained. The soft hadronic matrix elements, generalized parton distributions, are constructed from the CTEQ6 parton distribution functions by means of double distributions. The cross sectio...

We analyze the reactions gamma+p => M+B, with M B being either K+ Lambda, K+ Sigma0, or pi+ n, within perturbative QCD, allowing for diquarks as quasi-elementary constituents of baryons. The diquark-model parameters and the quark-diquark distribution amplitudes of the baryons are taken from previous investigations of electromagnetic baryon form factors and Compton- scattering off protons. Reasonable agreement with the few existing data at large momentum transfer is achieved i...

Vector meson electroproduction is analyzed within the two-gluon (2G) model and the generalized parton distribution (GPD) approach at small $x$-Bjorken. We demonstrate that 2G and GPD models are not completely equivalent. At the same time, both models are in reasonable agreement with available experimental data on light vector meson electroproduction.

We analyze electroproduction of light vector mesons at small Bjorken-x in an approach that includes the gluonic generalized parton distributions and a partonic subprocess, gamma g --> (q q-bar) g, q q-bar --> V. The subprocess is calculated to lowest order of perturbative QCD taking into account the transverse momenta of the quark and antiquark as well as Sudakov suppressions. Our approach allows to investigate the transition amplitudes for all kind of polarized virtual photo...