Large momentum transfer electroproduction of mesons

The soft physics approach to form factors and Compton scattering at moderately large momentum transfer is reviewed. It will be argued that in that approach the Compton cross section is given by the Klein-Nishina cross section multiplied by a factor describing the structure of the proton in terms of two new form factors. These form factors as well as the ordinary electromagnetic form factors represent moments of skewed parton distributions.

A review of recent precision measurements of the electromagnetic form factors of the mesons, pion and kaon, and the hyperons, $\Lambda^0$, $\Sigma^0$, $\Sigma^+$, $\Xi^-$, $\Xi^0$, $\Omega^-$, at large timelike momentum transfers is presented. Evidence is found for diquark correlations in $\Lambda^0$, $\Sigma^0$ hyperons.

In this thesis we discuss a rational and data-based description of the single- and double-virutal transition form factors of the lightest pseudoscalar mesons. We obtain an accurate description of these in the spacelike and low-energy timelike regions. The phenomenological applications are wide. Among them, we discuss, the eta-eta' mixing, the rare pseudoscalar decays into a lepton pair and the pseudoscalar-pole contribution to the hadronic light-by-light part of the anomalous...

I describe recent advances in our understanding of the hadronic form factors governing semileptonic meson transitions. The resulting framework provides a systematic approach to the experimental data, as a means of extracting precision observables, testing nonperturbative field-theory methods, and probing a poorly understood limit of QCD.

Form factors of the proton, pion, and kaon for large timelike momentum transfers have recently been measured with precision. The results and future prospects are discussed.

We examine the use of phenomenological form factors in tree level amplitudes for meson photoproduction. Two common recipes are shown to be fundamentally incorrect. An alternate form consistent with gauge invariance and crossing symmetry is proposed.

It is reported on an analysis of electroproduction of light 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 by means of double distributions. The constraints from parton distributions and sum rules are taken in...

A new mechanism of baryon-antibaryon production via nonperturbative double pair creation in intermediate mesons is proposed and the theory contains no fitting parameters. It is shown, that near-threshold resonances are responsible for enhancements in electroproduction cross sections: $\psi(4S)$ for $\Lambda^+_c \Lambda^-_c, \Upsilon (6S)$ for $\Lambda_b \bar \Lambda_b$. An admixture of intermediate $D$- wave resonances produces angular dependence in differential cross section...

The amplitude ratios of vector-meson production by heavy photons on spinless targets are shown to can be explicitly expressed in terms of the spin-density-matrix elements (SDMEs) only if the lepton beam is longitudinally polarized. Making use of the amplitude ratios as free fit parameters instead of the SDMEs reduces the number of the real parameters in data description from 23 to 8. The exact formula for $R = \frac{d \sigma_L}{d t}/\frac{d \sigma_T}{d t}$ in terms of the SDM...

A general description of proton form factors is presented, in the whole kinematical region. The existing data and selected phenomenological models are briefly discussed.