Rescattering in Meson Photoproduction off Few Body Systems

Exclusive reactions induced at high momentum transfer in few body systems provide us with an original way to study the production and propagation of hadrons in cold nuclear matter. In very well defined parts of the phase space, the reaction amplitude develops a logarithmic singularity. It is on solid ground since it depends only on on-shell elementary amplitudes and on low momentum components of the nuclear wave function. This is the best window to study the propagation of exotic configurations of hadrons such as, for instance, the onset of color transparency. It may appear earlier in meson photo-production reactions, more particularly in the strange sector, than in more classical quasi elastic scattering of electrons. More generally, those reactions provide us with the best tool to determine the cross section of the scattering of various hadrons (strange particles, vector mesons) from the nucleon and to access the production of possible exotic states.Comment: 15 pages; 11 figures During the review process of the paper, the following changes have been implemented: 1- The title has been changed, 2- The abstact and the first paragraph of the introduction have been rephrased for consistency; 3- Figure 10 has been added; 4- The Appedix has been considerably expanded: it gives the full expressions of the elementary photoproduction amplitudes in terms of Pauli spinors and matrice

Pentaquark, cusp and rescattering in single kaon photoproduction off deuterium

In very well defined part of the phase space, $K N$ and $\Lambda N$ rescattering depend on on-shell elementary matrix elements and on the low momentum components of the deuteron wave function. This provides us with the unique opportunity to study details in the scattering amplitudes that may have escaped the analysis of reactions induced on a nucleon target by Kaon and Hyperon beams at low energies. When folded with a typical experimental mass resolution, a narrow state with a width of 1 MeV would contribute by no more than 10% to the $KN$ mass spectrum. On the contrary, a cusp would be easily detected near the $\Sigma$ production threshold in the $\Lambda N$ mass spectrum.Comment: 7 pages; 7 figures Updated version after referees' review. Main changes: 1- The contribution of positive parity pentaquark has also been considered; 2- Figure 5 has been added. It shows the expected angular distributions of the contribution of a positive or negative parity pentaquark; 3- Units in Figure 4 and 7 have been updated; 4- The reference list has been update

Strangeness Production by Electromagnetic and Hadronic Probes

After pioneering works on hypernuclei, strangeness production mechanisms have been studied in hadron collisions and photoreactions in the sixties. Recent experiments at SATURNE and COSY, in the hadronic sector, as well as ELSA and JLab, in the electromagnetic sector, have confirmed our basic ideas on the reaction mechanisms. In the near future, strangeness production at JLab, HERMES and COMPASS may prove to be a powerful tool to study hadronic matter.Comment: 10 pages, 9 figures; Invited talk at HYP2000 Conference, Torino, Italy, 23-27 October 2000. To appear in Nucl. Phys.

The photoproduction of vector mesons

At high energy, the photoproduction or electroproduction of Vector Mesons allow to prepare a beam of quark-antiquark pairs of a given flavor. At high momentum transfer, the study of the scattering of these pairs on a nucleon opens up an original window on the quark-gluon structure of hadronic matter, which may eventually shed light on its gluonic content, on correlations between quarks and on the van der Walls part of the interaction between hadrons.Comment: 10 pages; 9 figures; Invited talk at the "Third International Conference on Perspectives in Hadronic Physics", Trieste (Italy), 7--11 May 2001; Nucl. Phys. A, in pres

The Primakoff effect on a proton target

Primakoff effect offers us with a way to determine the radiative decay width of pseudo-scalar mesons when they are photo-produced in the electromagnetic field of hadronic systems. Taking advantage of recent developments in the Regge description of the production of mesons in the strong hadronic field, this paper evaluates the relative importance of the electromagnetic and the strong amplitudes, and assesses the possibilities which become opened by modern experimental facilities.Comment: 4 pages; 5 Figure

Real and Virtual Compton Scattering in a Regge Approach

We study Real and Deeply Virtual Compton Scattering in a model based on Regge trajectories and two-gluon exchange. In the kinematic regime of current experiments, the hadronic component of the outgoing real photon plays a major role. We analyze the spin structure of Compton scattering at large momentum transfer and give predictions for several spin asymmetries. In the DVCS channel, a fairly good agreement is obtained for the recently measured beam spin and charge asymmetries.Comment: 12 pages; 6 figures This revised version corrects a mumerical mistake in the evaluation of the conversion factor between vector mesons and Compton amplitudes. Also, more details are given on the parameters of the sigma meson amplitud

Quark correlations and gluon propagators in elastic vector meson production

We study the behavior of the differential cross section for vector meson photoproduction at large momentum transfer in the two-gluon exchange model. We focus on the treatment of two-quark correlation function in the proton and on gluon propagators with a dynamically generated mass. We find that only the large t region is sensitive to the particular details of these inputs.Comment: 4 pages, 2 figures, espcrc1.sty included, Proceedings of the Third International Conference on Perspectives in Hadronic Physic

Electroproduction of strangeness above the resonance region

A simple and elegant model, based on Reggeized t-channel exchanges is succesful in reproducing the main features of all existing data of the reactions ep->eKLambda and ep->eKSigma. In particular, the original way gauge invariance is taken into account is found to be essential to describe the ratio between the Coulomb and the Transverse cross-sections at large Q2 that has been measured recently at JLab.Comment: 5 pages, 5 figures, submitted to Phys.Rev.Let

Photoproduction of Vector Mesons at Large Transfer

At forward angles, the cross-sections of photoproduction of vector mesons ($\rho$, $\omega$, and $\phi$) are well accounted for by the exchange of the Pomeron at high energies, while contributions of $t$ channel exchange of Reggeons are significant at low energies. At large angles, the impact parameter becomes small enough to prevent their constituents to build up the exchanged Reggeons or Pomeron. Two gluon exchange appears to dominate above $-t\simeq 1$ GeV$^2$, especially in the $\phi$ channel.Comment: 4 pages, 3 figure