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

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.

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

Calculations of the Exclusive Processes 2H(e,e'p)n, 3He(e,e'p)2H and 3He(e,e'p)(pn) within a Generalized Glauber Approach

The exclusive processes 2H(e,e'p)n, 3He(e,e'p)2H and 3He(e,e'p)(pn), have been analyzed using realistic few-body wave functions and treating the final state interaction (FSI) within a Generalized Eikonal Approximation (GEA), based upon the direct calculation of the Feynman diagrams describing the rescattering of the struck nucleon with the nucleons of the A-1 system. The approach represents an improvement of the conventional Glauber approach (GA), in that it allows one to take into account the effects of the nuclear excitation of the $A-1$ system on the rescattering of the struck nucleon. Using realistic three-body wave functions corresponding to the AV18 interaction, the results of our parameter free calculations are compared with available experimental data. It is found that in some kinematical conditions FSI effects represent small corrections, whereas in other kinematics conditions they are very large and absolutely necessary to provide a satisfactory agreement between theoretical calculations and experimental data. It is shown that in the kinematics of the experimental data which have been considered, covering the region of missing momentum and energy with p_m < 0.6 GeV/c and E_m < 100 MeV in the perpendicular kinematics, the GA and GEA predictions differ only by less than 3-4 %.Comment: Typos detected and removed while Proof reading. Physical Review C. in Pres