552 research outputs found
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, and
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 mass spectrum. On the contrary, a cusp would be easily
detected near the production threshold in the 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
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
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
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