1,129 research outputs found
The electro-disintegration of few body systems revisited
Recent studies of the electro-disintegration of the few body systems at JLab
have revived the field. Not only recoil momentum distributions have been
determined in a single shot. But also they confirm that the diagrammatic
approach, which I developed 25 years ago, is relevant to analyze them, provided
that the Nucleon-Nucleon scattering amplitude, determined in the same energy
range, is used. They provide us with a solid starting point to address the
issue of the propagation of exotic components of hadrons in nuclear matterComment: 6 pages,7 figure
Unitarity constraints on neutral pion electroproduction
At large virtuality , the coupling to the vector meson production
channels provides us with a natural explanation of the surprisingly large cross
section of the neutral pion electroproduction recently measured at Jefferson
Laboratory, without destroying the good agreement between the Regge pole model
and the data at the real photon point. Elastic rescattering of the
provides us with a way to explain why the node, that appears at
GeV at the real photon point, disappears as soon as differs from
zero.Comment: 7 pages; 12 figures Figures 1, 2, 10, 11, 12 updated. Axial-tensor
coupling, instead of axial-vector coupling, at the b1NN verte
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
Unitarity constraints on charged pion photoproduction at large p_perp
Around , the coupling to the channel
leads to a good accounting of the charged pion exclusive photoproduction cross
section in the energy range 3 10 GeV, where experimental data
exist. Starting from a Regge Pole approach that successfully describes vector
meson production, the singular part of the corresponding box diagrams (where
the intermediate vector meson-baryon pair propagates on-shell) is evaluated
without any further assumptions (unitarity). Such a treatment provides an
explanation of the scaling of the cross section. Elastic rescattering
of the charged pion improves the basic Regge pole model at forward and backward
angles.Comment: 5 pages; 6 figure
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
Photoproduction of charm near threshold
Charm and bottom production near threshold is sensitive to the multi-quark,
gluonic, and hidden-color correlations of hadronic and nuclear wavefunctions in
QCD since all of the target's constituents must act coherently within the small
interaction volume of the heavy quark production subprocess. Although such
multi-parton subprocess cross sections are suppressed by powers of ,
they have less phase-space suppression and can dominate the contributions of
the leading-twist single-gluon subprocesses in the threshold regime. The small
rates for open and hidden charm photoproduction at threshold call for a
dedicated facility.Comment: 5 pages 5 figures Changes: 1- Added refs 24,25; 2- Added two
sentences, top of column 2 of page 3, on the definition of x, its range and
the domain of validity of the mode
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