46 research outputs found
The Kaon-Photoproduction Of Nucleons In The Quark Model
In this paper, we develop a general framework to study the
meson-photoproductions of nucleons in the chiral quark model. The S and U
channel resonance contributions are expressed in terms of the
Chew-Goldberger-Low-Nambu (CGLN) amplitudes. The kaon-photoproduction
processes, , , and , are calculated. The initial results show that the quark
model provides a much improved description of the reaction mechanism for the
kaon-photoproductions of the nucleon with less parameters than the traditional
phenomenological approaches.Comment: 25 pages, 9 postscript figures can be obtained from the author
An Unified Approach To Pseudo Scalar Meson Photoproductions Off Nucleons In The Quark Model
An unified approach to the pseudo scalar meson (, and )
photoproduction off nucleons are presented. It begins with the low energy QCD
Lagrangian, and the resonances in the s- and u- channels are treated in the
framework of the quark model
The duality hypothesis is imposed to limit the number of the t-channel
exchanges. The CGLN amplitudes for each reaction are evaluated, which include
both proton and neutron targets. The important role by the S-wave resonances in
the second resonance region is discussed, it is particularly important for the
and photoproductions.Comment: 31 pages in Latex fil
Inclusive and exclusive photoproduction on the deuteron: - and -threshold phenomena
Inclusive and exclusive photoproduction on the deuteron are
investigated theoretically. Modern hyperon-nucleon forces and a recently
updated kaon photoproduction operator for the process are
used. Sizable effects of the hyperon-nucleon final state interaction are found
near the and thresholds in the inclusive reaction.
Angular distributions for the exclusive process show clear final state
interaction effects in certain kinematic regions. Precise data especially for
the inclusive process around the threshold would help to clarify
the strength and property of the interaction.Comment: 14 pages, 10 figure
Pseudoscalar meson photoproduction: from known to undiscovered resonances
The role of dynamics in spin observables for pseudoscalar meson
photoproduction is investigated using a density matrix approach in a multipole
truncated framework. Extraction of novel rules for and reactions based on resonance dominance, and on
other broad and reasonable dynamical assumptions, are discussed. Observables
that are particularly sensitive to missing nucleonic resonances predicted by
quark-based approaches, are singled out.Comment: 22 pages, latex, 3 figure
Hyperon-Nucleon Final State Interaction in Kaon Photoproduction of the Deuteron
Final state hyperon-nucleon interaction in strangeness photoproduction of the
deuteron is investigated making use of the covariant reaction formalism and the
P-matrix approach to the YN system. Remarkably simple analytical expression for
the amplitude is obtained. Pronounced effects due to final state interaction
are predicted including the manifestation of the 2.13 GeV resonance.Comment: LaTeX, 13 page
Form factors and photoproduction amplitudes
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.Comment: To be published in PR
Production Processes as a Tool to Study Parameterizations of Quark Confinement
We introduce diquarks as separable correlations in the two-quark Green's
function to facilitate the description of baryons as relativistic three-quark
bound states. These states then emerge as solutions of Bethe-Salpeter equations
for quarks and diquarks that interact via quark exchange. When solving these
equations we consider various dressing functions for the free quark and diquark
propagators that prohibit the existence of corresponding asymptotic states and
thus effectively parameterize confinement. We study the implications of
qualitatively different dressing functions on the model predictions for the
masses of the octet baryons as well as the electromagnetic and strong form
factors of the nucleon. For different dressing functions we in particular
compare the predictions for kaon photoproduction, , and
associated strangeness production, with experimental data.
This leads to conclusions on the permissibility of different dressing
functions.Comment: 43 pages, Latex, 28 eps files included via epsfig; version to be
published in Physical Review
Exclusive Photoproduction of Large Momentum-Transfer K and K* Mesons
The reactions gamma p -> K+ Lambda and gamma p -> K* Lambda are analyzed
within perturbative QCD, allowing for diquarks as quasi-elementary constituents
of baryons. The diquark-model parameters and the quark-diquark distribution
amplitudes of proton and Lambda are taken from previous investigations of
electromagnetic baryon form factors and Compton-scattering off protons.
Unpolarized differential cross sections and polarization observables are
computed for different choices of the K and K* distribution amplitudes. The
asymptotic form of the K distribution amplitude (proportional to x1 x2) is
found to provide a satisfactory description of the K photoproduction data.Comment: 32 pages, 7 figures available as tared, compressed and uuencoded
PS-file
The pion photoproduction in the \Delta(1232) region
We investigate the pion photoproduction in the \Delta(1232) region in the
framework of an effective Lagrangian including pions, nulceon and \Delta(1232).
We work to third order in a small scale expansion with both and
treated as light scales. We note that in the region,
straightward power counting breaks as the amplitudes become very large, to deal
with this problem, we suggest that the appropriate way to compare theoretical
calculations with experimental data is via weighted integrals of the amplitudes
through the region.Comment: 34 pages and 5 figures,new counterterms arr adde
Strangeness production in proton-proton and proton-nucleus collisions
In these lectures we discuss the investigation of the strange meson
production in proton-proton () and in proton-nucleus () reactions
within an effective Lagrangian model. The kaon production proceeds mainly via
the excitations of (1650), (1710), and (1720) resonant
intermediate nucleonic states, in the collision of two initial state nucleons.
Therefore, the strangeness production is expected to provide information about
the resonances lying at higher excitation energies. For beam energies very
close to the kaon production threshold the hyperon-proton final state
interaction effects are quite important. Thus, these studies provide a check on
the models of hyperon-nucleon interactions. The in-medium production of kaons
show strong sensitivity to the self energies of the intermediate mesons.Comment: 16 pages, 9 figures, Talk presented in the workshop on Hadron
Physics, Puri, India, March 7-17,200