58 research outputs found
Photoproduction of Pentaquark in Feynman and Regge Theories
Photoproduction of the Theta+ pentaquark on the proton is analyzed by using
an isobar and a Regge models. The difference in the calculated total cross
section is found to be more than two orders of magnitude for a hadronic form
factor cut-off Lambda > 1 GeV. Comparable results would be obtained for 0.6 <
Lambda < 0.8 GeV. We also calculate contribution of the Theta+ photoproduction
to the GDH integral. By comparing with the current phenomenological
calculation, it is found that the GDH sum rule favors the result obtained from
Regge approach and isobar model with small Lambda.Comment: 5 pages, 5 figures, submitted to Phys.Rev.C as a Rapid Communicatio
Kaon and Hyperon Form Factors in Kaon Electroproduction on the Nucleon
The electromagnetic form factors of strange mesons and baryons are studied by
means of kaon electroproduction on the nucleon. The response functions that are
sensitive to the K0, Lambda, Sigma, and KK*\gamma transition form factors are
systematically explored. The effects of these form factors on several response
functions are discussed.Comment: 10 pages, Latex2e, 12 postscript figures. Invited talk given at the
International Conference on Hypernuclear and Strange Particle Physics
(HYP97), Brookhaven National Laboratory, USA, October 13-18, 1997. To be
published in Nucl. Phys.
Rescattering effects in coherent eta-photoproduction on the deuteron
Rescattering effects in coherent eta photoproduction on the deuteron are
studied in the region of the S_11(1535) resonance. For the elementary reaction
mechanism on the nucleon, an effective isobar model with inclusion of
resonances and Born terms is used. The resonance parameters are fixed by
considering pion photoproduction only. For the coherent eta production on the
deuteron we have considered the impulse approximation taking into account the
P_11(1440), D_13(1520), and S_11(1535) resonances, rescattering, and meson
exchange currents. For the rescattering mechanism a coupled channel model
including the dominant S_11(1535) resonance is used.Comment: 8 pages LaTeX using revtex, 6 postscript figures (using epsf.sty
Analysis of resonance multipoles from polarization observables in eta photoproduction
A combined analysis of new eta photoproduction data for total and
differential cross sections, target asymmetry and photon asymmetry is
presented. Using a few reasonable assumptions we perform the first
model-independent analysis of the E0+, E2- and M2- eta photoproduction
multipoles. Making use of the well-known A3/2 helicity amplitude of the
D13(1520) state we extract its branching ratio to the eta-N channel,
Gamma(eta,N)/Gamma = (0.08 +- 0.01)%. At higher energies, we show that the
photon asymmetry is extremely sensitive to small multipoles that are excited by
photons in the helicity 3/2 state. The new GRAAL photon asymmetry data at
higher energy show a clear signal of the F15(1680) excitation which permits
extracting an F15(1680)->eta,N branching ratio of (0.15 +0.35 -0.10)%.Comment: 14 pages of LATEX including 7 postscript figure
Kaon photoproduction on the nucleon: Contributions of kaon-hyperon final states to the magnetic moment of the nucleon
By using the Gerasimov-Drell-Hearn (GDH) sum rule and an isobaric model of
kaon photoproduction, we calculate contributions of kaon-hyperon final states
to the magnetic moment of the proton and the neutron. We find that the
contributions are small. The approximation of sigma_{TT'} by sigma_{T} clearly
overestimates the value of the GDH integral. We find a smaller upper bound for
the contributions of kaon-hyperon final states to the proton's anomalous
magnetic moment in kaon photoproduction, and a positive contribution for the
square of the neutron's magnetic moment.Comment: 6 pages, revtex, 1 postscript figure, to appear in Phys. Rev.
The role of chiral loops in
We consider the rare decay and calculate the
non-resonant contribution to the amplitude to one loop in Chiral Perturbation
Theory. We display our result as both a diphoton energy spectrum and a partial
decay rate as a function of the photon energy cut. It turns out that the
one-loop correction can be numerically very important and could be detected, at
sufficiently large center-of-mass photon energies, from a measurement of the
partial decay width.Comment: 10 pages, Latex. Discussion on the resonant background enlarged, sign
error corrected, basic results unchanged. To appear in Phys. Lett.
Coherent eta photoproduction on the deuteron in the resonance region
Coherent eta photoproduction on the deuteron is studied in the
resonance region neglecting eta rescattering and two-body processes. For the
elementary reaction on the nucleon, we have considered the dominant
resonance and as background the nucleon pole terms as well as
and meson exchange. We have studied the influence of different
choices for the neutron resonance amplitude, different prescriptions for fixing
the invariant mass of the resonance amplitude and different methods for
deriving the elementary production amplitude for an arbitrary reference frame.Comment: 33 pages revtex including 13 postscript figure
Low-energy and low-momentum representation of the virtual Compton scattering amplitude
We perform an expansion of the virtual Compton scattering amplitude for low
energies and low momenta and show that this expansion covers the transition
from the regime to be investigated in the scheduled photon electroproduction
experiments to the real Compton scattering regime.
We discuss the relation of the generalized polarizabilities of virtual
Compton scattering to the polarizabilities of real Compton scattering.Comment: 13 pages, LaTeX2e/RevTeX, no figure
Chiral-loop and vector-meson contributions to eta -> pi pi gamma gamma decays
The process eta -> pi0 pi0 gamma gamma is discussed in Chiral Perturbation
Theory (ChPT) extending two recent analyses. Special attention is devoted to
one-loop corrections, eta-eta' mixing effects and vector-meson dominance of
ChPT counter-terms. The less interesting eta -> pi^+ pi^- gamma gamma
transition is briefly discussed too.Comment: 15 pages, 3 Postscript figures, uses epsfig.st
Generalized polarizabilities and the spin-averaged amplitude in virtual Compton scattering off the nucleon
We discuss the low-energy behavior of the spin-averaged amplitude of virtual
Compton scattering (VCS) off a nucleon.
Based on gauge invariance, Lorentz invariance and the discrete symmetries, it
is shown that to first order in the frequency of the final real photon only two
generalized polarizabilities appear.
Different low-energy expansion schemes are discussed and put into
perspective.Comment: 13 pages, 1 postscript figure, Revtex using eps
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