92 research outputs found
An isotopic effect in phi photoproduction at a few GeV
A distinct isotopic effect in phi photoproduction at 2-5 GeV region is
identified by examining the production amplitudes due to Pomeron-exchange and
meson-exchange mechanisms. This effect is mainly caused by the pi-eta
interference constrained by SU(3) symmetry and the isotopic structure of the
gamma NN coupling in the direct phi-radiation amplitude. It can be tested
experimentally by measuring differences in the polarization observables between
the gamma-p and gamma-n reactions.Comment: 11 pages, 6 figure
Coherent Photoproduction of Eta-Mesons on Spin-Zero Nuclei in a Relativistic, Non-local Model
The coherent photoproduction of -mesons on spin-zero nuclei is studied
in a relativistic, non-local model, which we have previously applied to the
coherent photoproduction of pions. We find that different off-shell
extrapolations of the elementary production operator lead to large effects in
the cross section. We also show that the almost complete suppression of the
N(1535) seen in earlier studies on this reaction is a result of the local or
factorization approximation used in these works. Non-local effects can lead to
a considerable contribution from this resonance. The relative size of the
N(1535) contribution depends on the structure of the nucleus under
consideration. We give an estimate for the contribution of the N(1520)
resonance and discuss the effect of an -nucleus optical potentialComment: 29 pages, 14 figures; slight changes in presentation, extended
discussion, one new figur
The size of the proton - closing in on the radius puzzle
We analyze the recent electron-proton scattering data from Mainz using a
dispersive framework that respects the constraints from analyticity and
unitarity on the nucleon structure. We also perform a continued fraction
analysis of these data. We find a small electric proton charge radius, r_E^p =
0.84_{-0.01}^{+0.01} fm, consistent with the recent determination from muonic
hydrogen measurements and earlier dispersive analyses. We also extract the
proton magnetic radius, r_M^p = 0.86_{-0.03}^{+0.02} fm, consistent with
earlier determinations based on dispersion relations.Comment: 4 pages, 2 figures, fit improved, small modifications, section on
continued fractions modified, conclusions on the proton charge radius
unchanged, version accepted for publication in European Physical Journal
Realistic Few-Body Physics in the Reaction
We use realistic two- and three-nucleon interactions in a hybrid
chiral-perturbation-theory calculation of the charge-symmetry-breaking reaction
to show that a cross section of the experimentally measured
size can be obtained using LO and NNLO pion-production operators. This result
supports the validity of our power counting scheme and demonstrates the
necessity of using an accurate treatment of ISI and FSI.Comment: 11 pages, 1 figur
Role of Vector Mesons in High-Q^2 Lepton-Nucleon Scattering
The possible role played by vector mesons in inclusive deep inelastic
lepton-nucleon scattering is investigated. In the context of the convolution
model, we calculate self-consistently the scaling contribution to the nucleon
structure function using the formalism of time-ordered perturbation theory in
the infinite momentum frame. Our results indicate potentially significant
effects only when the vector meson---nucleon form factor is very hard.
Agreement with the experimental antiquark distributions, however, requires
relatively soft form factors for the , and vertices.Comment: 22 pages, 9 figures (available upon request); accepted for
publication in Phys.Rev.D, ADP-92-197/T12
Effective Lagrangian Approach to the Theory of Eta Photoproduction in the Region
We investigate eta photoproduction in the resonance region
within the effective Lagrangian approach (ELA), wherein leading contributions
to the amplitude at the tree level are taken into account. These include the
nucleon Born terms and the leading -channel vector meson exchanges as the
non-resonant pieces. In addition, we consider five resonance contributions in
the - and - channel; besides the dominant , these are:
and . The amplitudes for the
and the photoproduction near threshold have significant
differences, even as they share common contributions, such as those of the
nucleon Born terms. Among these differences, the contribution to the
photoproduction of the -channel excitation of the is the most
significant. We find the off-shell properties of the spin-3/2 resonances to be
important in determining the background contributions. Fitting our effective
amplitude to the available data base allows us to extract the quantity
, characteristic of the
photoexcitation of the resonance and its decay into the
-nucleon channel, of interest to precise tests of hadron models. At the
photon point, we determine it to be from
the old data base, and from a
combination of old data base and new Bates data. We obtain the helicity
amplitude for to be from the old data base, and from the combination of the old data base and new Bates
data, compared with the results of the analysis of pion photoproduction
yielding , in the same units.Comment: 43 pages, RevTeX, 9 figures available upon request, to appear in
Phys. Rev.
The high-precision, charge-dependent Bonn nucleon-nucleon potential (CD-Bonn)
We present a charge-dependent nucleon-nucleon (NN) potential that fits the
world proton-proton data below 350 MeV available in the year of 2000 with a
chi^2 per datum of 1.01 for 2932 data and the corresponding neutron-proton data
with chi^2/datum = 1.02 for 3058 data. This reproduction of the NN data is more
accurate than by any phase-shift analysis and any other NN potential. The
charge-dependence of the present potential (that has been dubbed `CD-Bonn') is
based upon the predictions by the Bonn Full Model for charge-symmetry and
charge-independence breaking in all partial waves with J <= 4. The potential is
represented in terms of the covariant Feynman amplitudes for one-boson exchange
which are nonlocal. Therefore, the off-shell behavior of the CD-Bonn potential
differs in a characteristic and well-founded way from commonly used local
potentials and leads to larger binding energies in nuclear few- and many-body
systems, where underbinding is a persistent problem.Comment: 69 pages (RevTex) including 20 tables and 9 figures (ps files
production in proton-proton scattering close to threshold}
The (958) reaction has been measured at COSY using
the internal beam and the COSY-11 facility. The total cross sections at the
four different excess energies \mbox{
and } have been evaluated to be \mbox{,
, , ~ and },
respectively. In this region of excess energy the (958) cross
sections are much lower compared to those of the and
production.Comment: 11 pages, 3 figure
Silicon Electronic Photonic Integrated Circuits for High Speed Analog to Digital Conversion
Abstract: Integrated optical components on the silicon platform and optically enhanced electronic sampling circuits are demonstrated that enable the fabrication of a variety of electronic-photonic A/D converter chips surpassing currently available technology in sampling speed and resolution
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