10 research outputs found
A resonance interpretation for the nonmonotonic behavior of the phi-photoproduction cross section near threshold
We study whether the nonmonotonic behavior found in the differential cross
section of the phi-meson photoproduction near threshold can be described by a
resonance. The resonant contribution is evaluated by using an effective
Lagrangian approach. We find that, with the assumption of a J^P=3/2^- resonance
with mass of 2.10 \pm 0.03 GeV and width of 0.465 \pm 0.141 GeV, LEPS data can
indeed be well described. The ratio of the helicity amplitudes A_1/2/A_3/2
calculated from the resulting coupling constants differs in sign from that of
the known D13(2080). We further find that the addition of this postulated
resonance can substantially improve the agreement between the existing
theoretical predictions and the recent omega photoproduction data if a large
value of the OZI evading parameter x_OZI = 12 is assumed for the resonance.Comment: Contribution to the Proceedings of BARYONS'10 - International
conference on the structure of baryons, Dec. 7-11, 2010, Osaka, Japa
The strangeness form factors of the proton within nonrelativistic constituent quark model revisited
We reexamine, within the nonrelativistic constituent quark model (NRCQM), a
recent claim that the current data on the strangeness form factors indicates
that the uuds\bar{s} component in the proton is such that the uuds subsystem
has the mixed spatial symmetry [31]_X and flavor spin symmetry
[4]_{FS}[22]_F[22]_S, with \bar{s} in S state (configuration I). We find this
claim to be invalid if corrected expressions for the contributions of the
transition current to G_A^s and G_E^s are used. We show that, instead, it is
the lowest-lying uuds\bar{s} configuration with uuds subsystem of completely
symmetric spatial symmetry [4]_X and flavor spin symmetry [4]_{FS}[22]_F[22]_S,
with \bar{s} in P state (configuration II), which could account for the
empirical signs of all form factors G_E^s, G_M^s, and G_A^s. Further, we find
that removing the center-of-mass motion of the clusters will considerably
enhance the contributions of the transition current. We also demonstrate that
it is possible to give a reasonable description of the existing form factors
data with a tiny probability P_{s\bar{s}}=0.025% for the uuds\bar{s} component.
We further see that with a small admixture of configuration I, the agreement of
our prediction with data for G_A^s at low-q^2 region can be markedly improved.
We find that without removing CM motion, P_{s\bar{s}} would be overestimated by
about a factor of four in the case when transition current dominates. We also
explore the consequence of a recent estimate reached from analyzing existing
data on \bar{d} -\bar{u}, s +\bar{s}, and \bar{u} + \bar{d} - s -\bar{s}, that
P_{s\bar{s}} lies between 2.4-2.9%. It would lead to a large size for the
five-quark system and a small bump in both G_E^s+\eta G_M^s and G_E^s in the
region of q^2<=0.1 GeV^2 within the considered model.Comment: 6 pages, 2 figure
Model Dependence of the Properties of S11 Baryon Resonances
The properties of baryon resonances are extracted from a complicated process
of fitting sophisticated, empirical models to data. The reliability of this
process comes from the quality of data and the robustness of the models
employed. With the large of amount of data coming from recent experiments, this
is an excellent time for a study of the model dependence of this extraction
process. A test case is chosen where many theoretical details of the model are
required, the S11 partial wave. The properties of the two lowest N* resonances
in this partial wave are determined using various models of the resonant and
non-resonant amplitudes.Comment: 24 pages, 10 figures; revised fits with error estimates, expanded
comparison between CMB and K-matrix model
Proton strangeness form factors in (4,1) clustering configurations
We reexamine a recent result within a nonrelativistic constituent quark model
(NRCQM) which maintains that the uuds\bar s component in the proton has its
uuds subsystem in P state, with its \bar s in S state (configuration I). When
the result are corrected, contrary to the previous result, we find that all the
empirical signs of the form factors data can be described by the lowest-lying
uuds\bar s configuration with \bar s in P state that has its uuds subsystem in
state (configuration II). Further, it is also found that the removal of the
center-of-mass (CM) motion of the clusters will enhance the contributions of
the transition current considerably. We also show that a reasonable description
of the existing form factors data can be obtained with a very small probability
P_{s\bar s}=0.025% for the uuds\bar s component. We further see that the
agreement of our prediction with the data for G_A^s at low-q^2 region can be
markedly improved by a small admixture of configuration I. It is also found
that by not removing CM motion, P_{s\bar s} would be overestimated by about a
factor of four in the case when transition dominates over direct currents.
Then, we also study the consequence of a recent estimate reached from analyzing
the existing data on quark distributions that P_{s\bar s} lies between 2.4-2.9%
which would lead to a large size for the five-quark (5q) system, as well as a
small bump in both G^s_E+\eta G^s_M and G^s_E in the region of q^2 =< 0.1
GeV^2.Comment: Prepared for The Fifth Asia-Pacific Conference on Few-Body Problems
in Physics 2011 in Seoul, South Korea, 22-26 August 201
Incoherent photoproduction of ϕ-meson from deuteron at low energies
The LEPS and CLAS data of the incoherent photoproduction of ϕ meson from deuteron at low energies are studied with a model for ϕ meson photoproduction from nucleon consisting of Pomeron, π, and η meson exchanges in the t-channel, and a postulated resonance, with parameters fitted to recent LEPS data on ϕ production from proton near threshold. The resonance was introduced to explain an observed bump in the forward differential cross section. Within impulse approximation, we find that the Fermi motion, final state interaction, and the resonance excitation all give important contributions to improve the agreement with data. However, discrepancies remain. Contributions from ϕ production via spectator nucleon by other mesons like π,ρ, and ϕ produced from the first nucleon need to be calculated in order to gain insight on the medium effects as well as the existence of the postulated nucleon resonance