305 research outputs found

### Photoproduction of Pseudoscalar Mesons

Experiments that study the photoproduction of pseudoscalar mesons; pions,
etas and kaons, have the potential to increase our knowledge of baryon and
hyperon resonance properties. Recent experiments at JLab, Mainz, GRAAL, and
Bonn are beginning to produce results in the form of polarization and asymmetry
measurements and determinations of the differential and integrated cross
sections. These new data are essential to the performance of Partial-Wave
Analyses that are less model dependent and coupled-channels calculations that
incorporate unitarity dynamically,combining hadronic reaction channels together
with electromagnetic processes. This approach is necessary to extract resonance
properties and may lead to the identification of missing, but predicted,
resonances. Some recent experimental and phenomenological results for single
and double pseudoscalar meson photoproduction are discussed.Comment: 4 pages, 4 figures, Proceedings of Particles and Nuclei, PANIC2002,
Osaka, Japan, Sept.30-Oct.4, 200

### Extraction of the $\pi NN$ coupling constant from NN scattering data

We reexamine Chew's method for extracting the $\pi NN$ coupling constant from
np differential cross section measurements. Values for this coupling are
extracted below 350 MeV, in the potential model region, and up to 1 GeV. The
analyses to 1~GeV have utilized 55 data sets. We compare these results to those
obtained via $\chi^2$ mapping techniques. We find that these two methods give
consistent results which are in agreement with previous Nijmegen
determinations.Comment: 12 pages of text plus 2 figures. Revtex file and postscript figures
available via anonymous FTP at ftp://clsaid.phys.vt.edu/pub/n

### Model dependence of single-energy fits to pion photoproduction data

Model dependence of multipole analysis has been explored through
energy-dependent and single-energy fits to pion photoproduction data. The MAID
energy-dependent solution has been used as input for an event generator
producing realistic pseudo data. These were fitted using the SAID
parametrization approach to determine single-energy and energy-dependent
solutions over a range of lab photon energies from 200 to 1200 MeV. The
resulting solutions were found to be consistent with the input amplitudes from
MAID. Fits with a $\chi$-squared per datum of unity or less were generally
achieved. We discuss energy regions where consistent results are expected, and
explore the sensitivity of fits to the number of included single- and
double-polarization observables. The influence of Watson's theorem is examined
in detail.Comment: 12 pages, 8 figure

### Multipole Amplitudes of Pion Photoproduction on Nucleons up to 2GeV within Dispersion Relations and Unitary Isobar Model

Two approaches for analysis of pion photo- and electroproduction on nucleons
in the resonance energy region are checked at $Q^2=0$ using the results of
GWU(VPI) partial-wave analysis of photoproduction data. The approaches are
based on dispersion relations and unitary isobar model. Within dispersion
relations good description of photoproduction multipoles is obtained up to
$W=1.8 GeV$. Within unitary isobar model, modified with increasing energy by
incorporation of Regge poles, and with unified Breit-Wigner parametrization of
resonance contributions, good description of photoproduction multipoles is
obtained up to $W=2 GeV$.Comment: 23 pages, LaTe

### Coherent bubble-sum approximation for coupled-channel resonance scattering

For coupled-channel resonance scattering we derive a model with a closed form
solution for the $T$-matrix that satisfies unitarity and analyticity. The
two-channel case is handled explicitly for an arbitrary number of resonances.
The method focuses on the expansion of the transition matrix elements,
$\Gamma(s)$, in known analytical functions. The appropriate hadronic form
factors and the related energy shifts can be determined from the scattering
data. The differences between this method and the $K$-matrix and the
Breit-Wigner approximation are illustrated in the case of the $S_{11}$
resonances $S_{11}(1535)$ and $S_{11}(1650)$.Comment: 8 pages, 1 figure, code available from
http://www.phyast.pitt.edu/~norbertl/bubblegum2

### Angle-dependent normalization of neutron-proton differential cross sections

Systematic errors in the database of $np$ differential cross sections below
350 MeV are studied. By applying angle-dependent normalizations with the help
of the energy-dependent Nijmegen partial-wave analysis PWA93 the
$\chi^2$-values of some seriously flawed data sets can be reduced significantly
at the expense of a few degrees of freedom. It turns out that in these special
cases the renormalized data sets can be made statistically acceptable such that
they do not have to be discarded any longer in partial-wave analyses of the
two-nucleon scattering data.Comment: 11 pages, 1 figure; expanded versio

### Delta rho pi interaction leading to N* and Delta* resonances

We have performed a calculation for the three body $\Delta \rho \pi$ system
by using the fixed center approximation to Faddeev equations, taking the
interaction between $\Delta$ and $\rho$, $\Delta$ and$\pi$, and $\rho$ and
$\pi$ from the chiral unitary approach. We find several peaks in the modulus
squared of the three-body scattering amplitude, indicating the existence of
resonances, which can be associated to known $I=1/2, 3/2$ and $J^P=1/2^+,
3/2^+$ and $5/2^+$ baryon states.Comment: Presented at the 21st European Conference on Few-Body Problems in
Physics, Salamanca, Spain, 30 August - 3 September 201

### On the pion-nucleon coupling constant

In view of persisting misunderstanding about the determination of the
pion-nucleon coupling constants in the Nijmegen multienergy partial-wave
analyses of pp, np, and pbar-p scattering data, we present additional
information which may clarify several points of discussion. We comment on
several recent papers addressing the issue of the pion-nucleon coupling
constant and criticizing the Nijmegen analyses.Comment: 19 pages, Nijmegen preprint THEF-NYM-92-0

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