2,000 research outputs found
Extracting the photoproduction cross section off the neutron gn-->pi-p from deuteron data with FSI effects
The incoherent pion photoproduction reaction gd-->pi-pp is considered
theoretically in a wide energy region Eth =< Eg =< 2700 MeV. The model applied
contains the impulse approximation as well as the NN- and piN-FSI amplitudes.
The aim of the paper is to study a reliable way for getting the information on
elementary gn-->pi-p reaction cross section beyond the impulse approximation
for gd-->pi-pp. For the elementary gN-->piN, NN-->NN, and piN-->piN amplitudes,
the results of the GW DAC are used. There are no additional theoretical
constraints. The calculated cross section dSigma/dOmega(gd->pi-pp) are compared
with existing data. The procedure used to extract information on the
differential cross section dSigma/dOmega(gn-->pi-p) on the neutron from the
deuteron data using the FSI correction factor R is discussed. The calculations
for R versus pi-p CM angle \theta_1 of the outgoing pion are performed at
different photon-beam energies with kinematical cuts for "quasi-free" process
gn-->pi-p. The results show a sizeable FSI effect R \neq 1 from S-wave part of
pp-FSI at small angles close to \theta_1 ~ 0: this region narrows as the photon
energy increases. At larger angles, the effect is small (|R-1|<<1) and agrees
with estimations of FSI in the Glauber approach.Comment: 28 pages, 5 figures, 1 tabl
Evaluation of the gn-->pi-p differential cross sections in the Delta-isobar region
Differential cross sections for the process gn-->pi-p have been extracted
from MAMI-B measurements of gd-->pi-pp, accounting for final-state interaction
effects, using a diagrammatic technique taking into account the NN and piN
final-state interaction amplitudes. Results are compared to previous
measurements of the inverse process, pi-p--> ng, and recent multipole analyses.Comment: 6 pages, 4 figures. v2: Further clarifications and minor changes. A
new figure inserte
Updated analysis of NN elastic scattering to 3 GeV
A partial-wave analysis of NN elastic scattering data has been updated to
include a number of recent measurements. Experiments carried out at the Cooler
Synchrotron (COSY) by the EDDA Collaboration have had a significant impact
above 1 GeV. Results are discussed in terms of the partial-wave and
direct-reconstruction amplitudes.Comment: 16 pages, 14 figures, 2 tables; Fig 10 error corrected; Accepted for
publication in Physical Review
On the Extraction of Cross Sections for pi0 and eta Photoproduction off Neutrons from Deuteron Data
We discuss the procedure of extracting the photoproduction cross section for
neutral pseudoscalar mesons off neutrons from deuteron data. The main statement
is that the final-state interaction (FSI) corrections for the proton and
neutron target are in general not equal, but for pi0 production there are
special cases were they have to be identical and there are large regions in the
parameter space of incident photon energy and pion polar angle, \theta^*, where
they happen to be quite similar. The corrections for both target nucleons are
practically identical for production in the energy range of the
Delta(1232)3/2+ resonance due to the specific isospin structure of this
excitation. Also above the -isobar range large differences between
proton and neutron correction factors are only predicted for extreme forward
angles ( < 20 deg), but the results are similar for larger angles.
Numerical results for the gp-->pi0p and gn-->pi0n correction factors are
discussed. Also the model description for the available data on the
differential gd-->pi0pn cross sections are given.Comment: 16 pages, 5 figures; v2 fixed several minor typo
Helicity-dependent photoabsorption cross sections on the nucleon
We examine the energy dependence of single-meson photoproduction as it
contributes to the Gerasimov-Drell-Hearn (GDH) sum rule. For photon energies
above approximately 1 GeV, through the full resonance region, this contribution
dominates the proton sum rule integral. Over the same energy region, our
single-pion contribution to the neutron sum rule also qualitatively follows a
recent set of GDH data. The predicted neutral-pion contribution to the neutron
sum rule is nearly zero above 1 GeV in this result. The SAID and Mainz (MAID)
results are very different for a number of observables over this energy region.Comment: 7 pages, 5 figur
Observation of a narrow structure in p(gamma,K_s)X via interference with phi-meson production
We report observation of a narrow peak structure at ~1.54 GeV with a Gaussian
width sigma=6 MeV in the missing of K_s in the reaction gamma+p = pK_sK_L. The
observed structure may be due to the interference between a strange (or
anti-strange) baryon resonance in the pK_L system and the phi(K_sK_L)
photoproduction leading to the same final state. The statistical significance
of the observed excess of events estimated as the log likelihood ratio of the
resonant signal+background hypothesis and the phi-production based background
only hypothesis corresponds to 5.3 sigma.Comment: Accepted for publication in Physical Review C, 9 pages, 11 figures, 1
table added, revise
Properties of the Resonance Lambda(1520) as seen in the Forward Electroproduction at JLab Hall A
High-resolution spectrometer measurements of the reaction H(e,e' K+)X at
small Q2 are used to extract the mass and width of the Lambda(1520). We
investigate dependence of the resonance parameters on different
parametrizations of the background and the resonance peak itself. Our final
values for the Breit-Wigner parameters are M=1520.4+-0.6(stat)+-1.5(syst) MeV
and Gamma=18.6+-1.9(stat)+-1(syst) MeV. The width appears to be more sensitive
to the assumptions than the mass. We also estimate, for the first time, the
pole position for this resonance and find that both the pole mass and width
seem to be smaller than their Breit-Wigner values.Comment: 4 pages, 1 figure, to appear in the proceedings of MENU 201
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