3,393 research outputs found
Comment on The Evidence for a Pentaquark and Kinematic Reflections
The Regge exchange model used by Dzierba et al. is shown to be questionable,
since the pion pole term is not allowed. Hence the Regge amplitudes in their
calculation are exaggerated. The amount of kinematic reflection in the mass
spectrum of the (nK+) system, which is one decay channel of a possible
pentaquark, is not well justified in the fitting procedure used by Dzierba et
al., as shown by comparison with the (K+K-) invariant mass spectrum, which is
one decay channel of the a_2 and f_2 tensor mesons. While kinematic reflections
are still a concern in some papers that have presented evidence for the
pentaquark, better quantitative calculations are needed to demonstrate the
significance of this effect.Comment: Comment submitted to Phys. Rev. D (no figures
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
Kink-antikink interactions in the double sine-Gordon equation and the problem of resonance frequencies
We studied the kink-antikink collision process for the "double sine-Gordon"
(DSG) equation in 1+1 dimensions at different values of the potential parameter
. For small values of we discuss the problem of resonance frequencies.
We give qualitative explanation of the frequency shift in comparison with the
frequency of the discrete level in the potential well of isolated kink. We show
that in this region of the parameter the effective long-range interaction
between kink and antikink takes place.Comment: 9 pages, LaTeX, 4 figures (eps
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
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