222 research outputs found
Analysis of the low-energy differential cross sections of the CHAOS Collaboration
This paper presents the results of an analysis of the low-energy
differential cross sections, acquired by the CHAOS Collaboration at TRIUMF
\cite{chaos,denz}. We first analyse separately the and the
elastic-scattering measurements on the basis of standard low-energy
parameterisations of the - and p-wave -matrix elements. After the removal
of the outliers, we subject the truncated elastic-scattering
databases into a common optimisation scheme using the ETH model \cite{glmbg};
the optimisation failed to produce reasonable values for the model parameters.
We conclude that the problems we have encountered in the analysis of these data
are due to the shape of the angular distributions of their
differential cross sections
Analysis of the low-energy charge-exchange data
We analyse the charge-exchange (CX) measurements
below pion laboratory kinetic energy of 100 MeV. After the removal of five
degrees of freedom from the initial database, we combine it with the truncated
database of Ref. \cite{mrw1} and fit the ETH model \cite{glmbg} to
the resulting data. The set of the parameter values of the ETH model, as well
as the predictions derived on their basis for the hadronic phase shifts and for
the low-energy constants, are significantly different from the results
obtained in the analysis of the truncated elastic-scattering
databases. The main difference in the hadronic phase shifts occurs in
. We discuss the implications of these findings in
terms of the violation of the isospin invariance in the hadronic part of the
interaction. The effect observed amounts to the level of in the
CX scattering amplitude below 70 MeV. The results and conclusions of this study
agree well with those obtained in the mid 1990s, when the isospin invariance
was first tested by using experimental data, and disagree with the
predictions obtained within the framework of the heavy-baryon
Chiral-Perturbation Theory
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