630 research outputs found
A model-independent analysis of final-state interactions in \bar B_{d/s}^0 --> J/psi pi pi
Exploiting -meson decays for Standard Model tests and beyond requires a
precise understanding of the strong final-state interactions that can be
provided model-independently by means of dispersion theory. This formalism
allows one to deduce the universal pion-pion final-state interactions from the
accurately known phase shifts and, in the scalar sector, a
coupled-channel treatment with the kaon-antikaon system. In this work an
analysis of the decays and is presented. We find very good agreement with the data up
to 1.05 GeV with a number of parameters reduced significantly compared to a
phenomenological analysis. In addition, the phases of the amplitudes are
correct by construction, a crucial feature when it comes to studies of
violation in heavy-meson decays.Comment: 25 pages, 6 figures, version published in JHE
Towards a field theoretic understanding of NN->NNpi
We study the production amplitude for the reaction NN->NNpi up to
next--to--leading order in chiral perturbation theory using a counting scheme
that takes into account the large scale introduced by the initial momentum. In
particular we investigate a subtlety that arises once the leading loop
contributions are convoluted with the NN wavefunctions as demanded by the
non--perturbative nature of the NN interaction. We show how to properly
identify the irreducible contribution of loop diagrams in such type of
reaction. The net effect of the inclusion of all next-to-leading order loops is
to enhance the leading rescattering amplitude by a factor of 4/3, bringing its
contribution to the cross section for pp->dpi+ close to the experimental value.Comment: 15 Pages, 5 Figure
N_c and m_pi dependence of rho and sigma mesons from unitarized Chiral Perturbation Theory
We review our work on the rho and sigma resonances derived from the Inverse
Amplitude Method. In particular, we study the leading 1/N_c behavior of the
resonances masses and widths and their evolution with changing m_pi. The 1/N_c
expansion gives a clear definition of quark-antiquark states, which is neatly
satisfied by the rho but not by the sigma, showing that its dominant component
is not quark-antiquark. The m_pi dependence of the resonance properties is
relevant to connect with lattice studies. We show that our predictions compare
well with some lattice results and we find that the rho-pi-pi coupling constant
is m_pi independent, in contrast with the sigma-pi-pi coupling, that shows a
strong m_pi dependence.Comment: To appear in the Proceedings of the Chiral10 Workshop, June 21-24
2010. Valencia, Spai
Charge symmetry breaking as a probe for the real part of eta--nucleus scattering lengths
We demonstrate that one can use the occurrence of charge symmetry breaking as
a tool to explore the eta--nucleus interaction near the eta threshold. Based on
indications that the cross section ratio of pi+ and pi0 production on nuclei
deviates from the isotopic value in the vicinity of the eta production
threshold, due to, e.g., pi0-eta mixing, we argue that a systematic study of
this ratio as a function of the energy would allow to pin down the sign of the
real part of the eta-nucleus scattering length. This sign plays an important
role in the context of the possible existence of eta-nucleus bound states.Comment: 4 pages, 1 figur
Polarization phenomena in the reaction NN to NNpi near threshold
First calculations for spin-dependent observables of the reactions , and near threshold are presented,
employing the J\"ulich model for pion production. The influence of resonant
(via the excitation of the ) and non-resonant p-wave pion
production mechanisms on these observables is examined. For the reactions and nice agreement of our predictions with the
presently available data on spin correlation coefficents is observed whereas
for the description of the data is less satisfying.Comment: 10 pages, 4 figure
Near threshold Lambda and Sigma production in pp collisions
A model calculation for the reactions and near their thresholds is presented. It is argued that the experimentally
observed strong suppression of production compared to
production at the same excess energy could be due to a destructive interference
between the and exchange contributions in the reaction . Predictions for and
are given.Comment: 3 pages, 1 figure, uses espcrc1.sty, contribution presented at the
16th International Conference on Few-Body Problems in Physics, Taipei,
Taiwan, 6-10 March 200
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