13,176 research outputs found
Three body resonances in two meson-one baryon systems
We report four 's and three 's, in the 1500 - 1800 MeV
region, as two meson - one baryon S-wave resonances. We solve Faddeev
equations in the coupled channel approach. The invariant mass of one of the
meson-baryon pairs and that of the three particles have been varied and peaks
in the squared three body -matrix have been found very close to the existing
= -1, low lying baryon resonances. The input two-body
-matrices for meson-meson and meson-baryon interaction have been calculated
by solving the Bethe-Salpeter equation with the potentials obtained in the
chiral unitary approach.Comment: corrected version, new channels evaluated, new references adde
Study of the system using QCD sum rules
In this talk I present a study of the system made by using the
method of QCD sum rules. Considering isospin and spin projectors, we
investigate the different configurations and obtain three mesons with
isospin , spin , , and with masses MeV,
MeV, and MeV, respectively. The last state can be
related to (spin 2) listed by the Particle Data Group, while one
of the first two might be associated with , whose spin-parity is
unknown. In the case of we also find evidences of three states with
spin 0, 1 and 2, respectively, with masses MeV, MeV,
and MeV.Comment: Contribution to the proceedings of the XXXVI Reuni\~ao de Trabalho
sobre F\'isica Nuclear no Brasil, Maresias, S\~ao Paulo, Brazi
A study of the - coupled systems
We study the strangeness meson-baryon systems to obtain improved
and amplitudes and to look for a possible resonance formation by the
- coupled interaction. We obtain amplitudes for light vector
meson-baryon systems by implementing the -, -, - channel diagrams and
a contact interaction. The pseudoscalar meson-baryon interactions are obtained
by relying on the Weinberg-Tomozawa theorem. The transition amplitudes between
the systems consisting of pseudoscalars and vector mesons are calculated by
extending the Kroll-Ruderman term for pion photoproduction replacing the photon
by a vector meson. We fix the subtraction constants required to calculate the
loops by fitting our amplitudes to the data available for the isospin 0
and 1 -wave phase shifts. We provide the scattering lengths and the total
cross sections for the and systems obtained in our model, which
can be useful in future in-medium calculations. Our amplitudes do not
correspond to formation of any resonance in none of the isospin and spin
configurations.Comment: Published version, sent to avoid confusions recently noticed by
author
On the absorption and production cross sections of and
We have computed the isospin and spin averaged cross sections of the
processes and , which are crucial in the
determination of the abundances of and in heavy ion collisions.
Improving previous calculations, we have considered several mechanisms which
were missing, such as the exchange of axial and vector resonances (,
, , etc...) and also other processes such as and . We find that
some of these mechanisms give important contributions to the cross section. Our
results also suggest that, in a hadron gas, production might be more
important than its absorption
production and absorption in a hot hadron gas
We calculate the time evolution of the abundance in the hot hadron
gas produced in the late stage of heavy ion collisions. We use effective field
Lagrangians to obtain the production and dissociation cross sections of
. In this evaluation we include diagrams involving the anomalous
couplings and and also the
couplings of the with charged and mesons. With these new
terms the interaction cross sections are much larger than those found
in previous works. Using these cross sections as input in rate equations, we
conclude that during the expansion and cooling of the hadronic gas, the number
of , originally produced at the end of the mixed QGP/hadron gas phase,
is reduced by a factor of 4.Comment: 8 pages, 4 figure
Three body systems with strangeness and exotic systems
We report on four 's and three 's, in the 1500 - 1800 MeV
region, as two meson - one baryon S-wave resonances found by solving
the Faddeev equations in the coupled channel approach, which can be associated
to the existing = -1, low lying baryon resonances. On the
other hand we also report on a new, hidden strangeness state, mostly made
of , with mass around 1920 MeV, which we think could be
responsible for the peak seen in the around this
energy. Finally we address a very novel topic in which we show how few body
systems of several mesons can be produced, with their spins aligned up
to J=6, and how these states found theoretically can be associated to several
known mesons with spins J=2,3,4,5,6.Comment: Talk at the 21st European Conference on Few Body Problems in Physics,
Salamanca, Sep. 201
Interpreting the peak structures around 1800 MeV in the BES data on ,
In this talk we present an interpretation for the experimental data available
on two different processes, namely, , , which seem to indicate existence of two new resonances
with the same quantum numbers () and very similar mass
(~1800 MeV) but with very different decay properties. However, our studies show
that the peak structure found in the invariant mass, in , is a manifestation of the well known while
the cross section enhancement found in is indeed
a new resonance with mass near 1800 MeV. We present an explanation for
the different decay properties of these two scalar resonances.Comment: Proceedings for the nuclear physics meeting ("XXXVI Reuni\~ao de
trabalho sobre f\'isica nuclear no Brasil") held in Maresias during Sept.
1-5. To be published as AIP proceeding
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