13,310 research outputs found
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
Non-Hermitian robust edge states in one-dimension: Anomalous localization and eigenspace condensation at exceptional points
Capital to topological insulators, the bulk-boundary correspondence ties a
topological invariant computed from the bulk (extended) states with those at
the boundary, which are hence robust to disorder. Here we put forward an
ordering unique to non-Hermitian lattices, whereby a pristine system becomes
devoid of extended states, a property which turns out to be robust to disorder.
This is enabled by a peculiar type of non-Hermitian degeneracy where a
macroscopic fraction of the states coalesce at a single point with geometrical
multiplicity of , that we call a phenomenal point.Comment: 6 pages, 4 figure
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
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
X, Y and Z States
Many new states in the charmonium mass region were recently discovered by
BaBar, Belle, CLEO-c, CDF, D0, BESIII, LHCb and CMS Collaborations. We use the
QCD Sum Rule approach to study the possible structure of some of these states.Comment: Contribution for the proceedings of the "XII Quark Confinement and
the Hadron Spectrum - CONF12" conferenc
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