1,138 research outputs found

### eta nucleus optical potential in a chiral unitary approach

The self-energy of an eta in a nuclear medium is calculated in a chiral
unitary model, and applied to eta states in nuclei. Our calculation predicts an
attractive eta nucleus optical potential which can accommodate many eta bound
states in different nuclei.Comment: 4 pages, 2 figures, Talk given at the XVI International Conference on
Particles and Nucle

### A critical analysis on deeply bound kaonic states in nuclei

We make a critical analysis on the theoretical calculations that lead to
predictions of deeply bound kaonic states in nuclei. The model set-up, after
dropping several important processes and channels, leads unavoidably to an
unrealistic deep potential with a very small imaginary part. We review also the
experimental results taken as reference for the claim of deeply bound kaons. We
suggest that the peaks of the proton spectra come from $K^-$ absorption on a
pair of nucleons, leaving the rest of the nucleons as spectators. Based on this
conjecture we predict what would happen in other nuclei.Comment: 19 pags., 4 figs, version to be published in Phys. Rev.

### The $(\pi^-,\gamma\gamma)$ reaction in nuclei and the $\sigma$ meson in the medium

A theoretical analysis of the $(\pi^-,\gamma\gamma)$ reaction in nuclei is
made in order to find the viability of this reaction to test modifications of
the $\sigma$ meson mass in nuclear matter. The $\pi\pi$ correlation in the
scalar-isoscalar channel in nuclear matter could, in principle, manifest itself
in this reaction since it plays an important role in the
$\pi\pi\to\gamma\gamma$ mechanism. But we conclude that this effect is hardly
visible in this reaction due to the strong background of the
pion-Bremsstrahlung terms. Only with some special cuts and for some
polarization states are the effect visible at the cost of a strong reduction in
the cross section.Comment: 16 pages, 11 figure

### The Y(3940), Z(3930) and the X(4160) as dynamically generated resonances from the vector-vector interaction

We study the vector-vector interaction within the framework of the hidden
gauge formalism for the sector with quantum numbers charm C=0 and strangeness
S=0 in the region around 4000 MeV. We get five poles, three of which could be
identified with the Y(3940), Z(3930) and X(4160). These poles appear with
quantum numbers I=0 and $J^{PC}=0^{++},2^{++}$ and $2^{++}$, respectively, and
can be considered as hadronic molecules made of $D^*\bar{D}^*$,
$D_s^*\bar{D}^*_s$.Comment: to appear in Proceedings of XIII International Conference on Hadron
Spectroscopy, November 29 - December 4, 2009, Florida State Universit

### Improved Fixed Center Approximation of the Faddeev equations for the $\bar{K}NN$ system with S=0

We extend the Fixed Center Approximation (FCA) to the Faddeev Equations for
the $\bar{K} NN$ system with S=0, including the charge exchange mechanisms in
the $\bar{K}$ rescattering which have been ignored in former works within the
FCA. We obtain similar results to those found before, but the binding is
reduced by 6 MeV. At the same time we also evaluate the explicit contribution
the $\pi N \Sigma$ intermediate state in the three body system and find that it
produces and additional small decrease in the binding of about 3 MeV. The
system appears bound by about 35 MeV and the width omitting two body
absorption, is about 50 MeV.Comment: 12 pages, 6 figures. arXiv admin note: substantial text overlap with
arXiv:1102.285

### On the hidden charm pentaquark-s in $\Lambda_b \to J/\psi K^- p$ decay

In a previous work we presented a theoretical analysis of the $\Lambda_b \to
J/\psi K^- p$ reaction from where a recent experiment by the LHCb collaboration
at CERN claimed the existence of two hidden charm pentaquarks, $P_c(4380)^+$
and $P_c(4450)^+$. In that work we focused only on the $\Lambda(1405)$ and
$P_c(4450)^+$ signals and discussed the possible explanation of this pentaquark
state within the picture of a dynamical meson-baryon molecule made up mostly
from $\bar D^* \Sigma_c$ and $\bar D^* \Sigma^*_c$ components. In the present
work we improve upon the previous one by considering the total $K^- p$ and
$J/\psi p$ data including all the relevant resonances contributing to the
spectra, and discuss the possible nature of both $P_c(4380)^+$ and
$P_c(4450)^+$. We also discuss several important topics, like the effect of the
contact term in the reaction, the viability of reproducing the data without the
$P_c(4380)^+$ and the possible quantum numbers assignment to these pentaquarks.Comment: 12 pages, 10 figure

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