Why $\Xi(1690)$ and $\Xi(2120)$ are so narrow?

TL;DR

This paper explains the narrow widths of certain $\\Xi$ baryons, like $\\Xi(1690)$ and $\\Xi(2120)$, through coupled channel meson-baryon dynamics using chiral and hidden local symmetry models.

Contribution

It provides a theoretical explanation for the narrow widths of specific $\\Xi$ baryons based on hadron dynamics, matching experimental data.

Findings

The narrow width of $\\Xi(1690)$ is explained by coupled channel dynamics.

A new narrow resonance related to $\\Xi(2120)$ is identified.

No exotic $\\Xi^{+}$ or $\\Xi^{--}$ states are found.

Abstract

The $\Xi$ baryons are expected to be naturally narrower as compared to their nonstrange and strange counterparts since they have only one light quark and, thus, their decay involves producing either a light meson and doubly strange baryon or both meson and baryon with strangeness which involves, relatively, more energy. In fact, some $\Xi$'s have full widths of the order of even 10-20 MeV when, in principle, they have a large phase space to decay to some open channels. Such is the case of $\Xi (1690)$, for which the width has been found to be of the order of 10 MeV in the latest {\it BABAR} and BELLE data. In this manuscript we study why some $\Xi$'s are so narrow. Based on a coupled channel calculation of the pseudoscalar meson-baryon and vector meson-baryon systems with chiral and hidden local symmetry Lagrangians, we find that the answer lies in the intricate hadron dynamics. We find that the known mass, width, spin-parity and branching ratios of $\Xi (1690)$ can be naturally explained in terms of coupled channel meson-baryon dynamics. We find another narrow resonance which can be related to $\Xi(2120)$. We also look for exotic states $\Xi^{+}$ and $\Xi^{--}$ but find none. In addition we provide the cross sections for $ \bar K \Lambda, \bar K \Sigma \rightarrow \pi \Xi$ which can be useful for understanding the enhanced yield of $\Xi$ reported in recent studies of heavy ion collisions.