$\Lambda_s (1405)$ and Negative Parity Baryon States

TL;DR

This paper reviews the nature of the $ar{ ext{K}}$ (1405) baryon, debating whether it is a three-quark state or a hadronic molecule, and discusses its implications in hadron structure and effective theories.

Contribution

It offers a comprehensive re-examination of the $ar{ ext{K}}$ (1405) controversy, proposing it as a state describable both as a quark model state and a hadronic bound state.

Findings

Empirical evidence suggests minimal mixing among negative parity baryon singlets and octets.

The $ar{ ext{K}}$ (1405) may be a dynamically generated state from inelastic channels.

The state can be interpreted as both a three-quark baryon and a hadronic molecule.

Abstract

After a brief historical background on the $\Ls$, we revisit the 25 year old controversy on whether $\Ls$ is a $qqq$ (L=1) three quark state or a $\K$ quasi virtual bound state. This work is stimulated by the recent suggestion of Isgur that s be treated as a heavy quark in heavy quark effective theory HQET. We re-examine the empirical evidence for minimal mixing amongst singlets and octets in negative parity baryon states, with a possible dynamical origin in the opening of inelastic threshold channels. Finally, we suggest that $\Ls$ belongs to a class of hadrons which are described simultaneously as $qqq$ or $q \bar{q}$ states and as hadronic bound states.