Decay of the $\Lambda(1405)$ Hyperon to $\Sigma^0\pi^0$ Measured at GlueX

TL;DR

This paper reports the measurement of the decay line shape of the $ ext{Lambda}(1405)$ hyperon to $ ext{Sigma}^0 ext{pi}^0$ using GlueX data, providing insights into its structure and the nature of its two-pole hypothesis.

Contribution

It presents the first measurement of the $ ext{Lambda}(1405)$ decay to $ ext{Sigma}^0 ext{pi}^0$ at GlueX, analyzing the line shape and reaction dynamics in a new experimental context.

Findings

Preliminary $d\sigma/dM_{\Sigma^0\pi^0}$ results obtained.

Line shape analysis supports the two-pole hypothesis.

Data shows minimal contamination from other resonances.

Abstract

Among the light baryons, the $J^\pi = \frac{1}{2}^-$ $\Lambda(1405)$ hyperon is an important special case as it sits just below the $N\bar{K}$ threshold and decays almost exclusively to $\Sigma\pi$. Some long-standing hypotheses for $\Lambda(1405)$ are that it could be a $N\bar{K}$ bound state or a $\Sigma\pi$ continuum resonance. It may also be considered as a simple quark-model resonance, the $P$-wave companion of the $\Lambda(1520)$. In recent years chiral unitary models have suggested that there are two isospin zero poles present in this mass region, and that the "line shape" of the $\Lambda(1405)$ depends to what extent each of the two poles are stimulated in a given reaction. Below the $N\bar{K}$ threshold, the $\Lambda(1405)$ decays to the three $\Sigma\pi$ charge combinations. The $\Sigma^{0}\pi^{0}$ mode is purely $I=0$ and it is uncontaminated by complications arising from $I=1$ scattering processes contributing to the reaction mechanism in the $\Sigma^{+}\pi^{-}$ and $\Sigma^{-}\pi^{+}$ decays. It is also not affected from production and decay of the nearby $\Sigma^{0}(1385)$ hyperon. The GlueX experiment at Jefferson Lab has been used to study the $\Lambda(1405) \to \Sigma^{0}\pi^{0}$ decay mode. We focus on the preliminary results of $d\sigma/dM_{\Sigma^{0}\pi^{0}}$ and fits to the line shape of the $\Lambda(1405)$ region in the $-(t-t_{min})$ range 0 - 1.5 GeV$^2$ from analyzing the reaction $\gamma p \to K^{+}\Lambda^*$ using the data collected during the first phase of the GlueX program.