Role of the possible $\Sigma^*(\frac{1}{2}^-)$ state in the $\Lambda p \to \Lambda p \pi^0$ reaction

TL;DR

This study investigates the role of a hypothesized $rac{1}{2}^-$ $ ext{Sigma}^*$ state in the $ ext{Lambda} p o ext{Lambda} p ext{pi}^0$ reaction near threshold, showing that including this state improves agreement with experimental data.

Contribution

The paper introduces and tests the impact of a new $rac{1}{2}^-$ $ ext{Sigma}^*$ resonance in modeling the reaction, which enhances the fit to experimental results.

Findings

Including the $rac{1}{2}^-$ $ ext{Sigma}^*$ state improves data description.

Single-pion exchange dominates the reaction process.

Angular distributions can reveal the presence of the $rac{1}{2}^-$ state.

Abstract

The $\Lambda p \to \Lambda p \pi^0$ reaction near threshold is studied within an effective Lagrangian method. The production process is described by single-pion and single-kaon exchange. In addition to the role played by the $\Sigma^*(1385)$ resonance of spin-parity $J^P = 3/2^+$, the effects of a newly proposed $\Sigma^*$ ($J^P = 1/2^-$) state with mass and width around $1380$ MeV and $120$ MeV are investigated. We show that our model leads to a good description of the experimental data on the total cross section of the $\Lambda p \to \Lambda p \pi^0$ reaction by including the contributions from the possible $\Sigma^*(\frac{1}{2}^-)$ state. However, the theoretical calculations by considering only the $\Sigma^*(1385)$ resonance fail to reproduce the experimental data, especially for the enhancement close to the reaction threshold. On the other hand, it is found that the single-pion exchange is dominant. Furthermore, we also demonstrate that the angular distributions provide direct information of this reaction, hence could be useful for the investigation of the existence of the $\Sigma^*(\frac{1}{2}^-)$ state and may be tested by future experiments.