The role of triangle singularity in isospin breaking process $J/\psi \to \Lambda \bar{\Lambda} \pi$ and the possible evidence of $\Sigma^*(\frac{1}{2}^-)$ states

TL;DR

This paper explores how triangle singularities influence the isospin-breaking decay of J/psi into Lambda, anti-Lambda, and pion, suggesting they cause resonance-like features and proposing experimental searches for elusive Sigma* states.

Contribution

It demonstrates the significant role of triangle singularities in J/psi decay processes and predicts resonance structures linked to Sigma* states around 1.4 GeV and 1.6 GeV.

Findings

Triangle singularity causes a resonance-like structure near 1.4 GeV.

Two Sigma*(1/2^-) states are essential for amplifying the singularity effect.

Experimental suggestions for BESIII and STCF to verify the predictions.

Abstract

In this study, the impact of triangle singularity is investigated in the isospin-breaking process $J/\psi \to \Lambda \bar{\Lambda} \pi$. The triangle singularity is found to play a significant role in the process, resulting in the creation of a resonance-like structure around 1.4 GeV in the $\Lambda\pi(\bar{\Lambda}\pi)$ invariant mass spectrum. To amplify the impact of this triangle singularity, the presence of two $\Sigma^*(\frac{1}{2}^-)$ states around 1.4 GeV and 1.6 GeV is essential, yet these states have not been definitively identified in the current baryon spectrum. We recommend that experiments, particularly the Beijing Spectrometer (BESIII) and the future Super Tau-Charm Factory (STCF), to investigate the process $J/\psi \to \Lambda \bar{\Lambda} \pi$ to offer direct evidences for our predicted triangle singularity and additional evidence regarding the $\Sigma(\frac{1}{2}^-)$ states.