Search for the $Σ^*$ state in $Λ^+_c \to π^+ π^0 π^-Σ^+$ decay by triangle singularity

Abstract

A $Σ^*$ resonance with spin-parity $J^P = 1/2^-$ and mass in the vicinity of the $\bar{K}N$ threshold has been predicted in the unitary chiral approach and inferred from the analysis of CLAS data on the $γp \to K^+ π^0 Σ^0$ reaction. In this work, based on the dominant Cabibbo favored weak decay mechanism, we perform a study of $Λ_c^+ \to π^+ π^0 Σ^*$ with the possible $Σ^*$ state decaying into $π^- Σ^+$ through a triangle diagram. This process is initiated by $ Λ_c^+ \to π^+ \bar{K}^*N $, then the $\bar{K}^*$ decays into $\bar{K} π$ and $\bar{K} N$ produce the $Σ^*$ through a triangle loop containing $\bar{K}^* N \bar{K}$ which develops a triangle singularity. We show that the $π^- Σ^+$ state is generated from final state interaction of $\bar{K}N$ in $S$-wave and isospin $I=1$, and the $Λ_c^+ \to π^+ π^0 π^- Σ^+$ decay can be used to study the possible $Σ^*$ state around the $\bar{K}N$ threshold. The proposed decay mechanism can provide valuable information on the nature of the $Σ^*$ resonance and can in principle be tested by facilities such as LHCb, BelleII and BESIII.