Two-pion emission decays of negative parity singly heavy baryons

Abstract

We investigate two-pion emission decays of singly charmed and bottom baryons, focusing on $Λ_Q^*(1P)$ and $Ξ_Q^*(1P)$ with $Q=c$ (charm) or $b$ (bottom) quarks and $J^P=1/2^-,3/2^-$, belonging to antisymmetric flavor triplet $\bar{\boldsymbol{3}}_F$. Our analysis encompasses both sequential processes, involving intermediate states belonging to symmetric flavor sextet $\boldsymbol{6}_F$ such as $Σ_Q(1S)$ and $Ξ_Q^\prime(1S)$ respectively with $J^P=1/2^+,3/2^+$, derived from the chiral quark model, and direct process crucial for comparison with experimental data, whose coupling constants estimated using the chiral-partner scheme. We also incorporate the convolution of the parent particle's mass for the Dalitz plot, enabling a more realistic comparison with experimental data. We scrutinize the Dalitz plots of these negative parity states in light of recent Belle measurements for $Λ_c(2625)^+$. Our findings support the assignment of $Λ_c(2625)^+$ as the $λ$-mode excitation with $J^P=3/2^-$ in the quark model, deduced from the the ${Λ_cπ}$ invariant mass distribution, and we then give predictions for other cases, including the $Ξ_Q^*$ decays. The observed asymmetry in the ${ππ}$ invariant mass distribution underscores the important role of the direct process, reflecting the chiral-partner structure in the heavy baryon sector. It is evident that the presence of the direct process is not significant in the three-body decays unless the $S$-wave resonance contribution is suppressed. We suggest further experimental verification to test our predictions and get more insights into the structure of heavy baryons.