Probing the isospin structure and low-lying resonances in $Λ_c^+ \to n\bar{K}^0 π^+$ decays

Abstract: The Cabibbo-favored decay $Λ_c⁺ \to n \bar{K}<sup>0π<sup>+$ offers a unique window to explore unresolved puzzles in the low-energy baryon spectroscopy and the isospin dynamics of the $\bar{K}N$ system. Recent experimental results present a, for now, contradiction: LHCb and Belle analyses of $Λ_c⁺ \to p K<sup>-π<sup>+$ suggest the $pK<sup>-$ ($I=0$) component dominates, while the BESIII hints at significant contributions from both isospin $0$ and $1$ in the $n\bar{K}<sup>0$ system of $Λ_c⁺ \to n K_S⁰ π<sup>+$. Furthermore, the measured branching fraction of $Λ_c⁺ \to n K_S⁰ π<sup>+$ exceeds SU(3) symmetry predictions by a factor of 3-4, signaling strong contributions from low-lying resonances. In this work, we provide a theoretical analysis of $Λ_c⁺ \to n \bar{K}<sup>0π<sup>+$ within the coupled-channel chiral unitary approach, where the $N(1535)$ and $Λ(1670)$ can be dynamically generated. Our calculations show a narrow peak from $N(1535)$ in the $π⁺ n$ invariant mass spectrum and a distinct dip from $Λ(1670)$ in the $\bar{K}⁰ n$ spectrum. The dip structure is qualitatively consistent with the $Λ(1670)$ manifestation in $\bar{K}N \to \bar{K}N$ scattering, supporting its molecular interpretation. This study not only connects the experimental observations but also highlights $Λ_c⁺ \to n \bar{K}<sup>0π<sup>+$ as a crucial process to disentangle the nature of $N(1535)$ and $Λ(1670)$. Future precise measurements of this decay channel by the BESIII, Belle II, LHCb, and the proposed Super Tau-Charm Factory are strongly encouraged.