Search for the Σ(1380)1/2− state in Λc+

Abstract

In this work, we investigate the resonance production in Λc+→γπ+Λ decay through the triangle singularity (TS) mechanism, within an effective Lagrangian approach. We find that the appropriate loop decay process could develop a triangle singularity in the invariant mass MπΛ around 1.35 GeV, with the shape depending on the quantum numbers of Σ* states that couple to the final πΛ system. Especially, the Σ(1380)1/2− state newly predicted in the pentaquark model, if exists, significantly enhances the TS contribution and sharpens the TS peak due to the S-wave Σ*πΣ vertex in the loop. Therefore, the existence of the Σ(1380)1/2− state can be examined by measuring the TS signal in Λc+→γπ+Λ. Considering also possible tree-level diagrams, we additionally obtain the branching ratio Br(Λc+→γπ+Λ)≃1.5×10−5. We suggest the investigation of this reaction by future BESIII, LHCb, and Belle experiments. Published by the American Physical Society 2024