A resonance-like structure as narrow as 10 MeV is observed in the K−p invariant mass distributions in Λc+→pK−π+ at Belle. Based on the large data sample of about 1.5 million events and the small bin width of just 1 MeV for the K−p invariant mass spectrum, the narrow peak is found precisely lying at the Λη threshold. While lacking evidence for a quark model state with such a narrow width at this mass region, we find that this narrow structure can be naturally identified as a threshold cusp but enhanced by the nearby triangle singularity via the Λ-a0(980)+ or η-Σ(1660)+ rescatterings.
@article{arxiv.1906.07942,
title = {Visible narrow cusp structure in $\Lambda_c^+\to p K^- \pi^+$ enhanced by triangle singularity},
author = {Xiao-Hai Liu and Gang Li and Ju-Jun Xie and Qiang Zhao},
journal= {arXiv preprint arXiv:1906.07942},
year = {2019}
}