First Evidence for an Unambiguous Triangle Singularity from $\psi (2S)\to p\bar{p}\eta$

Qi Huang, Yi-Jia Zeng, Xiao-Rui Lyu +2

Triangle singularities, predicted by Landau in 1959, are purely kinematic enhancements arising from hadronic rescattering loops. Despite their proposed role in various anomalous de…