The role of triangle mechanism in the decay process $J/\psi \to K^- K^+ a_1(1260)$ is probed. In this mechanism, a close-up resonance with mass $1823$ MeV and width $122$ decays into $K^* \phi, K^* K \pi$ then \bar{K}$ fuses $a_1(1260)$ resonance. We find that leads to singularity around $M_{\rm inv}(K^- a_1(1260))\approx 1920$ MeV, where axial-vector meson considered as dynamically generated W...
