Studying triangle singularity through spin observables

Ke Wang, Shao-Fei Chen, Bo-Chao Liu

In this work, we study the spin density matrix element ${\rho }_{00}$ of the $\varphi$ in the decay $J/\psi \to \eta \pi \varphi$. In previous studies, a band around 1.4 GeV on the ${\pi }^0\varphi$ distribution…