Could an axion-like particle be hidden in ${\eta }_c\to \gamma \gamma$?

Zhi-Jun Li, Zheng-Yun You, Xiao-Rui Lyu

We discuss the possibility of an axion-like particle being merged in the recent observation of ${\eta }_c\to \gamma \gamma$ at BESIII and find that it cannot be excluded in the current experimenta…