Observation ofη′→π+π−π+π−andη′→π+π−π0π0

Using a sample of $1.3\ifmmode\times\else\texttimes\fi{}{10}^{9}\text{ }\text{ }J/\ensuremath{\psi}$ events collected with the BESIII detector, we report the first observation of ${\ensuremath{\eta}}^{\ensuremath{'}}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$ and ${\ensuremath{\eta}}^{\ensuremath{'}}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\pi}}^{0}{\ensuremath{\pi}}^{0}$. The measured branching fractions are $\mathcal{B}({\ensuremath{\eta}}^{\ensuremath{'}}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}})=[8.53\ifmmode\pm\else\textpm\fi{}0.69(\text{stat.})\ifmmode\pm\else\textpm\fi{}0.64(\text{syst.})]\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}$ and $\mathcal{B}({\ensuremath{\eta}}^{\ensuremath{'}}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\pi}}^{0}{\ensuremath{\pi}}^{0})=[1.82\ifmmode\pm\else\textpm\fi{}0.35(\text{stat.})\ifmmode\pm\else\textpm\fi{}\phantom{\rule{0ex}{0ex}}0.18(\text{syst.})]\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$, which are consistent with theoretical predictions based on a combination of chiral perturbation theory and vector-meson dominance.