Measurement of the Matrix Element for the Decay ${\eta }^{\prime }\to \eta {\pi }^{+}{\pi }^{-}$

The BESIII Collaboration

The Dalitz plot of ${\eta }^{\prime }\to \eta {\pi }^{+}{\pi }^{-}$ decay is studied using $(225.2\pm 2.8)\times 10^6$ $\jpsi$ events collected with the BESIII detector at the BEPCII $e^{+}{e}^{-}$ collider. Wi…