Search for the weak decay $eta^{prime}to K^{pm}pi^{mp}$ and precise measurement of the branching fraction ${cal B}(J/psitophieta^{prime})$

We present the first search for the rare decay of $eta^prime$ into $K^{pm}pi^{mp}$ in $J/psitophieta^{prime}$, using a sample of $1.3times10^{9}$ $J/psi$ events collected with the BESIII detector. No significant signal is observed, and the upper limit at the 90% confidence level for the ratio $frac{{cal B}(eta^{prime}to K^{pm}pi^{mp})}{{cal B}(eta^{prime}togammapi^{+}pi^{-})}$ is determined to be $1.3times10^{-4}$. In addition, we report the measurement of the branching fraction of $J/psitophieta^{prime}$ to be $(5.10pm0.03(text{stat.})pm0.32(text{syst.}))times10^{-4}$, which agrees with previous results from BESII.