Search for the weak decay $η^{\prime}\to K^{\pm}π^{\mp}$ and precise measurement of the branching fraction ${\cal B}(J/ψ\toϕη^{\prime})$

Abstract

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