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

TL;DR

This study searches for the rare decay of eta' into K pi and measures the branching fraction of J/psi to phi eta', finding no signal for the rare decay but confirming the known branching ratio of the latter.

Contribution

First search for eta' to K pi decay in J/psi events and precise measurement of J/psi to phi eta' branching fraction using a large data sample.

Findings

No significant eta' to K pi signal observed.

Upper limit set on eta' to K pi decay ratio.

Measured J/psi to phi eta' branching fraction consistent with previous results.

Abstract

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