# Observation of $\psi(3686) \to p \bar{p} \eta^{\prime}$ and improved measurement of $J/\psi \to p \bar{p} \eta^{\prime}$

## TL;DR

This paper reports the first observation of the decay process $(3686)  p ar{p} ta^{}$ with high significance and provides improved measurements of the branching fractions for $J//(3686)$ decays, along with the $ta-ta^{}$ mixing angle.

## Contribution

First observation of $(3686)  p ar{p} ta^{}$ decay and improved measurement of $J/$ decay branching fractions, including determination of the $ta-ta^{}$ mixing angle.

## Key findings

- Branching fraction $B((3686)  p ar{p} ta^{}) = (1.10 \u00b1 0.10  0.08) imes 10^{-5}$
- Branching fraction $B(J/  p ar{p} ta^{}) = (1.26 \u00b1 0.02  0.07) imes 10^{-4}$
- Determined $ta-ta^{}$ mixing angles of approximately $-24^\u00b0$ with uncertainties.

## Abstract

We observe the process $\psi(3686) \to p \bar{p} \eta^{\prime}$ for the first time, with a statistical significance higher than 10$\sigma$, and measure the branching fraction of $J/\psi \to p \bar{p} \eta^{\prime}$ with an improved accuracy compared to earlier studies. The measurements are based on $4.48 \times 10^8$ $\psi(3686)$ and $1.31 \times 10^{9}$ $J/\psi$ events collected by the BESIII detector operating at the BEPCII. The branching fractions are determined to be $B(\psi(3686) \to p \bar{p} \eta^{\prime}) = (1.10\pm0.10\pm0.08)\times10^{-5}$ and $B(J/\psi \to p \bar{p} \eta^{\prime})=(1.26\pm0.02\pm 0.07)\times10^{-4}$, where the first uncertainties are statistical and the second ones systematic. Additionally, the $\eta-\eta^{\prime}$ mixing angle is determined to be $-24^{\circ} \pm 11^{\circ}$ based on $\psi(3686) \to p \bar{p} \eta^{\prime}$, and $-24^{\circ} \pm 9^{\circ}$ based on $J/\psi \to p \bar{p} \eta^{\prime}$, respectively.