# Precision measurement of the branching fractions of $\eta^\prime$ decays

## TL;DR

This paper reports precise measurements of the absolute branching fractions of the $ ext{J/} ext{psi}$ and $ ext{eta}^ ext{' }$ decays, providing the first independent determinations of the $ ext{eta}^ ext{' }$ decay channels using a large data sample from BESIII.

## Contribution

First independent measurements of the $ ext{eta}^ ext{' }$ decay branching fractions using $J/ ext{psi}$ radiative decays with conversion photon analysis.

## Key findings

- Measured $ ext{J/} ext{psi}
ightarrow ext{gamma} ext{eta}^ ext{' }$ branching fraction as $(5.27 extpm0.03 extpm0.05) imes 10^{-3}$.
- Determined five dominant $ ext{eta}^ ext{' }$ decay branching fractions with high precision.
- Provided new data for $ ext{eta}^ ext{' }$ decay channels for theoretical and experimental studies.

## Abstract

Based on a sample of $(1310.6 \pm 7.0) \times 10^6~J/\psi$ events collected with the BESIII detector, we present measurements of $J/\psi$ and $\eta^\prime$ absolute branching fractions using the process $J/\psi\rightarrow\gamma\eta^\prime$. By analyzing events where the radiative photon converts into an $e^+e^-$ pair, the branching fraction for $J/\psi \rightarrow \gamma \eta^\prime$ is measured to be $(5.27\pm0.03\pm0.05)\times 10^{-3}$. The absolute branching fractions of the five dominant decay channels of the $\eta^\prime$ are then measured independently for the first time and are determined to be $\mathcal{B}(\eta^\prime \rightarrow \gamma \pi^{+} \pi^{-})$ = (29.90$\pm$0.03$\pm$0.55)%, $\mathcal{B}(\eta^\prime \rightarrow \eta \pi^{+} \pi^{-})$ = (41.24$\pm$0.08$\pm$1.24)%, $\mathcal{B}(\eta^\prime \rightarrow \eta \pi^{0} \pi^{0})$ = (21.36$\pm$0.10$\pm$0.92)%, $\mathcal{B}(\eta^\prime \rightarrow \gamma \omega)$ = (2.489$\pm$0.018$\pm$0.074)%, and $\mathcal{B}(\eta^\prime \rightarrow \gamma \gamma)$ = (2.331$\pm$0.012$\pm$0.035)%, where the first uncertainties are statistical and the second systematic.