Precision Measurement of the Branching Fractions of ${\eta }^{\prime }$ Decays

Based on a sample of $\left(1310.6±7.0\right)×{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 $J/\psi \to \gamma {\eta }^{\prime }$. By analyzing events where the radiative photon converts into an ${e}^{+}{e}^{-}$ pair, the branching fraction for $J/\psi \to \gamma {\eta }^{\prime }$ is measured to be $\left(5.27±0.03±0.05\right)×{10}^{-3}$. The absolute branching fractions of the five dominant decay channels of the ${\eta }^{\prime }$ are then measured for the first time and are determined to be $B\left({\eta }^{\prime }\to \gamma {\pi }^{+}{\pi }^{-}\right)=\left(29.90±0.03±0.55\right)%$, $B\left({\eta }^{\prime }\to \eta {\pi }^{+}{\pi }^{-}\right)=\left(41.24±0.08±1.24\right)%$, $B\left({\eta }^{\prime }\to \eta {\pi }^{0}{\pi }^{0}\right)=\left(21.36±0.10±0.92\right)%$, $B\left({\eta }^{\prime }\to \gamma \omega \right)=\phantom{\rule{0ex}{0ex}}\left(2.489±0.018±0.074\right)%$, and $B\left({\eta }^{\prime }\to \gamma \gamma \right)=\left(2.331±0.012±0.035\right)%$, where the first uncertainties are statistical and the second systematic.