Measurements of branching ratios for η decays into charged particles

The WASA-at-COSY experiment has collected $3\ifmmode\times\else\texttimes\fi{}{10}^{7}$ events with $\ensuremath{\eta}$ mesons produced via the reaction $pd\ensuremath{\rightarrow}^{3}\mathrm{He}\phantom{\rule{0.16em}{0ex}}\ensuremath{\eta}$ at $\mathrm{T}=1.0\phantom{\rule{4pt}{0ex}}\mathrm{GeV}$. Using this data set, we evaluate the branching ratios of the decays $\ensuremath{\eta}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}\ensuremath{\gamma}$, $\ensuremath{\eta}\ensuremath{\rightarrow}{e}^{+}{e}^{\ensuremath{-}}\ensuremath{\gamma}$, $\ensuremath{\eta}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}{e}^{+}{e}^{\ensuremath{-}}$, and $\ensuremath{\eta}\ensuremath{\rightarrow}{e}^{+}{e}^{\ensuremath{-}}{e}^{+}{e}^{\ensuremath{-}}$. The branching ratios are normalized to the $\ensuremath{\eta}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\pi}}^{0}$ decay. In addition an upper limit on a $CP$-violating asymmetry in $\ensuremath{\eta}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}{e}^{+}{e}^{\ensuremath{-}}$ is extracted.