We report branching fraction measurements of four decay modes of the $\Lambda_{ c}^{ +}$ baryon, each of which includes an $\eta$ meson and a $\Lambda$ baryon in the final state, and all of which are measured relative to the $\Lambda_{ c}^{ +} \rightarrow p K^{ -} pi^{ +}$ decay mode. The results are based on a $980~\mathrm{ fb^{ -1}}$ data sample collected by the Belle detector at the KEKB asymmetric-energy $e^{ +}e^{ -}$ collider. Two decays, $\eta \Sigma^{ 0} \pi^{ +}$ and $\Lambda(1670) \pi^{ +}$, are observed for the first time, while the measurements of the other decay modes, $\Lambda_{ c}^{ +} \rightarrow \eta\Lambda\pi^{ +}$ and $\eta\Sigma(1385)^{ +}$, are more precise than those made previously. We obtain $\mathcal{ B}(\Lambda_{ c}^{ +} \rightarrow \eta \Lambda \pi^{ +})/\mathcal{ B}(\Lambda_{ c}^{ +} \rightarrow p K^{ -} \pi^{ +})$ = $0.293 \pm 0.003 \pm 0.014$, $\mathcal{ B}(\Lambda_{ c}^{ +} \rightarrow \eta \Sigma^{ 0} \pi^{ +})/\mathcal{ B}(\Lambda_{ c}^{ +} \rightarrow p K^{ -} \pi^{ +})$ = $0.120 \pm 0.006 \pm 0.006$, $\mathcal{ B}(\Lambda_{ c}^{ +} \rightarrow \Lambda(1670) \pi^{ +}) \times \mathcal{ B}(\Lambda(1670) \rightarrow \eta \Lambda)/\mathcal{ B}(\Lambda_{ c}^{ +} \rightarrow p K^{ -} \pi^{ +})$ = $(5.54 \pm 0.29 \pm 0.73 ) \times 10^{ -2}$, and $\mathcal{ B}(\Lambda_{ c}^{ +} \rightarrow \eta \Sigma(1385)^{ +})/\mathcal{ B}(\Lambda_{ c}^{ +} \rightarrow p K^{ -} \pi^{ +})$ = $0.192 \pm 0.006 \pm 0.016$. The mass and width of the $\Lambda(1670)$ are also precisely determined to be $1674.3 \pm 0.8 \pm 4.9~{ \rm MeV}/c^{ 2}$ and $36.1 \pm 2.4 \pm 4.8~{ \rm MeV}$, respectively, where the uncertainties are statistical and systematic, respectively.
Categories: hep-ex