We present the first observation of the $\Omega_{ c}^{ 0} \to \Omega^{ -} \mu^{ +} \nu_{ \mu}$ decay and present measurements of the branching fraction ratios of the $\Omega_{ c}^{ 0} \to \Omega^{ -} \ell^{ +} \nu_{ \ell}$ decays compared to the reference mode $\Omega_{ c}^{ 0} \to \Omega^{ -} \pi^+$, ($\ell = e$ or $\mu$). This analysis is based on 89.5 fb$^{ -1}$, 711 fb$^{ -1}$, and 121.1 fb$^{ -1}$ data samples collected with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider at the center-of-mass energies of 10.52 GeV, 10.58 GeV, and 10.86 GeV, respectively. The $\Omega_{ c}^{ 0}$ signal yields are extracted by fitting $M_{ \Omega^{ -} \ell^{ +}}$ and $M_{ \Omega^{ -}\pi^+}$ spectra. The branching fraction ratios ${ \cal B}(\Omega_{ c}^{ 0} \to \Omega^{ -} e^{ +} \nu_{ e})/{ \cal B}(\Omega_{ c}^{ 0} \to \Omega^{ -} \pi^+)$ and ${ \cal B}(\Omega_{ c}^{ 0} \to \Omega^{ -} \mu^{ +} \nu_{ \mu})/{ \cal B}(\Omega_{ c}^{ 0} \to \Omega^{ -} \pi^+)$ are measured to be $1.98 \pm0.13~({ \rm stat.}) \pm 0.08~({ \rm syst.})$ and $ 1.94 \pm 0.18~({ \rm stat.}) \pm 0.10~({ \rm syst.})$, respectively. The ratio of ${ \cal B}(\Omega_{ c}^{ 0} \to \Omega^{ -} e^{ +} \nu_{ e})/{ \cal B}(\Omega_{ c}^{ 0} \to \Omega^{ -} \mu^{ +} \nu_{ \mu})$ is measured to be $1.02 \pm 0.10~({ \rm stat.}) \pm 0.02~({ \rm syst.})$, which is consistent with the expectation of lepton flavor universality.
Categories: hep-ex hep-ph