Using the entire data sample of $980$ $fb^{ -1}$ integrated luminosity collected with the Belle detector at the KEKB asymmetric-energy $e^{ +}e^{ -}$ collider, we present an amplitude analysis measuring the branching fractions of the Cabibbo-allowed, $W$-exchange resonant decay $\Xi_{ c}^{ 0} \rightarrow \Xi^{ 0} \phi (\to K^+ K^-)$ with a polarized $\phi$ and the non-resonant decay via a direct process $\Xi_{ c}^{ 0} \rightarrow \Xi^{ 0} K^+ K^-$. We present these measurements, relative to the normalization mode $\Xi^{ -}\pi^{ +}$, and find branching ratios $\frac{ \mathcal{ B}(\Xi_{ c}^{ 0} \rightarrow \Xi^{ 0} \phi (\rightarrow K^{ +}K^{ -}))}{ \mathcal{ B}(\Xi_{ c}^{ 0} \rightarrow \Xi^{ -} \pi^{ +})} = 0.036 \pm 0.004 (stat.) \pm 0.002 (syst.)$ and $\frac{ \mathcal{ B}(\Xi_{ c}^{ 0} \rightarrow \Xi^{ 0} K^{ +} K^{ -})}{ \mathcal{ B}(\Xi_{ c}^{ 0} \rightarrow \Xi^{ -} \pi^{ +})} = 0.039 \pm 0.004 (stat.) \pm 0.002 (syst.)$ which suggest that only minor cusping peaks occur in the combinatorial background of $\Omega^{ *-} \to \Xi^{ 0}K^{ -}$ due to these $\Xi_{ c}^{ 0}$ decays.
Categories: hep-ex