We present the first measurements of the absolute branching fractions of $\Xi_c^+$ decays into $\Xi^- \pi^+ \pi^+$ and $p K^- \pi^+$ final states. Our analysis is based on a data set of $(772\pm 11)\times 10^{ 6}$ $B\bar{ B}$ pairs collected at the $\Upsilon(4S)$ resonance with the Belle detector at the KEKB $e^+e^-$ collider. We measure the absolute branching fraction of $\bar{ B}^{ 0} \to \bar{ \Lambda}_{ c}^{ -} \Xi_{ c}^{ +}$ with the $\Xi_c^+$ recoiling against $\bar{ \Lambda}_c^-$ in $\bar{ B}^0$ decays resulting in ${ \cal B}(\bar{ B}^{ 0} \to \bar{ \Lambda}_{ c}^{ -} \Xi_{ c}^{ +}) = [1.16 \pm 0.42(\rm stat.) \pm 0.15(\rm syst.)] \times 10^{ -3}$. We then measure the product branching fractions ${ \cal B}(\bar{ B}^{ 0} \to \bar{ \Lambda}_c^- \Xi_c^+){ \cal B}(\Xi_c^+ \to \Xi^- \pi^+ \pi^+)$ and ${ \cal B}(\bar{ B}^{ 0} \to \bar{ \Lambda}_c^- \Xi_c^+){ \cal B}(\Xi_c^+ \to p K^- \pi^+)$. Dividing these product branching fractions by $\bar{ B}^{ 0} \to \bar{ \Lambda}_{ c}^{ -} \Xi_{ c}^{ +}$ yields: ${ \cal B}(\Xi_c^+ \to \Xi^- \pi^+ \pi^+) = [2.86 \pm 1.21(\rm stat.) \pm 0.38(\rm syst.)]\%$ and ${ \cal B}(\Xi_c^+ \to p K^- \pi^+)=[0.45 \pm 0.21(\rm stat.) \pm 0.07(\rm syst.)]\%$. Our result for ${ \cal B}(\Xi_c^+ \to \Xi^- \pi^+ \pi^+)$ can be combined with $\Xi_c^+$ branching fractions measured relative to $\Xi_c^+ \to \Xi^- \pi^+ \pi^+$ to set the absolute scale for many $\Xi_c^+$ branching fractions.
Categories: hep-ex hep-ph