Observation of Ξb0→ Ξc + Ds- and Ξb0 c D- s decays

The $\Xibz \to \Xicp \Dsm$ and $\Xibm \to \Xicz \Dsm$ decays are observed for the first time using proton-proton collision data collected by the LHCb experiment at a centre-of-mass energy of $\sqs=13\tev$, corresponding to an integrated luminosity of $5.1\invfb$. The relative branching fractions times the beauty-baryon production cross-sections are measured to be \begin{align*} \mathcal{R}\left(\frac{\Xibz}{\Lb}\right) &\equiv \frac{\sigma\left(\Xibz\right)}{\sigma\left(\Lb\right)} \times \frac{\BF\left(\Xibz \to \Xicp \Dsm\right)}{\BF\left(\Lb \to \Lc \Dsm\right)} =(15.8\pm1.1\pm0.6\pm7.7)\%,\\ \mathcal{R}\left(\frac{\Xibm}{\Lb}\right) &\equiv \frac{\sigma\left(\Xibm\right)}{\sigma\left(\Lb\right)} \times \frac{\BF\left(\Xibm \to \Xicz \Dsm\right)}{\BF\left(\Lb \to \Lc \Dsm\right)} =(16.9\pm1.3\pm0.9\pm4.3)\%, \end{align*} where the first uncertainties are statistical, the second systematic, and the third due to the uncertainties on the branching fractions of relevant charm-baryon decays. The masses of \Xibz and \Xibm baryons are measured to be \mbox{$m_{\Xibz}=5791.12\pm0.60\pm0.45\pm0.24\mevcc$} and \mbox{$m_{\Xibm}=5797.02\pm0.63\pm0.49\pm0.29\mevcc$}, where the uncertainties are statistical, systematic, and those due to charm-hadron masses, respectively.