Search for Rare $b$ to Open-Charm Two-Body Decays of Baryons at LHCb

A search for the rare two-body decays $\Lambda_b\rightarrow D^0 \Lambda$ and $\Xi^0_b\rightarrow D^0 \Lambda$ is performed with proton-proton collision data, corresponding to an integrated luminosity of 6$fb^{-1}$, collected by the LHCb experiment at a center-of-mass energy of 13 TeV. The decay $\Lambda_b\rightarrow D^0 \Lambda$ is seen with a statistical significance of 5.5 standard deviations, and constitutes the discovery for this decay. The branching fraction, measured using the $\Lambda_b\rightarrow D^0p\pi^-$ decay for normalization, is \begin{equation*} B(\Lambda_b\rightarrow D^0 \Lambda) = (9.9 \pm 2.3 \pm 1.6 \pm 1.1) \times 10^{-6} \,, \end{equation*} where the uncertainties are statistical, systematic, and external, respectively. An excess of $\Xi^0_b\rightarrow D^0 \Lambda$ candidates w.r.t. the background is observed with a statistical significance of 1.8 standard deviations and is used to estimate the upper limit \begin{equation*} \frac{f_{\Xi^0_b}}{f_{\Lambda_b}} \times \frac{B{(\Xi^0_c \rightarrow D^0\Lambda)}}{B{(\Lambda_b\rightarrow D^0\Lambda})} < 0.5 \quad (\text{CL}\,=\,95\,\%) \,, \end{equation*} where $f_{\Xi^0_b} / f_{\Lambda^b}$ is the ratio of the fragmentation fractions of $b$-quarks into $\Xi^0_b$ and $\Lambda_b$ baryons.