Search for the doubly heavy baryons \begin{document}${\boldsymbol \varOmega_{\boldsymbol{bc}}^{\bf 0}} $\end{document} and \begin{document}$ {\boldsymbol\varXi_{\boldsymbol{bc}}^{\bf 0} }$\end{document} decaying to \begin{document}${ \boldsymbol \varLambda_c^+\pi^- }$\end{document} and \begin{document}$ {\boldsymbol\varXi_c^+\pi^- }$\end{document}

The first search for the doubly heavy \begin{document}$ {{{{\varOmega}_{bc}^{0}}}} $\end{document} baryon and a search for the \begin{document}$ {{{{\varXi}_{bc}^{0}}}} $\end{document} baryon are performed using \begin{document}$ pp $\end{document} collision data collected via the \begin{document}$ {\rm{LHCb}} $\end{document} experiment from 2016 to 2018 at a centre-of-mass energy of \begin{document}$ 13 \;{\rm{TeV}} $\end{document} , corresponding to an integrated luminosity of 5.2 \begin{document}$ \;{\rm{f}}{{\rm{b}}^{ - 1}} $\end{document} . The baryons are reconstructed via their decays to \begin{document}$ {{{{\varLambda}^+_c}}} {{{{\pi}^-}}} $\end{document} and \begin{document}$ {{{{\varXi}^+_c}}} {{{{\pi}^-}}} $\end{document} . No significant excess is found for invariant masses between 6700 and 7300 \begin{document}$ \;{\rm{MeV}}/{c^2} $\end{document} , in a rapidity range from 2.0 to 4.5 and a transverse momentum range from 2 to 20 \begin{document}$ \;{\rm{MeV}}/{c} $\end{document} . Upper limits are set on the ratio of the \begin{document}$ {{{{\varOmega}_{bc}^{0}}}} $\end{document} and \begin{document}$ {{{{\varXi}_{bc}^{0}}}} $\end{document} production cross-section times the branching fraction to \begin{document}$ {{{{\varLambda}^+_c}}}{{{{\pi}^-}}} $\end{document} ( \begin{document}$ {{{{\varXi}^+_c}}}{{{{\pi}^-}}} $\end{document} ) relative to that of the \begin{document}$ {{{{\varLambda}^0_b}}} $\end{document} ( \begin{document}$ {{{{\varXi}_{b}^{0}}}} $\end{document} ) baryon, for different lifetime hypotheses, at 95% confidence level. The upper limits range from \begin{document}$ 0.5\times10^{-4} $\end{document} to \begin{document}$ 2.5\times10^{-4} $\end{document} for the \begin{document}$ {{{{{{{{\varOmega}_{bc}^{0}}}}{{\rightarrow }}{{{{\varLambda}^+_c}}}{{{{\pi}^-}}}}}}} $\end{document} ( \begin{document}$ {{{{{{{{\varXi}_{bc}^{0}}}}{{\rightarrow }}{{{{\varLambda}^+_c}}}{{{{\pi}^-}}}}}}} $\end{document} ) decay, and from \begin{document}$ 1.4\times10^{-3} $\end{document} to \begin{document}$ 6.9\times10^{-3} $\end{document} for the \begin{document}$ {{{{{{{{\varOmega}_{bc}^{0}}}}{{\rightarrow }}{{{{\varXi}^+_c}}}{{{{\pi}^-}}}}}}} $\end{document} ( \begin{document}$ {{{{{{{{\varXi}_{bc}^{0}}}}{{\rightarrow }}{{{{\varXi}^+_c}}}{{{{\pi}^-}}}}}}} $\end{document} ) decay, depending on the considered mass and lifetime of the \begin{document}$ {{{{\varOmega}_{bc}^{0}}}} $\end{document} ( \begin{document}$ {{{{\varXi}_{bc}^{0}}}} $\end{document} ) baryon.