A mechanism of baryogenesis and dark matter production via $B$ meson oscillations and decays has recently been proposed to explain the observed dark matter abundance and matter-antimatter asymmetry in the universe. This mechanism introduces a low-mass dark sector particle (${\psi }_D$) with a nonzero baryonic charge. We present a search for this new state in $B^{+}\to {\mathrm{\Lambda }}_c^{+}{\psi }_D$ decays using data collected at the $\mathrm{\Upsilon }(4S)$ resonance by the BABAR detector at SLAC, corresponding to an integrated luminosity of $431.0{\mathrm{fb}}^{-1}$. The search leverages the full reconstruction of the $B^{-}$ meson in $\mathrm{\Upsilon }(4S)\to B^{+}{B}^{-}$ decays, accompanied by the reconstruction of a ${\mathrm{\Lambda }}_c^{+}$, to infer the presence of ${\psi }_D$. No significant signal is observed, and limits on the $B^{+}\to {\mathrm{\Lambda }}_c^{+}{\psi }_D$ branching fraction are set at the level of $1.6\times {10}^{-4}$ at 90% confidence level for $0.94<m_{{\psi }_D}<2.99\mathrm{GeV}$. These results set strong constraints on the parameter space allowed by $B$-meson baryogenesis.

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• Baryogenesis & leptogenesis
• Particle dark matter