A new dark sector antibaryon, denoted ${\psi }_{\mathrm{D}}$, could be produced in decays of $B$ mesons. This Letter presents a search for $B^{+}\to {\psi }_{\mathrm{D}}+\mathrm{p}$ (and the charge conjugate) decays in $e^{+}{e}^{-}$ annihilations at 10.58 GeV, using data collected in the BABAR experiment. Data corresponding to an integrated luminosity of $398{\mathrm{fb}}^{-1}$ are analyzed. No evidence for a signal is observed. Branching fraction upper limits in the range from ${10}^{-7}–{10}^{-5}$ are obtained at 90% confidence level for masses of $1.0<m_{{\psi }_{\mathrm{D}}}<4.3\mathrm{GeV}/{\mathrm{c}}^2$. The result is also reinterpreted to provide the first limits on a supersymmetric model with $R$-parity violation and a light neutralino.

• Received 19 June 2023
• Accepted 12 October 2023

DOI:https://doi.org/10.1103/PhysRevLett.131.201801

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Published by the American Physical Society