We present a search for seven lepton-flavor-violating neutral charm meson decays of the type $D^0\to X^0{e}^{\pm }{\mu }^{\mp }$, where $X^0$ represents a ${\pi }^0$, $K_{\mathit{S}}^0$, ${\overline{K}}^{*0}$, ${\rho }^0$, $\varphi$, $\omega$, or $\eta$ meson. The analysis is based on $468{\mathrm{fb}}^{-1}$ of $e^{+}{e}^{-}$ annihilation data collected at or close to the $\mathrm{\Upsilon }(4S)$ resonance with the BABAR detector at the SLAC National Accelerator Laboratory. No significant signals are observed, and we establish 90% confidence level upper limits on the branching fractions in the range $(5.0-22.5)\times {10}^{-7}$. The limits are between 1 and 2 orders of magnitude more stringent than previous measurements.

• Received 21 April 2020
• Accepted 26 May 2020

DOI:https://doi.org/10.1103/PhysRevD.101.112003

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Published by the American Physical Society