A search for a massless dark photon ${\gamma }^{\prime }$ is conducted using $4.5{\mathrm{fb}}^{-1}$ of $e^{+}{e}^{-}$ collision data collected at center-of-mass energies between 4.600 and 4.699 GeV with the BESIII detector at BEPCII. No significant signal is observed, and the upper limit on the branching fraction $\mathcal{B}({\mathrm{\Lambda }}_c^{+}\to p{\gamma }^{\prime })$ is determined to be $8.0\times {10}^{-5}$ at 90% confidence level.

• Received 9 August 2022
• Accepted 12 October 2022

DOI:https://doi.org/10.1103/PhysRevD.106.072008

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Published by the American Physical Society