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arXiv · 2608.29159

Sensitivity of a Missing-Mass Search for a Light Dark Photon with a Positron Beam on a Hydrogen Target

Weizhi Xiong·Ashot Gasparian·Bogdan Wojtsekhowski
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Abstract

We present a Geant4-based simulation study of the sensitivity to a light dark photon, $A'$, using a positron beam incident on a thin liquid-hydrogen target and a high-resolution forward electromagnetic calorimeter for final-state photon reconstruction. This study is motivated by ongoing research and development toward a low-energy positron facility at Jefferson Lab. The proposed search employs the missing-mass technique in the annihilation-in-flight process $e^+e^- \to \gamma A'$, providing sensitivity to the $A'$ independently of its decay mode. We evaluate the expected backgrounds from standard QED annihilation and bremsstrahlung processes and present the projected sensitivity to the kinetic-mixing parameter $\epsilon^2$ as a function of the $A'$ mass. The experiment with 500~MeV beam will provide the data for $A'$ mass range 7-19 MeV. The projected sensitivity on $\epsilon^2$ is $4\times10^{-8}$ at $m_{A'}=19$~MeV.

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Weizhi Xiong, Ashot Gasparian, Bogdan Wojtsekhowski. 2026-08-29. Sensitivity of a Missing-Mass Search for a Light Dark Photon with a Positron Beam on a Hydrogen Target. https://arxiv.org/abs/2608.29159

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