Dark photon production through positron annihilation in beam-dump experiments

Abstract

High energy positron annihilation is a viable mechanism to produce dark photons ($A^{\prime }$). This reaction plays a significant role in beam-dump experiments using experiments using multi-GeV electron-beams on thick targets by enhancing the sensitivity to $A^{\prime }$ production. The positrons produced by the electromagnetic shower can produce an $A^{\prime }$ via non-resonant ($e^{+}+e^{-}\to \gamma +A^{\prime }$) and resonant ($e^{+}+e^{-}\to A^{\prime }$) annihilation on atomic electrons. For visible decays, the contribution of resonant annihilation results in a larger sensitivity with respect to limits derived by the commonly used $A^{\prime }$-strahlung in certain kinematic regions. When included in the evaluation of the E137 beam-dump experiment reach, positron annihilation pushes the current limit on $\epsilon$ downwards by a factor of two in the range 33 MeV/c${}^2<m_{A^{\prime }}<120$ MeV/c${}^2$.

Comments: 9 pages, 7 figures