Sensitivity of the FCC-ee to the decay of a dark photon into a ${\mu }^{+}{\mu }^{-}$ pair

The production of a dark photon $A^{\mathrm{\prime }}$ at the proposed CERN FCC-ee collider is investigated. The study addresses the associated production $e^{+}{e}^{-}\to \gamma A^{\mathrm{\prime }}$ followed by the decay $A^{\mathrm{\prime }}\to {\mu }^{+}{\mu }^{-}$. The 95% CL sensitivity on the mixing between the photon and the dark photon is evaluated in the $m_{A^{\mathrm{\prime }}}$ mass range 0.4-360 GeV, based on a parametrised simulation of the IDEA detector. The study is performed both for prompt and long-lived decays of the $A^{\mathrm{\prime }}$.