Missing energy signature from invisible decays of dark photons at the CERN SPS

Understand

The dark photon ($A'$) production through the mixing with the bremsstrahlung photon from the electron scattering off nuclei can be accompanied by the dominant invisible $A'$ decay into dark-sector particles.

• In this work we discuss the missing energy signature of this process in the experiment NA64 aiming at the search for $A'\to invisible$ decays with a high-energy electron beam at the CERN SPS.
• We show the distinctive distributions of variables that can be used to distinguish the $A'\to invisible$ signal from background.
• The results of the detailed simulation of the detector response for the events with and without $A'$ emission are presented.