The Positron Annihilation into Dark Matter Experiment (PADME) aims to search for a dark photon
(𝐴′) produced in the process 𝑒+𝑒− → 𝛾𝐴′. It uses the positron beam provided by the DAΦNE
LINAC, maximum energy 550 MeV, at the Frascati National Laboratory of INFN. The aim of
the experiment is to evaluate the missing mass of single-photon final states following positron
annihilation on the electrons of a thin target. To measure such a reaction, the PADME apparatus
has been built. It consists of a small-scale detector composed of the following parts:
• a diamond active target, to measure position and intensity of the beam in each single bunch;
• a beam monitor system consisting of two different silicon-pixel detectors;
• a spectrometer, to measure the charged particle momenta in the range 50-400 MeV;
• a dipole magnet, to deflect the primary positron beam out of the spectrometer and calorimeter
and to allow momentum analysis;
• a finely segmented, high resolution electromagnetic calorimeter, to measure 4-momenta
and/or veto final state photons.
Each element has specific requirements that are stringent and sometimes at the limit of present
technology.