  The PADME experiment, hosted at the Laboratori Nazionali di Frascati in
Italy, is dedicated to the dark photon search. It looks for the reaction
$e^{+}\,e^{-}\rightarrow A'\,\gamma$, where $A'$ indicates the dark photon. The
$550\,\text{MeV}$ positrons beam that impinges on electrons, coming from an
active diamond target, allows to scan $A'$ masses up to $23.7\,\text{MeV}$. In
this context, the segmented electromagnetic calorimeter plays a fundamental
role, since it measures the final photon four-momentum. It consists of $616$
BGO crystals displaced in a cylindrical shape of $\approx29\,\text{cm}$ radius
with a central square hole of $5$ crystals side, to let Bremsstrahlung
radiation pass, to limit the calorimeter trigger rate. Each crystal is read by
a HZC XP1911 type B photomultipliers and their signal is digitised by means of
a CAEN V1742 board, taking $1024$ samples at $1\,\text{GS/s}$. Here we report
in detail the solutions adopted for the calorimeter together with the results
obtained in tests performed on a small prototype and on single scintillating
units.

Instrumentation and Detectors;High Energy Physics - Experiment