Performance of the PADME calorimeter prototype at the DA$\Phi$NE BTF
  The PADME experiment at the DA$\Phi$NE Beam-Test Facility (BTF) aims at searching for invisible decays of the dark photon by measuring the final state missing mass in the process $e^+e^- \to \gamma+ A'$, with $A'$ undetected. The measurement requires the determination of the 4-momentum of the recoil photon, performed using a homogeneous, highly segmented BGO crystals calorimeter. We report the results of the test of a 5$\times$5 crystals prototype performed with an electron beam at the BTF in July 2016. 
M. Raggi, V. Kozhuharov, P. Valente, F. Ferrarotto, E. Leonardi, G.   Organtini, L. Tsankov, G. Georgiev, J. Alexander, B. B...
physics.ins-det hep-ex