The Anticoincidence System of Space-Based Gamma-Ray Telescope GAMMA-400, Test Beam Studies of Anticoincidence Detector Prototype with SiPM Readout

The GAMMA-400 gamma-ray telescope is planned for the launch at the end of 2026 on the Navigator service platform designed by Lavochkin Association on an elliptical orbit with following initial parameters: an apogee similar to 300 000, a perigee similar to 500 km, a rotation period similar to 7 days and inclination of 51.4 degrees. The apparatus is expected to operate for more than 5 years, reaching an unprecedented sensitivity for the search of dark matter signatures and the study of the unresolved and so far unidentified gamma-ray sources. The segmented anticoincidence counters surround the converter-tracker and calorimeter of the telescope with the purpose of vetoing to assure a clean track reconstruction and charged particle background suppression. The anticoincidence detector prototype based on long BC-408 scintillator with silicon photomultipliers readout was tested using 300-MeV positron beam of synchrotron C-25P PAKHRA of Lebedev Physical Institute. The measurement setup, design concepts for the prototype detector together with test results are discussed.