Status of the plastic scintillator detector for the HERD experiment

Future satellite experiments for cosmic-ray and gamma-ray detection will employ plastic scintillators to discriminate gamma-rays from charged particles and to identify nuclei up to Iron. The High Energy Cosmic Radiation Detector (HERD) facility will be one of those new experiments and it will be installed onboard the Chinese Tiangong Space Station (TSS). The main goal of the HERD experiment is to detect charged cosmic-rays up to PeVand gamma-rays up to hundred GeVs. The plastic scintillator detector (PSD) surrounds the inner detectors on five sides. For energies above a few GeVs a high detector segmentation is required in order to avoid the back-splash effect, due to the interaction between high energy particles and the innermost calorimeter. Each PSD basic element (bar or tile) is coupled to several Silicon Photomultipliers (SiPMs) for the detection of scintillation light. In 2021 we have performed a beam test campaign to test all the subdetectors of the HERD experiment at CERN PS and SPS. We tested two different PSD prototypes, one with a long bar geometry and the other with a squared tile geometry. In both prototypes two scintillating materials (BC-404 and BC-408) were used. Both the prototypes were equipped with SiPMs of two different sizes (MPPC S14160-3050 and S14160-1315) and they were read-out by the CAEN Citiroc-based board DT5550 W. In this work we will describe the PSD design along with the beam test results.