Measurement of the re-entrant lepton spectrum with the High-Energy Particle Detector on board CSES-01

The High-Energy Particle Detector (HEPD-01) is one of the particle detectors installed on board the China Seismo-Electromagnetic Satellite (CSES-01). The instrument consists of different subdetectors, including two planes of double-sided silicon microstrip sensors, a calorimeter constituted by 16 plastic scintillators and a layer of LYSO crystals, and a scintillator veto system surrounding the calorimeter. The detector is dedicated to the measurement of proton (30-200 MeV) and electron (3-100 MeV) fluxes, and their variations induced by short-time perturbations of the radiation belts due to solar, terrestrial, or anthropic phenomena. Although the detector is capable to measure particles with a galactic origin, due to its energy range and to the CSES-01 polar orbit, HEPD collects particles below the local geomagnetic cutoff for a large fraction of its total live time. In this work, the differential spectrum of re-entrant leptons (the downward-moving component of secondary electrons and positrons produced in the interactions of cosmic ray protons with the atmosphere) is measured in the near-equatorial region (altitude about 500 km) in the energy interval between 10 and 100 MeV where there is a lack of recent experimental data.