Measurement of the re-entrant all-electron spectrum by the High-Energy Particle Detector on board the China Seismo-Electromagnetic Satellite

Interactions of primary cosmic rays with residual atmospheric nuclei produce secondary leptons through the decay chain of short-lived pions. Even though generated with an upward direction, a fraction of these secondary electrons and positrons is bent back downward towards the Earth by the geomagnetic field lines (hence they are called re-entrant albedo). In this paper, we report on a new measurement of the re-entrant all-electron differential flux in the energy range 10-100 MeV, performed by the High-Energy Particle Detector (HEPD-01) on board the China Seismo-Electromagnetic Satellite (CSES-01) in the near-equatorial region at about 500 km altitude between 2018 and 2022. This analysis focuses on the re-entrant all-electron spectrum that covers the low energy interval in a geographical region characterized by a substantial lack of recent experimental data and can contribute to a more accurate definition of secondary electron and positron population distribution and refine the radiation models in the Earth's magnetosphere.