CALET positron/electron measurements using the geomagnetic field

The CALorimetric Electron Telescope (CALET) is under construction for launch to the International Space Station (ISS) in 2014, and consists of the main calorimeter (CAL) instrument and a dedicated Gamma-ray Burst Monitor (CGBM). The primary science goals of the CAL are to measure electron energy spectra from 1 GeV to 20 TeV, to detect gamma-rays above 10 GeV, and to measure the energy spectra of nuclei from protons through iron up to 1,000 TeV. In this paper we describe how Earth’s geomagnetic field at the 51.6^◦ inclination orbit of the ISS can be used to allow CAL to measure the distinct electron and positron fluxes. The positron to electron ratio has been seen to rise above ~ 10 GeV by previous experiments (HEAT, AMS), and more recently to continue to increase to higher energies (~ 80 GeV for PAMELA, ~ 200 GeV for Fermi, and ~ 350 GeV with the best statistics for AMS-02). Utilizing the Earth shadow of the geomagnetic field the CAL will be able to distinguish electrons and positrons above an energy threshold of ~ 3 GeV up to ~ 20 GeV with favorable statistics compared to previous measurements before AMS-02, which includes the energy range where the positron to electron ratio turns over.