Predicted CALET measurements of electron and positron spectra from 3 to 20 GeV using the geomagnetic field

The CALorimetric Electron Telescope (CALET) is an imaging calorimeter under construction for launch to the ISS in 2014 for a planned 5 year mission. CALET consists of a charge detection module (CHD) with two segmented planes of 1 cm thick plastic scintillator, an imaging calorimeter (IMC) with a total of 3 radiation lengths (X∘X∘) of tungsten plates read out with 8 planes of interleaved scintillating fibers, and a total absorption calorimeter (TASC) with 27 X∘X∘ of lead tungstate (PWO) logs. The primary objectives of the experiment are to measure the electron e-+e+e-+e+ 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 1000 TeV. In this paper we describe how the geomagnetic field at the 51.6°° inclination orbit of the ISS can be used to allow CALET to measure the distinct electron and positron fluxes. The positron fraction has been seen to rise above ∼10∼10 GeV by previous experiments (HEAT, AMS-01), and more recently to continue to increase to higher energies (∼80∼80 GeV for PAMELA, ∼200∼200 GeV for Fermi and ∼350∼350 GeV with the best statistics for AMS-02). Utilizing the geomagnetic cutoff, CALET will be able to distinguish electrons and positrons in the ∼3∼3–20 GeV energy range where the positron fraction turns upward to complement existing high statistics measurements.