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

Abstract

The CALorimetric Electron Telescope (CALET) is an imaging calorimeter under construction for launch to the ISS in 2014 for a planned 5year mission. CALET consists of a charge detection module (CHD) with two segmented planes of 1cm thick plastic scintillator, an imaging calorimeter (IMC) with a total of 3 radiation lengths (X∘) of tungsten plates read out with 8 planes of interleaved scintillating fibers, and a total absorption calorimeter (TASC) with 27 X∘ of lead tungstate (PWO) logs. The primary objectives of the experiment are to measure the electron e-+e+ energy spectra from 1GeV to 20TeV, to detect gamma-rays above 10GeV, and to measure the energy spectra of nuclei from protons through iron up to 1000TeV. 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 ∼10GeV by previous experiments (HEAT, AMS-01), and more recently to continue to increase to higher energies (∼80GeV for PAMELA, ∼200GeV for Fermi and ∼350GeV with the best statistics for AMS-02). Utilizing the geomagnetic cutoff, CALET will be able to distinguish electrons and positrons in the ∼3–20GeV energy range where the positron fraction turns upward to complement existing high statistics measurements.