Using the earth's geomagnetic field to measure ultra-heavy cosmic ray abundances and electron and positron fluxes with CALET

Abstract

The CALorimetric Electron Telescope (CALET) is an imaging calorimeter under construction for launch to the ISS in 2014 designed to measure electron energy spectra from 1 GeV to 20 TeV, detect gamma-rays above 10 GeV, and measure the energy spectra of nuclei from protons through iron up to 1,000 TeV [1]. 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 (r.l.) of tungsten plates read out with 8 planes of interleaved scintillating fibers, and a total absorption calorimeter (TASC) with 27 r.l. of lead tungstate (PWO) logs [2]. CALET can make additional cosmic ray measurements by exploiting the geomagnetic field it will be exposed to in the 51.6° degree inclination orbit on the ISS. The rare nuclei heavier than nickel (Z=28) can be resolved using the CHD and top IMC layers without requiring particle energy determination in the TASC in field regions where the rigidity cutoffs are above minimum ionization in the scintillator, yielding a nearly 4 times increase in geometry factor [3,4]. CALET can also measure the distinct fluxes of cosmic ray positrons and electrons using the East-West effect of particles traveling in the earth's geomagnetic field over an energy band of ∼ 3 - 20 GeV [5].