Calet: A high energy astroparticle physics experiment on the ISS

CALET (CALorimetric Electron Telescope) is a high energy astroparticle physics experiment planned for a long exposure mission aboard the International Space Station (ISS) by the Japanese Aerospace Exploration Agency, in collaboration with the Italian Space Agency (ASI) and NASA. The main science goal is high precision measurements of the inclusive electron (+positron) spectrum below 1 TeV and the exploration of the energy region above 1 TeV, where the shape of the high end of the spectrum might unveil the presence of nearby sources of acceleration. CALET has been designed to achieve a large proton rejection capability (>105) with a fine grained imaging calorimeter (IMC) followed by a total absorption calorimeter (TASC), for a total thickness of 30 X0 and 1.3 proton interaction length. With an excellent energy resolution and a lower background contamination with respect to previous experiments, CALET will search for possible spectral signatures of dark matter with both electrons and gamma rays. CALET will also measure the high energy spectra and relative abundance of cosmic nuclei from proton to iron and will detect trans-iron elements up to Z ∼ 40. The charge identification of individual nuclear species is performed by a dedicated module (CHD) at the top of the apparatus and by multiple dE/dx measurements in the IMC. With a large exposure and high energy resolution, CALET will be able to verify and complement the observations of CREAM, PAMELA and AMS-02 on a possible deviation from a pure power-law of proton and He spectra in the region of a few hundred GeV and to extend the study to the multi-TeV region. CALET will also contribute to clarify the present experimental picture on the energy dependence of the boron/carbon ratio, below and above 1 TeV/n, thereby providing valuable information on cosmic-ray propagation in the galaxy. Gamma-ray transients will be studied with a dedicated Gamma-ray Burst Monitor (GBM).