Helium flux and its ratio to proton flux in cosmic rays measured with CALET on the International Space Station

The CALorimetric Electron Telescope (CALET) is a space-based calorimetric instrument, designed to carry out precision measurements of high energy cosmic rays. Installed on the Japanese Experiment Module – Exposed Facility on the ISS, it is collecting data with excellent performance and no significant interruptions since October 2015. We present the results of a direct measurement of the energy spectrum of cosmic-ray helium, based on about 6.5 years of collected data. It shows significant deviations from a single power law with a progressive hardening around a few hundred GeV followed by a softening in the multi-TeV region. A measurement of the proton to helium flux ratio is also presented. Thanks to the recent update of the CALET proton flux with higher statistics, the p/He ratio is measured with high precision, extending the energy reach of previous measurements with magnetic spectrometers by more than one order of magnitude.