Direct Measurement of the Cosmic-Ray Helium Spectrum from 40 GeV to 250 TeV with the Calorimetric Electron Telescope on the International Space Station

Abstract

We present the results of a direct measurement of the cosmic-ray helium spectrum with the CALET instrument in operation on the International Space Station since 2015. The observation period covered by this analysis spans from October 13, 2015 to April 30, 2022 (2392 days). The very wide dynamic range of CALET allowed to collect helium data over a large energy interval, from ~40 GeV to ~250 TeV, for the first time with a single instrument in Low Earth Orbit. The measured spectrum shows evidence of a deviation of the flux from a single power-law by more than 8$\sigma$ with a progressive spectral hardening from a few hundred GeV to a few tens of TeV. This result is consistent with the data reported by space instruments including PAMELA, AMS-02, DAMPE and balloon instruments including CREAM. At higher energy we report the onset of a softening of the helium spectrum around 30 TeV (total kinetic energy). Though affected by large uncertainties in the highest energy bins, the observation of a flux reduction turns out to be consistent with the most recent results of DAMPE. A Double Broken Power Law (DBPL) is found to fit simultaneously both spectral features: the hardening (at lower energy) and the softening (at higher energy). A measurement of the proton to helium flux ratio in the energy range from 60 GeV/n to about 60 TeV/n is also presented, using the CALET proton flux recently updated with higher statistics.

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Cited by in corpus (16)

• A cosmic-ray database update: CRDB v4.1
• Measurement of the cosmic p+He energy spectrum from 50 GeV to 0.5 PeV with the DAMPE space mission
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• LHAASO protons versus LHAASO diffuse gamma-rays: a consistency check
• Secondary cosmic-ray nuclei in the Galactic halo model with nonlinear Landau damping
• Galactic diffuse emission from radio to ultra-high-energy gamma rays in light of up-to-date cosmic ray measurements
• Very Local Impact on the Spectrum of Cosmic-Ray Nuclei below 100 TeV
• Hadronic cross section measurements with the DAMPE space mission using 20GeV-10TeV cosmic-ray protons and ${}^4$He
• Precise Measurement of the Cosmic Ray Helium Spectrum above 0.1 PeV
• New determination of the neutrino hadronic production cross sections from GeV to beyond PeV energies
• Precision spectral measurements of Chromium and Titanium from 10 to 250 GeV$/n$ and sub-Iron to Iron ratio with the Calorimetric Electron Telescope on the ISS
• Cosmic ray mass composition measurement in the energy range from $10^{16.5}$ eV to $10^{18.5}$ eV observed with the TALE hybrid detector
• LHAASO Galactic Plane $\gamma$-rays Strongly Constrain Heavy Dark Matter
• Analyzing Cosmic Ray Spectral Features: A Numerical Investigation
• Investigation of hadronic cross sections of cosmic ray carbon and oxygen on BGO from 200 GeV to 10 TeV energy at the DAMPE experiment