Measurement of the cosmic ray helium energy spectrum from 70 GeV to 80 TeV with the DAMPE space mission

TL;DR

This paper reports the first observation of a spectral softening in cosmic ray helium nuclei at around 34 TeV using 4.5 years of DAMPE data, revealing new features in the cosmic ray energy spectrum.

Contribution

It provides the first measurement of helium spectrum softening at 34 TeV with high statistics and systematic control, highlighting charge-dependent spectral features.

Findings

Spectral hardening at ~1.3 TeV observed

Spectral softening at ~34 TeV detected with 4.3σ significance

Charge-dependent spectral features suggested

Abstract

The measurement of the energy spectrum of cosmic ray helium nuclei from 70 GeV to 80 TeV using 4.5 years of data recorded by the DArk Matter Particle Explorer (DAMPE) is reported in this work. A hardening of the spectrum is observed at an energy of about 1.3 TeV, similar to previous observations. In addition, a spectral softening at about 34 TeV is revealed for the first time with large statistics and well controlled systematic uncertainties, with an overall significance of $4.3\sigma$. The DAMPE spectral measurements of both cosmic protons and helium nuclei suggest a particle charge dependent softening energy, although with current uncertainties a dependence on the number of nucleons cannot be ruled out.