With the support of National Natural Science Foundation of China (Grant Nos. 11921003，11622327， 12003076，11722328，11851305，U1738205，U1738206，U1738207，U1738208，U1738127), the international collaboration team of Dark Matter Particle Explorer (DAMPE), led by Purple Mountain Observatory, Chinese Academy of Sciences, measured precisely the energy spectrum of cosmic ray helium nuclei from 70 GeV to 80 TeV energies and revealed clearly a spectral softening around 34 TeV. The paper entitled “Measurement of the cosmic ray helium spectrum from 70 GeV to 80 TeV with the DAMPE space mission” was recently published in Physical Review Letters. See the link http://dx.doi.org/10.1103/PhysRevLett.126.201102

Cosmic rays are energetic particle flow originating from the outer space. They are expected to be originated from extreme astrophysical environments like the remnants of supernova explosionsor the accretions of black holes, and thus are messengers to astrophysical environments and physical laws in such extreme conditions. The origin, acceleration, propagation, and interactions of cosmic rays remain big mysteries even after more than 100 years of the first discovery of cosmic rays. DAMPE is China’s first high-energy particle detector whose main scientific goals are the indirect detection of dark matter particles and the study of cosmic ray physics. Compared with other similar detectors worldwide, DAMPE is superior at the wide energy range coverage, the high energy resolution, and the high capability of particle identification, making DAMPE one of the best instruments for measurements of high-energy electrons/positrons and cosmic ray nuclei.

Using the first four years of data, the DAMPE collaboration team obtained the precise energy spectrum of cosmic ray helium nuclei from 70 GeV to 80 TeV energies. Compared with previous measurements, the precision of DAMPE spectrum is significantly higher above TeV energies. The DAMPE results reveal a new softening feature of the spectrum at 34 TeV, with a significance of 4.3σ. The similarity between the helium spectrum and the proton spectrum (DAMPE collaboration, 2019, Sci. Adv., 5, eaax3793) implies a common origin of those cosmic ray particles, which may be imprints of a nearby source.

DAMPE’s paper has been selected as an Editors’ Suggestion of Physical Review Letters. The editorial in Physics commented that DAMPE has made the most precise measurements of galactic cosmic rays to date, found spectral features that don’t match predictions, and could help researchers uncover the origin of cosmic rays. Since 2017, the DAMPE collaboration team achieved big progresses in the spectral measurements of cosmic ray electrons and positrons, protons, and helium nuclei, indicating that DAMPE has become one of the best instruments for space direct detection of particles. DAMPE continues its stable operation in space and keeps on accumulating high-quality data. It is expected that DAMPE can make even bigger contributions to uncovering eventually the mysteries of cosmic ray origin and acceleration.

Figure 1 Cosmic ray helium spectrum measured by DAMPE, compared with other measurements.