Research progress of Dark Matter Particle Explorer

Abstract

Quite a lot of astronomical and cosmological observations reveal that dark matter widely exists in our Universe. It occupies nearly 1/4 of the total energy budget of the Universe, and is about 5 times more abundant than the normal matter. The nature of dark matter is one of the most important fundamental questions of modern physics and astronomy. To probe dark matter particles is also highly competitive among many countries around the world. China has launched the Dark Matter Particle Explorer (DAMPE; also known as “Wukong”) to indirectly detect dark matter via high-precision observations of high-energy electrons and gamma-rays. As a high-energy particle detector, the DAMPE data can also be useful for probing the origin and propagation of cosmic rays, which is another century-long problem, and the energetic activities of extreme objects such as black holes and neutron stars. DAMPE has the highest energy resolution for electron and gamma-ray measurements, and the highest electron-proton discrimination capability above TeV energies. Using the data recorded by DAMPE, we obtain by far the most precise measurements of the spectra of cosmic ray electrons and protons, and reveal new spectral features which were not discovered or clarified before. For the total electron plus positron spectrum, the DAMPE result covers an energy range of 25 GeV–4. 6 TeV, which reaches the highest energy among all the space direct detections. A spectral hardening around 50 GeV, and a softening around 0.9 TeV have been revealed by DAMPE. Some hint of fine structures of the spectrum is also shown which requires more data for confirmation or exclusion. The spectral features of the DAMPE electron plus positron spectrum have very interesting and important implications on the origin and distribution of high-energy electron sources. Particularly, the 0.9 TeV break may reveal the fact that sources of TeV electrons distribute discretely in the Galaxy. The energy range coverage of the DAMPE proton spectrum is from 40 GeV to 100 TeV. For the first time, DAMPE measures the proton spectrum up to 100 TeV with a high statistics. Besides the hundreds of GeV spectral hardening, the DAMPE measurement further reveals a clear spectral softening around 14 TeV. The softening feature of the proton spectrum may be an imprint of nearby cosmic ray acceleration sources. Alternatively, the spectral structures of protons may be due to the superposition of multiple source populations. High-energy gamma-rays have also been robustly identified from the DAMPE data. The analysis shows the detection of luminous diffuse emission from the Galactic plane and nearly 250 pointlike sources in the gamma-ray sky, most of which are active galactic nuclei and pulsars. The DAMPE results offer important data in constraining/understanding the properties of dark matter and cosmic rays. We review the design, operation and data analysis of DAMPE in this work, with a focus on the analyses of spectra of cosmic ray electrons and protons.