Dark Matter Particle Explorer reports the most precise measurement of cosmic ray proton spectrum from TeV-100 TeV
Protons, the nuclei of hydrogen atoms, are the most abundant component of cosmic rays. Precise measurements of the proton energy spectrum are the key to understanding those fundamental questions of cosmic ray physics. Due to the block of the atmosphere, the direct measurement of cosmic rays needs to be done in space, via high-altitude balloon-borne experiments or space-borne satellites. For a long time the data quality of such measurements is limited by either low statistics or narrow energy-band coverage.
The Dark Matter Particle Explorer (DAMPE), also known as Wukong, is a space satellite dedicated to high-energy cosmic ray and gamma-ray observations. Besides probing the nature of dark matter particles, one of the main scientific goals of DAMPE is to precisely measure the energy spectra of cosmic ray particles. DAMPE has an excellent energy resolution (for electrons and gamma-rays), a very good particle identification capability, and a reasonably large acceptance, making it well suitable for the studies of precise spectral structures of cosmic rays.
On September 28, 2019, the DAMPE collaboration reported the precise measurement of the energy spectrum of cosmic ray protons from 40 GeV to 100 TeV energies in the magazine Science Advances. This is the first time to measure the spectrum up to 100 TeV energies in space with a very large statistics. The maximum energy is nearly 50 times higher than that achieved by the Alpha Magnetic Spectrometer (AMS), and 10 times higher than the Calorimetric Electron Telescope (CALET).
Fig. 1 The 40 GeV-100 TeV energy spectrum of cosmic ray protons measured by DAMPE (red dots). (Image by YUAN Qiang)
The DAMPE result confirms the “hardening” (upturn feature in Fig. 1) feature around hundreds of GeV energies revealed previously. Most importantly, DAMPE newly discovered a spectral “softening” (drop behavior) at about 14 TeV energies. This spectral softening is likely an imprint of a nearby cosmic ray source, e.g., a supernova remnant (see Fig. 2 for a model fitting). The break energy is expected to be the acceleration limit of such a source. The DAMPE result thus provides important data to understand the origin and acceleration of cosmic rays.
Fig. 2 A model to fit the DAMPE proton spectrum. (Image by YUAN Qiang)