Most precise measurements of cosmic ray proton and helium spectra above TeV


Fig. 1 The charge measurements of DAMPE: 500 GeV (left) and 5 TeV (right). Credit: DAMPE

The Dark Matter Particle Explorer (DAMPE) cooperation reported the precise measurement of the energy spectrum of cosmic ray helium nuclei from 70 GeV to 80 TeV energies on May 18, 2021.


For the very first time, DAMPE exposes a softening structure at about 34 TeV energies in the helium spectrum with a high significance (~4.3σ). Together with the softening energy of the DAMPE proton spectrum, the outcomes follow a charge-dependent softening energy of protons and helium nuclei.

The typical softening is likely an imprint of a close-by cosmic ray source, e.g., a supernova residue. The softening energy, which is most likely Z-dependent for protons and helium nuclei, represents the velocity upper-limit of such a close-by source.

DAMPE, likewise called “Wukong,” is a space satellite committed to high-energy cosmic ray and gamma-ray observations. Besides penetrating the nature of dark matter particles, one of the primary clinical objectives of DAMPE is to specifically determine the energy spectra of cosmic ray particles.

DAMPE has an exceptional energy resolution (for electrons and gamma-rays), a great particle recognition ability, and a fairly big approval, making it well appropriate for the research studies of precise spectral structures of cosmic rays.

Cosmic rays (CRs) are energetic particles originating from external space. They are mainly comprised of nuclei of numerous aspects, together with percentages of electrons/positions, gamma-ray photons, and neutrinos.

Most precise measurements of cosmic ray proton and helium spectra above TeV
Fig. 2 The DAMPE proton spectrum from 40 GeV to 100 TeV (left) and the DAMPE helium spectrum from 70GeV to 80 TeV (right). Credit: DAMPE

Cosmic rays are usually thought to stem from severe astrophysical things, e.g. supernova residue (SNR), accretion by black hole, etc. Therefore, CRs are a unique probe to check out the astrophysical laws under severe environments. The origin, velocity, and proliferation of CRs are really fascinating and essential concerns in contemporary physics and astrophysics, which stay unanswered after a century-long observation and research study.

The energy spectrum of CRs, which represents the relation of particle flux to energy, is anticipated to be a power-law kind according to the canonical shock velocity of particles. Precise measurement of the energy spectrum of CRs is the crucial to comprehending those essential concerns of cosmic ray physics.

Protons and helium nuclei, are the most 2 plentiful parts of cosmic rays, which represent more than 99% in overall cosmic rays. The exceptional charge resolution allows DAMPE to have an effective ability to recognize proton and helium, and specifically determine their spectra respectively. Fig. 1 reveals the exceptional charge measurement of DAMPE at 2 common energies.

Since the launch at completion of 2015, the DAMPE detector has actually been working really stably in-orbit for 4 years. Significant advances in the observations of cosmic ray electrons/positions, protons, and helium nuclei have actually been accomplished. With the constant operation and information collection of DAMPE, it is anticipated that more and more premium information will shed brand-new light on the essential concerns about cosmic ray physics.

With the very first 30 months on-orbit information, the DAMPE cooperation acquired the precise measurement of the energy spectrum of cosmic ray protons from 40 GeV to 100 TeV energies. The DAMPE outcome reveals that the proton spectrum is not suitable with the paradigm of a unique power-law in a large energy variety.

Especially, DAMPE freshly found a spectral “softening” (drop habits) at about 14 TeV energies. The break energy is anticipated to be the velocity limitation of a possible close-by cosmic ray source.

The DAMPE outcome has actually considerably enhanced the measurement precision of helium spectrum in the energy variety above TeV. The spectrum of CR helium reveals a really comparable TeV structure with the one of CR proton, which recommends a typical origin of them.


First finding of China’s DAMPE might clarify dark matter research study


More info:
F. Alemanno et al, Measurement of the Cosmic Ray Helium Energy Spectrum from 70 GeV to 80 TeV with the DAMPE Space Mission, Physical Review Letters (2021). DOI: 10.1103/PhysRevLett.126.201102

Provided by
Chinese Academy of Sciences

Citation:
Most precise measurements of cosmic ray proton and helium spectra above TeV (2021, May 26)
obtained 26 May 2021
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