Direct detection of a break in the teraelectronvolt cosmic-ray spectrum of electrons and positrons

Abstract

High-energy cosmic-ray electrons and positrons (CREs), which lose energy quickly during their propagation, provide a probe of Galactic high-energy processes1,2,3,4,5,6,7 and may enable the observation of phenomena such as dark-matter particle annihilation or decay8,9,10. The CRE spectrum has been measured directly up to approximately 2 teraelectronvolts in previous balloon- or space-borne experiments11,12,13,14,15,16, and indirectly up to approximately 5 teraelectronvolts using ground-based Cherenkov γ-ray telescope arrays17,18. Evidence for a spectral break in the teraelectronvolt energy range has been provided by indirect measurements17,18, although the results were qualified by sizeable systematic uncertainties. Here we report a direct measurement of CREs in the energy range 25 gigaelectronvolts to 4.6 teraelectronvolts by the Dark Matter Particle Explorer (DAMPE)19 with unprecedentedly high energy resolution and low background. The largest part of the spectrum can be well fitted by a ‘smoothly broken power-law’ model rather than a single power-law model. The direct detection of a spectral break at about 0.9 teraelectronvolts confirms the evidence found by previous indirect measurements17,18, clarifies the behaviour of the CRE spectrum at energies above 1 teraelectronvolt and sheds light on the physical origin of the sub-teraelectronvolt CREs.

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Figure 1: Discrimination between electrons and protons in the BGO instrument of DAMPE.
Figure 2: The CRE spectrum (multiplied by E3) measured by DAMPE.

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Acknowledgements

The DAMPE mission is funded by the strategic priority science and technology projects in space science of the Chinese Academy of Sciences. In China the data analysis was supported in part by the National Key R&D Program of China (number 2016YFA0400200), the National Basic Research Program of China (number 2013CB837000), the National Natural Science Foundation of China (numbers 11525313, 11622327 and U1738206) and the 100 Talents Program of Chinese Academy of Sciences. In Europe the activities and the data analysis are supported by the Swiss National Science Foundation (SNSF), Switzerland; the National Institute for Nuclear Physics (INFN), Italy.

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This work is the result of the contributions and efforts of all the participating institutes, under the leadership of Purple Mountain Observatory, the Chinese Academy of Sciences. All authors have reviewed, discussed, and commented on the present results and on the manuscript. In line with collaboration policy, the authors are listed alphabetically.

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Reviewer Information Nature thanks D. Hooper and the other anonymous reviewer(s) for their contribution to the peer review of this work.

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Extended data figures and tables

Extended Data Figure 1 Comparison of the flight data and the Monte Carlo simulations of the ζ distributions.

All events have deposited energies between 500 GeV and 1 TeV in the BGO calorimeter. The error bars (±1σ) represent statistical uncertainties. As for the Monte Carlo (MC) simulation data, the black, green and red histograms represent the electrons, the protons and their sum, respectively.

Extended Data Figure 2 Ratios of the ζ values calculated from the P- and N-side readout data.

The events have deposited energies between 500 GeV and 1 TeV in the BGO calorimeter. The error bars (±1σ) represent statistical uncertainties. The red line represents a Gaussian fit to the data points. The mean of the ratios is 1.015 ± 0.002 and σ is 0.110 ± 0.005.

Extended Data Figure 3 Ratios of the energies reconstructed with the P- and N-side readout data.

All events have deposited energies between 500 GeV and 1 TeV in the BGO calorimeter. The error bars (±1σ) represent statistical uncertainties. The red line represents a Gaussian fit to the data, with a mean of 1.005 ± 0.005 and a σ of 0.016 ± 0.001.

Extended Data Figure 4 Comparison of two spectral models for the DAMPE CRE spectrum.

The dashed and solid lines show the best-fitting results of the single power-law and smoothly broken power-law models, respectively.

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DAMPE Collaboration., Ambrosi, G., An, Q. et al. Direct detection of a break in the teraelectronvolt cosmic-ray spectrum of electrons and positrons. Nature 552, 63–66 (2017). https://doi.org/10.1038/nature24475

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