Is the DAMPE 1.4 TeV peak real?

In 2017, China’s Dark Matter Particle Explorer (DAMPE) reported a possible peak in the cosmic-ray electron and positron spectrum at 1.4 TeV. The finding, published in Nature, suggested a sharp spectral feature that could indicate exotic physics or nearby astrophysical sources.

The Calorimetric Electron Telescope (CALET) on the International Space Station has now contradicted this result. Using seven years of data with three times higher statistics, CALET reported in Physical Review Letters (2023) that it “does not observe any significant evidence for a narrow spectral feature in the energy region around 1.4 TeV.” The experiments disagree at greater than 4-sigma significance.

The Measurements

Both experiments measure cosmic-ray electrons and positrons from GeV to TeV energies. They agree on a spectral break around 0.9-1 TeV where the flux steepens significantly, consistent with radiative energy losses during particle propagation. However, DAMPE observed an additional narrow peak at 1.4 TeV, while CALET’s higher-statistics measurement shows only smooth spectral steepening.

CALET’s superior energy resolution (better than 2% above 20 GeV) and proton rejection capabilities make it well-suited to detect such features. The experiment analyzed 7.02 million electron candidates above 10.6 GeV collected through 2022.

Current Status

The statistical significance of DAMPE’s original peak was modest, leading some theorists to suggest it could be a statistical fluctuation. CALET’s results support this interpretation, though systematic differences between the experiments beyond the 1.4 TeV region indicate ongoing instrumental challenges in this energy range.

DAMPE continues data collection and analysis. Additional statistics should clarify whether the 1.4 TeV feature persists or diminishes, resolving this discrepancy in cosmic-ray measurements.