A China-led space science mission provide a tantalizing hint—but not firm evidence—for dark matter. Initial analysis of 1.5 million cosmic rays detections has shown a gap in the spectrum. Something is interfering with these cosmic ray energy signals and it might be the decay of dark matter.
They expect the satellite to last 5 years and it should record more than 10 billion cosmic ray events.
China’s Dark Matter Particle Explorer (DAMPE) was designed to try to fill that gap, by looking for an indirect decay signal of a hypothetical dark matter candidate called weakly interacting massive particles (WIMPs). Researchers launched the spacecraft from the Jiuquan Satellite Launch Center in the Gobi Desert, about 1600 kilometers west of Beijing, in December 2015. Its primary instrument—a stack of thin, crisscrossed detector strips—is tuned to observe the incoming direction, energy, and electric charge of the particles that make up cosmic rays, particularly electrons and positrons, the antimatter counterparts of electrons. Cosmic rays emanate from conventional astrophysical objects, like exploding supernovae in the galaxy. But if dark matter consists of WIMPs, these would occasionally annihilate each other and create electron-positron pairs, which might be detected as an excess over the expected abundance of particles from conventional objects.
In its first 530 days of scientific observations, DAMPE detected 1.5 million cosmic ray electrons and positrons above a certain energy threshold. When researchers plot of the number of particles against their energy, they’d expect to see a smooth curve. But previous experiments have hinted at an anomalous break in the curve. Now, DAMPE has confirmed that deviation. “It may be evidence of dark matter,” but the break in the curve “may be from some other cosmic ray source,” says astrophysicist Chang Jin
High-energy cosmic-ray electrons and positrons (CREs), which lose energy quickly during their propagation, provide a probe of Galactic high-energy processes and may enable the observation of phenomena such as dark-matter particle annihilation or decay. The CRE spectrum has been measured directly up to approximately 2 teraelectronvolts in previous balloon- or space-borne experiments and indirectly up to approximately 5 teraelectronvolts using ground-based Cherenkov γ-ray telescope arrays. Evidence for a spectral break in the teraelectronvolt energy range has been provided by indirect measurements 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 measurements clarifies the behavior 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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