Synopsis: Antiprotons May Hold Dark Matter Signal

Recently released data on cosmic-ray antiprotons may contain hints of dark matter, as revealed by two new analyses.
Synopsis figure
NASA

One promising way to detect dark matter is to search for “excess” cosmic rays that presumably originate from dark matter (DM) particles annihilating each other in collisions. Two teams have separately analyzed recent data on cosmic-ray antiprotons obtained by the Alpha Magnetic Spectrometer (AMS) experiment. Both groups find indications of an excess of antiprotons that may correspond to a DM particle with a mass of several tens of GeVc2.

Cosmic rays contain a small sprinkling of antimatter particles, such as positrons and antiprotons. Most of these antiparticles are created in “astrophysical” collisions between a high-energy cosmic ray and interstellar gas. However, a small portion could come from DM annihilations or decays. The challenge in identifying such a DM signature is to accurately model the much larger astrophysical background in which the signal is hidden.

In their study, Alessandro Cuoco and collaborators from RWTH Aachen University, Germany, assumed two scenarios—one with and one without DM. They ran simulations for both cases, adjusting different parameters to achieve the best fit to antiproton, proton, and helium cosmic-ray data from AMS and other experiments. They found that a model with a DM particle—in this case one with a mass of 80 GeVc2—provided a better match to the antiproton observations than a model with no DM.

Meanwhile, Ming-Yang Cui from the Chinese Academy of Sciences and colleagues performed an independent analysis based on a slightly different set of assumptions. Their strategy relied on cosmic-ray observations of the boron-to-carbon ratio, which gives an indication of how far cosmic rays travel to reach us. They found that a model with a DM particle of mass between 40 and 60 GeVc2 gave the best fit to the antiproton data. Both these and Cuoco and colleagues’ results are in broad agreement with the dark matter explanation for an observed excess of gamma rays from the center of our Galaxy.

This research is published in Physical Review Letters.

–Michael Schirber

Michael Schirber is a Corresponding Editor for Physics based in Lyon, France.


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