An article entitled "Search for Neutrinos from Annihilation of Captured Low-Mass Dark Matter Particles in the Sun by Super-Kamiokande" has been published in Physical Review Letters and has been further selected as an "Editor's Suggestion."
Dark matter is known to be 5-to-6 times more abundant than ordinary matter in the universe, but because it does not produce light its true nature remains largely unknown. However, it is thought to have played an important role in the formation of the structure of the present universe and as a result, detecting dark matter can be a great help in solving its mysteries.
Searches for dark matter are divided into two categories: direct and indirect detection experiments. While the former search for the interaction of dark matter particles with a nucleus in a terrestrial detector, the latter search for ordinary particles produced from the self-annihilation of dark matter particles in places such as the center of the galaxy, in the Milky Way halo, or within the Sun.
Though positive event excesses reported by direct detection experiments have been interpreted as consistent with the interactions from dark matter particles with a mass of about 10 GeV/c2, subsequent searches by both direct and indirect detection experiments have yielded null results.
Accordingly, searches for dark matter particles with masses less than 30 GeV/c2 performed with an independent detection method and a different set of uncertainties are essential to help resolve this conflict.
In the published article the Super-Kamiokande collaboration presents results from a search for neutrinos produced when dark matter particles that are gravitationally trapped within the sun collide with each other. This process is called self-annihilation. Though previous analyses by the collaboration used only high energy muons produced by neutrino interactions in the rock around the detector, the present work includes neutrino interactions that originate within the detector and have much lower energies.
A likelihood method making full use of each event's interaction energy, angle to the sun, and particle type is used to extract a potential signal from the large atmospheric neutrino background. Compared to the previous results the signal acceptance for low mass dark matter particles has been increased by between one and two orders of magnitude in the current analysis.
Using 3903 days of Super-Kamiokande data no significant signal excess was found over the expected atmospheric neutrino background. This result has been interpreted as upper limits on the dark matter interaction cross section with ordinary nucleons under different assumptions about the self-annihilation channel. The limits placed on the spin-dependent interaction cross section below 200 GeV/c2 are the most stringent to date.
Additionally, limits on the spin-independent interactions of dark matter have ruled out a large fraction of positive results from direct detection experiments and new limits for masses below 6 GeV/c2 have been established for specific annihilation channels.