Phys. Rev. Lett. 114, 141301 (2015)

According to the standard model of cosmology, most of the matter in the known universe does not significantly absorb or emit electromagnetic radiation. The favoured explanation for the abundance of such dark matter is weakly interacting massive particles (WIMPs) that pervade the universe, but interact only through gravity and the weak force. Probing matter that interacts so weakly, however, presents significant challenges. The Super-Kamiokande neutrino observatory has now placed strict limits on the possible strength of interactions between protons and WIMPs.

Super-Kamiokande is a cylindrical detector in the Kamioka mine in Japan, which uses photomultiplier tubes to detect Cherenkov radiation emitted when neutrons interact with electrons or nuclei of water. But the flux of neutrinos from the Sun is expected to be dependent on WIMPs: interactions with the Sun's many nuclei should cause WIMPs to lose enough energy to become gravitationally bound and self-annihilate, increasing the neutrino flux. No significant neutrino excess was found after 3,903 days of Super-Kamiokande data, however, restricting the spin-dependent scattering cross-sections of protons and WIMPs with masses below 200 GeV c−2 — ruling out several WIMP candidates.