An Indirect Search for Light Dark Matter Annihilations in the Earth at the Super Kamiokande Detector

Abstract

The nature of Dark Matter is one of the several greatest puzzles of our present understanding of the universe. While many candidates have been proposed, ranging from light axions to planetary size objects, the elementary particle physics community favorite remains the Weakly Interacting Massive Particle, or WIMP. WIMPs might be “directly detected” by scattering in heavily shielded laboratory detectors, or “indirectly” by observation of the neutrino annihilation products of gravitationally trapped WIMP pairs. Herein we pursue the latter approach employ- ing about 15 years of records from the observed neutrino interactions in the Super- Kamiokande detector in Japan. These data are dominated by electron and muon neutrinos of energies in the few GeV range, spawned from cosmic radiation striking the Earth’s atmosphere. We then search for an additive component to this flux, which could arise from WIMP annihilations in the Earth’s core. We find no significant ex- cess, and so employ that result to set limits on the WIMP-nucleon scattering cross section. Our lowest 90% C.L. exclusion limit on the dark matter-nucleon scattering cross section is for the XX → τ +τ− channel, with a value of σSI = 5.57 × 10−6pb for dark matter mass of 10 GeV, and σSI = 5.27 × 10−8pb, at 50 GeV. The spin independent limits from SuperK dominate world limits for some lower mass and annihilation channel combinations.