Search for Light WIMPs Captured in the Sun Using Contained Events in Super-Kamiokande

Super-Kamiokande can search for dark matter by detecting neutrinos and muons which are produced by WIMP pair annihilations occurring inside the Sun. The huge gravity and hydrogen-rich composition of the Sun combined with high sensitivity of Super-Kamiokande for low energy (few GeV) neutrinos allow us good sensitivity to light (few GeV to few 10 GeV) WIMP dark matter, especially for spin-dependent coupling ones. In this analysis, we increased signal acceptance by using fully-contained and partially-contained neutrino events added to up-going muons in Super-Kamiokande. We performed least-squares fitting to use energy, direction and flavor information. We used 3903 days of Super-Kamiokande I-IV data to find the allowed contribution of WIMP-induced neutrino events added to large background of atmospheric neutrino events. As a result, we found no signal observed and the null result is interpreted as upper limit on the spin-dependent WIMP-proton elastic scattering cross-section for χχ → bb̄ and χχ → τ+τ− WIMPannihilation channels. We set current best limit for WIMP mass below 100 GeV.