Search for neutrinos from annihilation of captured low-mass dark matter particles in the Sun by Super-Kamiokande

Super-Kamiokande(SK) can search for weakly interacting massive particles( WIMPs) by detecting neutrinos produced from WIMP annihilationsoccurring inside the Sun. In this analysis, we include neutrino events with interaction vertices in the detector in addition to upward-going muons produced in the surrounding rock. Compared to the previous result, which used the upward-going muons only, the signal acceptances for light (few-GeV/$c^2$ $\sim$ 200-GeV/$c^2$) WIMPsare significantly increased. We fit 3903 days of SK data to search for the contribution of neutrinos from WIMP annihilationin the Sun. We found no significant excess over expected atmospheric-neutrino background and the result is interpreted in terms of upper limits on WIMP-nucleon elastic scattering cross sections under different assumptions about the annihilationchannel. We set the current best limits on the spin-dependent (SD) WIMP-proton cross section for WIMPmasses below 200 GeV/$c^2$ (at 10 GeV/$c^2$, 1.49$\times 10^{-39}$ cm$^2$ for $\chi\chi\rightarrow b \bar{b}$ and 1.31$\times 10^{-40}$ cm$^2$ for $\chi\chi\rightarrow\tau^+\tau^-$ annihilationchannels), also ruling out some fraction of WIMPcandidates with spin-independent (SI) coupling in the few-GeV/$c^2$ mass range.