Kamioka Observatory

We developed a three-dimensional gaseous tracking device, and performed a direction-sensitive dark matter search in a surface laboratory. By using 150 Torr carbon-tetrafluoride (CF4gas), we obtained a sky map drawn with the recoil directions of the carbon and fluorine nuclei, and set the first limit on the spin-dependent WIMP (Weakly Interacting Massive Particles)proton cross section by a direction-sensitive method.

Super-Kamiokande (SK) will be upgraded, to become SuperK-Gd, in order to be able to detect thermal neutrons. This will be achieved by dissolving 0.2$\%$ of gadolinium (Gd) sulfate in the otherwise ultra-pure SK water. Gd has the largest cross-section for thermal neutron capture and emits a gamma cascade of about 8 MeV. This cascade is detected with much higher efficiency than the capture on protons which produces a single gamma of 2.2 MeV. EGADS, a 200-ton water Cherenkov detector, was constructed using the same materials as SK and was the test ground for the future SuperK-Gd upgrade. Thanks to the extensive studies at EGADS the SuperK-Gd project was approved in June 2015. In this talk, we will report about the ongoing studies for SuperK-Gd and the plans for the refurbishment of SK.

Importance of search for neutrinos generated during solar flares has been discussed for last 60~years, however, neutrinos associated with solar flares~(solar flare neutrinos) have not been obserbed yet. Since neutrinos are not affected by interplanetary magnetic field, solar flare neutrinos would provide us with information about a particle acceleration mechanism in solar flares. According to some theoretical predictions, flux of the solar flare neutrino would depend on the releasing energy and the location where solar flares ocurr on the Sun surface. Typical predicted probability of detection by Super-Kamiokande (SK) detector is $8.5 \times 10^{-1}$ event/flare for a solar flare which occurs on the opposite side of Sun surface from the earth (invisible side). On the other hands, $1.36 \times 10^{-4}$ event/flare would be predicted for the other side (visible side). To minimize background for the solar flare neutrino searches, data of solar satellites (GOES, RHESSI, and Geotail) were analyzed and time windows for solar flare neutrino searches on the visible side were defined. Coronal Mass Ejection event catalogs were used to determine the search windows for solar flare neutrinos on the invisible side of the Sun. SK is the world's largest underground water Cherenkov detector. The SK experiment has been started the measurement of neutrinos since 1996. The results of solar flare neutrino searches using data sets from SK-I to SK-IV are presented.