Search for neutrinos associated with solar flare

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 × 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, 1.36×10⁻⁴ 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.