GUT monopoles captured by the Sun's gravitation are expected to catalyze proton decays via the Callan-Rubakov process. In this scenario, protons, which initially decay into pions, will ultimately produce \nu_{ e}, \nu_{ \mu} and \bar{ \nu}_{ \mu}. After undergoing neutrino oscillation, all neutrino species appear when they arrive at the Earth, and can be detected by a 50,000 metric ton water Cherenkov detector, Super-Kamiokande (SK). A search for low energy neutrinos in the electron total energy range from 19 to 55 MeV was carried out with SK and gives a monopole flux limit of F_M(\sigma_0/1 mb) < 6.3 \times 10^{ -24} (\beta_M/10^{ -3})^2 cm^{ -2} s^{ -1} sr^{ -1} at 90% C.L., where \beta_M is the monopole velocity in units of the speed of light and \sigma_0 is the catalysis cross section at \beta_M=1. The obtained limit is more than eight orders of magnitude more stringent than the current best cosmic-ray supermassive monopole flux limit, F_M < 1 \times 10^{ -15} cm^{ -2} s^{ -1} sr^{ -1} for \beta_M < 10^{ -3} and also two orders of magnitude lower than the result of the Kamiokande experiment, which used a similar detection method.
Categories: hep-ex astro-ph.HE astro-ph.SR