Search for GUT monopoles at Super-Kamiokande

Abstract GUT monopolescaptured by the Sun’s gravitation are expected to catalyze proton decaysvia the Callan–Rubakov process. In this scenario, protons, which initially decay into pions, will ultimately produce ν e , ν μ and ν ¯ μ . 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 limitof F M ( σ 0 / 1 mb ) 6.3 × 10 - 24 ( β M / 10 - 3 ) 2 cm - 2 s - 1 sr - 1 at 90% C.L., where β M is the monopolevelocity in units of the speedof lightand σ 0 is the catalysis cross section at β M = 1 . The obtained limit is several orders of magnitude more stringent than the current best cosmic-ray supermassive monopole flux limitfor β M 10 - 2 and also two orders of magnitude lower than the result of the Kamiokande experiment, which used a similar detection method.