Search for GUT Monopoles at Super-Kamiokande

TL;DR

This paper reports a search for GUT monopoles using neutrino detection at Super-Kamiokande, setting a flux limit that surpasses previous experimental bounds by several orders of magnitude.

Contribution

The study provides the most stringent monopole flux limit to date by analyzing low energy neutrinos from monopole-catalyzed proton decays at Super-Kamiokande.

Findings

Set a monopole flux limit of < 6.3 x 10^{-24} cm^{-2} s^{-1} sr^{-1} at 90% C.L.

Flux limit is over eight orders of magnitude more restrictive than previous cosmic-ray limits.

Achieved a two orders of magnitude improvement over the Kamiokande experiment.

Abstract

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.