First Study of Neutron Tagging with a Water Cherenkov Detector

TL;DR

This paper presents the first neutron tagging study in a large water Cherenkov detector, evaluating efficiency and background, with potential applications in neutrino source identification.

Contribution

It introduces a novel neutron tagging technique in water Cherenkov detectors using GdCl3, demonstrating its effectiveness and background suppression capabilities.

Findings

Neutron tagging efficiency of 66.7% in Gd-doped water for events above 3 MeV.

Background probability for neutron tagging is 2×10⁻⁴ in Gd-doped water.

Potential to identify neutrino sources via delayed coincidence detection.

Abstract

A first study of neutron tagging is conducted in Super--Kamiokande, a 50,000-ton water Cherenkov detector. The tagging efficiencies of thermal neutrons are evaluated in a 0.2 % GdCl$_{3}$-water solution and pure water. They are determined to be, respectively, 66.7 % for events above 3 MeV and 20 % with corresponding background probabilities of 2 $\times$ 10$^{-4}$ and 3 $\times$ 10$^{-2}$. This newly developed technique may enable water Cherenkov detectors to identify $\bar \nu_{e}$'s geological or astrophysical sources as well as those produced by commercial reactors via the delayed coincidence scheme.