New Search for Dark Matter with Neutrons at Neutrino Detectors

TL;DR

This paper introduces a novel neutron detection method in neutrino detectors for boosted dark matter searches, significantly improving sensitivity and expanding the range of detectable dark matter models.

Contribution

It proposes utilizing knockout neutrons via gamma-ray and neutron coincidence detection in water Cherenkov detectors, a first in dark matter searches with this approach.

Findings

Method increases sensitivity to boosted dark matter by an order of magnitude.

Allows exploration of previously inaccessible light dark-matter models.

Demonstrates projected sensitivity for Hyper-Kamiokande.

Abstract

Large-volume neutrino experiments are ideal for testing boosted dark matter (BDM) scenarios. We propose, for the first time, an approach to utilize knockout neutrons by detecting de-excitation $\gamma$ rays and coincident captured neutrons from dark-matter interactions with bound neutrons in oxygen, while previous studies have focused on knockout-protons and electrons. This method is especially crucial for water \v{C}erenkov detectors, where high proton \v{C}erenkov threshold ($\sim$1 GeV) suppresses signal acceptance. Recently, Super-Kamiokande (SK) was doped with 0.03\% gadolinium (SK-Gd) to enhance neutron tagging efficiency. Using SK-Gd as a target experiment, we demonstrate that this method increases sensitivity to BDM models by an order of magnitude compared to proton-based analysis, and it allows exploration of a wider range of light dark-matter models previously inaccessible with proton-based analysis. We also present the projected sensitivity for the upcoming Hyper-Kamiokande detector.