Cosmogenic Neutron Production in Water at SNO+

TL;DR

This study measures cosmogenic neutron yield in ultra-pure water at SNO+ with high-energy muons, compares results with simulations, and highlights the influence of target material on neutron production.

Contribution

First measurement of neutron yield at SNO+ with high-energy muons, revealing material-dependent differences and validating the FLUKA model over GEANT4.

Findings

Neutron yield at SNO+ is approximately 3.38×10^{-4} cm^2 g^{-1} μ^{-1}.

FLUKA simulation agrees well with measured neutron yield.

Lower neutron yield observed in water compared to heavy water under similar conditions.

Abstract

Accurate measurement of the cosmogenic muon-induced neutron yield is crucial for constraining a significant background in a wide range of low-energy physics searches. Although previous underground experiments have measured this yield across various cosmogenic muon energies, SNO+ is uniquely positioned due to its exposure to one of the highest average cosmogenic muon energies at $364\,\text{GeV}$. Using ultra-pure water, we have determined a neutron yield of $Y_{n}=(3.38^{+0.23}_{-0.30})\times10^{-4}\,\text{cm}^{2}\text{g}^{-1}\mu^{-1}$ at SNO+. Comparison with simulations demonstrates clear agreement with the FLUKA neutron production model, highlighting discrepancies with the widely used GEANT4 model. Furthermore, this measurement reveals a lower cosmogenic neutron yield than that observed by the SNO experiment, which used heavy water under identical muon flux conditions. This result provides new evidence that nuclear structure and target material composition significantly influence neutron production by cosmogenic muons, offering fresh insight with important implications for the design and background modelling of future underground experiments.