Cosmogenic Neutron Production in Water at SNO+
SNO+ Collaboration, :, M. Abreu, A. Allega, M. R. Anderson, S. Andringa, S. Arora, D. M. Asner, D. J. Auty, A. Bacon, T. Baltazar, F. Barão, N. Barros, R. Bayes, C. Baylis, E. W. Beier, A. Bialek, S. D. Biller, E. Caden, E. J. Callaghan, M. Chen, S. Cheng, B. Cleveland, D. Cookman, J. Corning, S. DeGraw, R. Dehghani, J. Deloye, M. M. Depatie, C. Dima, J. Dittmer, K. H. Dixon, M. S. Esmaeilian, E. Falk, N. Fatemighomi, R. Ford, S. Gadamsetty, A. Gaur, D. Gooding, C. Grant, J. Grove, S. Hall, A. L. Hallin, D. Hallman, M. R. Hebert, W. J. Heintzelman, R. L. Helmer, C. Hewitt, B. Hreljac, P. Huang, R. Hunt-Stokes, A. S. Inácio, C. J. Jillings, S. Kaluzienski, T. Kaptanoglu, J. Kladnik, J. R. Klein, L. L. Kormos, B. Krar, C. Kraus, C. B. Krauss, T. Kroupová, C. Lake, L. Lebanowski, C. Lefebvre, B. Liggins, V. Lozza, M. Luo, S. Maguire, A. Maio, S. Manecki, J. Maneira, R. D. Martin, N. McCauley, A. B. McDonald, G. Milton, D. Morris, M. Mubasher, S. Naugle, L. J. Nolan, H. M. O'Keeffe, G. D. Orebi Gann, S. Ouyang, J. Page, S. Pal, K. Paleshi, W. Parker, L. J. Pickard, R. C. Pitelka, B. Quenallata, P. Ravi, A. Reichold, S. Riccetto, J. Rose, R. Rosero, J. Shen, J. Simms, P. Skensved, M. Smiley, M. I. Stringer, R. Tafirout, B. Tam, J. Tseng, E. Vázquez-Jáuregui, C. J. Virtue, F. Wang, M. Ward, J. R. Wilson, J. D. Wilson, A. Wright, S. Yang, Z. Ye, M. Yeh, S. Yu, Y. Zhang, K. Zuber
TL;DR
This work measures the cosmogenic muon-induced neutron yield in ultra-pure water with the SNO+ detector, exploiting an average muon energy of $364\,\text{GeV}$ to probe high-energy muon interactions. Using a water Cherenkov configuration and calibration with Am-Be sources, the team employs detailed simulations (GEANT4) and per-event efficiency corrections to extract $Y_n= (3.38^{+0.23}_{-0.30})\times10^{-4}\,\text{cm}^{2}\text{g}^{-1}\mu^{-1}$, validating the FLUKA neutron-production model while highlighting discrepancies with GEANT4. The result, along with the comparison to SNO’s heavy-water measurements, indicates material composition and nuclear structure significantly influence cosmogenic neutron production, with important implications for background modeling in future underground experiments. The study also outlines plans to repeat the measurement in the scintillator phase to enable a direct water–scintillator comparison under the same muon flux, further constraining models of muon-induced backgrounds.
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 $364\,\textup{GeV}$. Using ultra-pure water, we have determined a neutron yield of $Y_{n}=(3.38^{+0.23}_{-0.30})\times10^{-4}\,\textup{cm}^{2}\textup{g}^{-1}μ^{-1}$ at SNO+. Comparison with simulations demonstrates clear agreement with the \textsc{FLUKA} neutron production model, highlighting discrepancies with the widely used \textsc{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.