Measurement of neutron production in atmospheric neutrino interactions at the Sudbury Neutrino Observatory

Author(s): Aharmim, B; Ahmed, SN; Anthony, AE; Barros, N; Beier, EW; Bellerive, A; Beltran, B; Bergevin, M; Biller, SD; Bonventre, R; Boudjemline, K; Boulay, MG; Cai, B; Callaghan, EJ; Caravaca, J; Chan, YD; Chauhan, D; Chen, M; Cleveland, BT; Cox, GA; Dai, X; Deng, H; Descamps, FB; Detwiler, JA; Doe, PJ; Doucas, G; Drouin, P-L; Dunford, M; Elliott, SR; Evans, HC; Ewan, GT; Farine, J; Fergani, H; Fleurot, F; Ford, RJ; Formaggio, JA; Gagnon, N; Gilje, K; Goon, JTM; Graham, K; Guillian, E; Habib, S; Hahn, RL; Hallin, AL; Hallman, ED; Harvey, PJ; Hazama, R; Heintzelman, WJ; Heise, J; Helmer, RL; Hime, A; Howard, C; Huang, M; Jagam, P; Jamieson, B; Jelley, NA; Jerkins, M; Keeter, KJ; Klein, JR; Kormos, LL; Kos, M; Kruger, A; Kraus, C; Krauss, CB; Kutter, T; Kyba, CCM; Land, BJ; Lange, R; Law, J; Lawson, IT; Lesko, KT; Leslie, JR; Levine, I; Loach, JC; MacLellan, R; Majerus, S; Mak, HB; Maneira, J; Martin, RD; Mastbaum, A; McCauley, N; McDonald, AB; McGee, SR; Miller, ML; Monreal, B | Abstract: Neutron production in GeV-scale neutrino interactions is a poorly studied process. We have measured the neutron multiplicities in atmospheric neutrino interactions in the Sudbury Neutrino Observatory experiment and compared them to the prediction of a Monte Carlo simulation using GENIE and a minimally modified version of GEANT4. We analyzed 837 days of exposure corresponding to Phase I, using pure heavy water, and Phase II, using a mixture of Cl in heavy water. Neutrons produced in atmospheric neutrino interactions were identified with an efficiency of $15.3\%$ and $44.3\%$, for Phase I and II respectively. The neutron production is measured as a function of the visible energy of the neutrino interaction and, for charged current quasi-elastic interaction candidates, also as a function of the neutrino energy. This study is also performed classifying the complete sample into two pairs of event categories: charged current quasi-elastic and non charged current quasi-elastic, and $\nu_{\mu}$ and $\nu_e$. Results show good overall agreement between data and Monte Carlo for both phases, with some small tension with a statistical significance below $2\sigma$ for some intermediate energies.