First measurement of flux of the neutron background induced by accelerated neutrinos at the J-PARC facility
Abstract
This article reports the measurement of the neutron background flux accidentally induced by the neutrino beam at the J-PARC facility in Japan. In particular, neutrino-nucleus neutral-current quasi-elastic (NCQE) scattering events, ν (ν̅)+N→ν (ν̅)+N', can be obscured by a massive background of neutron-nucleus scattering events. The neutrons are produced within the materials (such as sand and concrete) located between the beam dump and the experimental area where the detectors are placed. We measured the accidental neutron events at the J-PARC neutrino facility using BGO and liquid scintillation detectors, with a plastic scintillation detector serving as an active veto counter. Based on a neutrino-mode data set of 2.972 × 1020 POT, we observed 88 neutron-induced recoil proton events within an electron-equivalent recoil energy range of 0.98-11.60 MeVee, selected via pulse-shape discrimination in the liquid scintillation detector. Accounting for the detection efficiency and resolution, and through comparison with simulations, the neutron flux was determined to be[1.45+0.22−0.24 (stat.) ± 0.55 (sys.)] × 10−7 cm−2 s−1POT−1,assuming an exponential neutron energy spectrum. This result will contribute to the evaluation of neutron backgrounds for neutrino experiments at the J-PARC facility.
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BibTeX
@misc{ito2026first,
title = {{First measurement of flux of the neutron background induced by accelerated neutrinos at the J-PARC facility}},
author = {Hiroshi Ito and Ryo Shibayama and Chisako Ise and Akihiro Minamino and Yusuke Koshio and Masaki Ishitsuka},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2607.02783},
eprint = {2607.02783},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2607.02783},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - First measurement of flux of the neutron background induced by accelerated neutrinos at the J-PARC facility
AU - Hiroshi Ito
AU - Ryo Shibayama
AU - Chisako Ise
AU - Akihiro Minamino
AU - Yusuke Koshio
AU - Masaki Ishitsuka
PY - 2026
DA - 2026/10/16
PB - arXiv
DO - 10.48550/arxiv.2607.02783
UR - https://arxiv.org/abs/2607.02783
AB - This article reports the measurement of the neutron background flux accidentally induced by the neutrino beam at the J-PARC facility in Japan. In particular, neutrino-nucleus neutral-current quasi-elastic (NCQE) scattering events, ν (ν̅)+N→ν (ν̅)+N', can be obscured by a massive background of neutron-nucleus scattering events. The neutrons are produced within the materials (such as sand and concrete) located between the beam dump and the experimental area where the detectors are placed. We measured the accidental neutron events at the J-PARC neutrino facility using BGO and liquid scintillation detectors, with a plastic scintillation detector serving as an active veto counter. Based on a neutrino-mode data set of 2.972 × 10^20 POT, we observed 88 neutron-induced recoil proton events within an electron-equivalent recoil energy range of 0.98-11.60 MeV_ee, selected via pulse-shape discrimination in the liquid scintillation detector. Accounting for the detection efficiency and resolution, and through comparison with simulations, the neutron flux was determined to be[1.45^+0.22_−0.24 (stat.) ± 0.55 (sys.)] × 10^−7 cm^−2 s^−1POT^−1,assuming an exponential neutron energy spectrum. This result will contribute to the evaluation of neutron backgrounds for neutrino experiments at the J-PARC facility.
ER -