Coherent Elastic Neutrino-Nucleus Scattering at the Japan Proton Accelerator Research Complex

TL;DR

This paper investigates the feasibility and scientific potential of Coherent Elastic Neutrino-Nucleus Scattering (CE$\nu$NS) measurements at the J-PARC MLF, leveraging a 1.3 MW, 3 GeV proton beam and multiple detector technologies. By modeling neutrino production, beam timing, and detailed backgrounds, the study evaluates sensitivities to SM parameters (weak mixing angle, neutrino charge radii, neutron radius) and a range of BSM scenarios (NSI, light Z' mediators, neutrino magnetic moments, and sterile neutrinos) across CsI, Ge, Xe, and Ar targets. The analysis demonstrates that very high-statistics CE$\nu$NS measurements are achievable within a few years, with timing information crucial for flavor discrimination and with flux normalization, quenching factor, and background modeling as the dominant systematics. The work highlights the complementary role of CE$\nu$NS at J-PARC to other neutrino programs (e.g., Hyper-Kamiokande) and the broader impact on nuclear structure and beyond-Standard-Model neutrino physics. Overall, the proposal emphasizes a diversified detector program enabling precise tests of low-energy electroweak physics and novel interactions in a controlled spallation-source environment.

Abstract

The Japan Proton Accelerator Research Complex (J-PARC) currently delivers a 1 MW, 3 GeV proton beam to the Materials and Life Science Experimental Facility (MLF). Power is expected to increase to 1.3 MW, driven by the needs of Hyper-Kamiokande. As a result, the MLF presently provides the highest neutron yield of any spallation source, while potentially holding the best current and foreseeable conditions for Coherent Elastic Neutrino-Nucleus Scattering (CE$ν$NS) experimentation. We explore this potential, using as examples detector technologies presently funded for construction and under development. We quantify their sensitivity to a rich variety of particle physics scenarios, finding that very-high-statistics CE$ν$NS measurements with significant sensitivity to relevant scenarios are feasible at this facility within the next few years.

Figures (13)

• Figure 1: Comparison between past and present (black squares) and future (red diamonds) spallation sources from the perspective of CE$\nu$NS detection, taking as reference the SNS (blue circle) at the time of first observation of this process COHERENT:2017ipa. A hollow square represents J-PARC MLF following the impending upgrade to 1.3 MW (see text).
• Figure 2: Rendition of the Geant4 geometry for the cryogenic CsI detector. Seven CsI crystals within OFHC copper holders, the LAr volume around them (gray), and two (dark gray) 20 $\times$ 20 cm SiPM tiles sipm are visible. Also shown is an example track by a LAr scintillation photon originating from a background event, wavelength-shifted and reflected towards the SiPM panels (see text).
• Figure 3: Left: Subtractable steady-state backgrounds induced in the CsI detector array alongside the expected CE$\nu$NS rate. The reduction in magnitude for these backgrounds due to beam duty time at J-PARC MLF is applied here. Right: Beam-associated backgrounds (non-subtractable) in comparison to the expected CE$\nu$NS signal. Dotted lines indicate their magnitude prior to applying LAr inner veto cuts.
• Figure 4: Beam-associated (non-subtractable) and subtractable steady-state backgrounds in comparison to the expected CE$\nu$NS signal in the Ge detector (see text). The steady-state component is reduced by the beam duty time and expressed in per keV$_{ee}$ units. For a more direct comparison, the rest of spectra should be converted to the same energy scale using the QF for germanium geqf2.
• Figure 5: Lateral cut of the GanESS detector design, consisting of two symmetrical TPCs with the cathode in the center of a stainless steel 316Ti alloy vessel, allowing for operation above 35 bar. Two planes of 19 PMTs each read both the primary scintillation light produced by the events and the amplified signal of the ionised electrons when crossing the electroluminescent regions in the laterals of the detector. This detector allows for operation with any noble gas, in particular argon and xenon which are the gases assumed in this work.