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Prospects for Exploring Non-Standard Neutrino Properties with Argon-Based CEvNS Experiments

This paper evaluates the potential of argon-based Coherent Elastic Neutrino-Nucleus Scattering (CEvNS) experiments at major facilities like ORNL, LANL, and Fermilab to perform precision tests of Standard Model electroweak parameters and probe non-standard neutrino properties, including electromagnetic moments and non-standard interactions.

Original authors: Sam Carey, Vishvas Pandey

Published 2026-07-16

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CC BY 4.0

Original authors: Sam Carey, Vishvas Pandey

Original paper licensed under CC BY 4.0 (http://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

Imagine the universe is filled with ghostly messengers called neutrinos. These particles are so shy and light that they can zip right through a planet without bumping into anything, making them incredibly hard to catch. For decades, scientists have been trying to figure out exactly how these ghosts interact with the rest of the world. The standard rulebook of physics, known as the Standard Model, predicts that neutrinos should occasionally bump into the center of an atom (the nucleus) and bounce off, but because the atom is so heavy and the neutrino is so light, the atom barely shudders. It's like a fly hitting a bowling ball; the bowling ball moves, but you need incredibly sensitive equipment to see it wiggle. This tiny wobble is called "Coherent Elastic Neutrino-Nucleus Scattering" (CEvNS). Scientists care about this because if they can measure these wobbles perfectly, they can check if the Standard Model is telling the whole truth or if there are hidden rules of nature—new physics—hiding in the shadows.

This paper is like a blueprint for a new generation of ghost-hunting traps made of liquid argon. The authors, S. Carey and V. Pandey, didn't build these traps themselves; instead, they used powerful computer simulations to predict how well existing and future detectors would work. They focused on four specific setups: two currently running or being upgraded at Oak Ridge National Laboratory (CENNS-10 and CENNS-750), one at Los Alamos (CCM), and a massive proposed one at Fermilab called PIP2-BD. Their goal was to see if these argon-based detectors could act as precision microscopes to measure the "weak mixing angle" (a fundamental setting in the universe's rulebook) and to hunt for sneaky, non-standard behaviors of neutrinos, like if they have a tiny magnetic personality or an effective electric size.

The simulations suggest that these argon detectors are incredibly promising tools. For the weak mixing angle, the authors find that the larger detectors, especially the proposed PIP2-BD, could measure this value with a precision that rivals or even beats current low-energy measurements. It's as if they are upgrading from a blurry pair of glasses to a high-definition camera, allowing scientists to see if the universe's rules change as the energy of the collision changes. Furthermore, the study shows these detectors could spot if neutrinos have a "magnetic moment" (acting like tiny magnets) or a "charge radius" (having a fuzzy electric edge). The simulations indicate that the PIP2-BD detector, if built with a 5% uncertainty in its measurements, could improve current limits on the neutrino's magnetic moment by nearly ten times, potentially reaching the range where new, exotic physics theories predict these properties might exist.

The paper also explores "Non-Standard Interactions" (NSIs), which are hypothetical ways neutrinos might talk to quarks (the building blocks of protons and neutrons) that aren't in the standard rulebook. The authors simulate how well these argon detectors could constrain these weird interactions. They find that the larger detectors can probe these interactions with a sensitivity that is competitive with, and sometimes better than, existing experiments. However, the authors are careful to note that these results are based on simulations assuming ideal conditions. They point out that the biggest hurdle isn't the size of the detector, but the "systematic uncertainties"—things like knowing exactly how many neutrinos are hitting the detector or how the detector responds to them. If these uncertainties can be kept low (around 5%), the results will be powerful; if they stay high (around 10%), the precision drops. Ultimately, the paper concludes that argon-based CEvNS experiments are a clean and versatile platform that could play a pivotal role in the next decade of neutrino physics, offering a clear window into the MeV scale of new physics.

Technical Summary: Prospects for Exploring Non-Standard Neutrino Properties with Argon-Based CEvNS Experiments

Problem Statement
Coherent elastic neutrino–nucleus scattering (CEvNS) serves as a critical framework for testing the Standard Model (SM) at low energies and searching for new physics. While the first observation of CEvNS was achieved in 2017, the field requires higher statistics and diverse target materials to perform precision measurements of electroweak parameters and constrain non-standard neutrino interactions (NSIs). Liquid argon (LAr) has emerged as a particularly attractive target due to its scalability, abundance, and the technological advancements driven by large-scale neutrino oscillation experiments (e.g., SBN and DUNE). However, a comprehensive evaluation of the specific physics reach of current and proposed argon-based detectors at stopped-pion sources regarding weak mixing angles, neutrino electromagnetic properties, and NSIs remains necessary to guide future experimental strategies.

Methodology
The authors evaluate the physics potential of four specific argon-based CEvNS configurations:

CENNS-10 and CENNS-750 at the Spallation Neutron Source (SNS), Oak Ridge National Laboratory (ORNL).
Coherent Captain Mills (CCM) at the Los Alamos Neutron Science Center (LANL).
PIP2-BD, a proposed 100-ton detector at Fermilab's Facility for Dark Matter Discovery (F2D2).

The analysis utilizes realistic neutrino fluxes from stopped-pion sources ( $\pi$ -DAR) and detector configurations corresponding to these facilities. The study employs the following technical approach:

Cross Section Formalism: The differential CEvNS cross section is calculated using the SM weak charge, incorporating various nuclear form factor models (Helm, Klein-Nystrand, and microscopic approaches like Hartree-Fock and EFT-SM). The Helm form factor is adopted as the baseline.
Event Rate Simulation: Projected event rates are computed for a three-year exposure (approx. 5000 hours/year). The analysis accounts for detector efficiency, energy resolution (modeled as a Gaussian), and a quenching factor to convert nuclear recoil energy to electron-equivalent energy.
Statistical Analysis: Sensitivities are evaluated using a $\chi^2$ minimization framework. The analysis assumes negligible background to estimate intrinsic sensitivity, while incorporating systematic uncertainties ( $\sigma_\eta$ ) of 10% (conservative, consistent with current COHERENT measurements) and 5% (optimistic, achievable with in-situ flux monitors).
Physics Targets: The study investigates deviations in total event rates and recoil spectra to constrain:
- The weak mixing angle ( $\sin^2 \theta_W$ ) at low momentum transfer.
- Neutrino electromagnetic properties: magnetic moment ( $\mu_\nu$ ) and effective charge radius ( $\langle r^2 \rangle_\nu$ ).
- Non-standard interactions (NSIs) with quarks, specifically flavor-conserving and flavor-changing neutral current parameters ( $\epsilon_{\alpha\beta}^{fV}$ ).

Key Contributions and Results

Weak Mixing Angle Precision: The study demonstrates that argon-based detectors can measure the weak mixing angle at momentum transfers well below the electroweak scale.
- The proposed PIP2-BD experiment, assuming a 5% systematic uncertainty, is projected to determine $\sin^2 \theta_W$ with a precision competitive with or superior to current low-energy determinations.
- CENNS-750 and CCM are also expected to reach comparable precision, enabling cross-checks across independent facilities.
- These measurements contribute to mapping the "running" of $\sin^2 \theta_W$ over several orders of magnitude in energy scale.
Neutrino Electromagnetic Properties:
- Magnetic Moment: The electromagnetic contribution enhances the scattering cross section at low recoil energies. The projected upper limits on the neutrino magnetic moment for PIP2-BD (with 5% systematics) improve upon current CEvNS bounds by nearly an order of magnitude, approaching regions predicted by various Beyond Standard Model (BSM) scenarios.
- Charge Radius: The analysis projects sensitivities to the neutrino charge radius at the level of $O(10^{-32}) \text{ cm}^2$ . These results are comparable to or slightly better than current limits from neutrino-electron scattering and coherent scattering on CsI, providing an independent cross-check of electroweak couplings.
Non-Standard Interactions (NSIs):
- The study evaluates constraints on flavor-diagonal ( $\epsilon_{ee}^{uV}, \epsilon_{ee}^{dV}, \epsilon_{\mu\mu}^{uV}, \epsilon_{\mu\mu}^{dV}$ ) and flavor-off-diagonal ( $\epsilon_{e\mu}^{uV}, \epsilon_{e\mu}^{dV}$ ) NSI parameters.
- Larger detectors (PIP2-BD, CENNS-750, CCM) show improved sensitivity compared to previous analyses of smaller detectors (CENNS-10), benefiting from increased target mass and reduced systematic uncertainties.
- The results indicate that combining CEvNS data with oscillation data can help resolve parameter degeneracies present in global fits, as CEvNS probes different linear combinations of NSI couplings weighted by nuclear charges.
Systematic Uncertainties: The analysis highlights that for high-statistics configurations like PIP2-BD, the sensitivity is currently systematics-dominated. Future improvements will depend primarily on reducing uncertainties in flux normalization, detector response, and nuclear modeling.

Significance and Claims
The paper asserts that argon-based CEvNS experiments represent a "clean and versatile platform" for precision exploration of non-standard neutrino properties. The authors claim that:

These experiments will enable stringent tests of the running of the weak mixing angle at low momentum transfers, a regime where the SM prediction is less precisely tested.
They offer a discovery channel for new physics at the MeV scale, specifically through the detection of neutrino magnetic moments and charge radii, and through constraints on NSIs.
The combination of existing facilities (SNS, LANL) and future proposals (F2D2) creates a global program capable of delivering unprecedented statistics and precision.
The results provide critical input for global fits, helping to break degeneracies in NSI parameter space that cannot be resolved by oscillation experiments alone.

The authors conclude that forthcoming argon-based measurements will play a pivotal role in precision neutrino physics, offering an incisive window into new physics at the MeV scale.

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