[Paper Review] Bounds on new physics with data of the Dresden-II reactor experiment and COHERENT

Pilar Coloma, Ivan Esteban+4 more|arXiv (Cornell University)|Feb 22, 2022

Neutrino Physics Research93 references53 citations

TL;DR

This paper presents the first constraints on new physics using data from the Dresden-II reactor experiment, which reported the first observation of coherent elastic neutrino-nucleus scattering (CEνNS) with reactor antineutrinos. By combining Dresden-II data with COHERENT data from spallation neutron sources, the study strengthens bounds on neutrino non-standard interactions, magnetic moments, and light scalar/vector mediators—particularly highlighting the enhanced sensitivity from elastic scattering off electrons, which improves constraints by up to a factor of 5 for light vector mediators below 20 MeV mass.

ABSTRACT

Coherent elastic neutrino-nucleus scattering was first experimentally established five years ago by the COHERENT experiment using neutrinos from the spallation neutron source at Oak Ridge National Laboratory. The first evidence of observation of coherent elastic neutrino-nucleus scattering with reactor antineutrinos has now been reported by the Dresden-II reactor experiment, using a germanium detector. In this paper, we present constraints on a variety of beyond the Standard Model scenarios using the new Dresden-II data. In particular, we explore the constraints imposed on neutrino non-standard interactions, neutrino magnetic moments, and several models with light scalar or light vector mediators. We also quantify the impact of their combination with COHERENT (CsI and Ar) data. In doing so, we highlight the synergies between spallation neutron source and nuclear reactor experiments regarding beyond the Standard Model searches, as well as the advantages of combining data obtained with different nuclear targets. We also study the possible signal from beyond the Standard Model scenarios due to elastic scattering off electrons (which would pass selection cuts of the COHERENT CsI and the Dresden-II experiments) and find more stringent constraints in certain parts of the parameter space than those obtained considering coherent elastic neutrino-nucleus scattering.

Motivation & Objective

• To derive new constraints on beyond-the-Standard-Model (BSM) physics using the first observation of coherent elastic neutrino-nucleus scattering (CEνNS) with reactor antineutrinos from the Dresden-II experiment.
• To quantify the synergistic potential between reactor and spallation neutron source experiments (e.g., COHERENT) in probing BSM scenarios through CEνNS and electron scattering.
• To assess the impact of elastic scattering off electrons—previously neglected in BSM analyses—on improving sensitivity in models with light mediators or magnetic moments.
• To compare the sensitivity of different nuclear targets (Ge, CsI, Ar) in constraining flavor-dependent and universal BSM interactions.
• To evaluate the reach of low-momentum-transfer experiments in probing light new physics, especially in scenarios where CEνNS is subdominant to electron scattering.

Proposed method

• Used the newly released high-exposure data from the Dresden-II reactor experiment, which reports a strong preference for CEνNS over background in germanium detectors.
• Combined Dresden-II data with COHERENT data from CsI and argon detectors at the Spallation Neutron Source, leveraging differences in neutrino flavor composition and target nuclei.
• Constructed event rate predictions for CEνNS and elastic scattering off electrons (ES) in various BSM models: non-standard neutrino interactions (NSI), neutrino magnetic moments, and light scalar/vector mediators.
• Applied Bayesian statistical analysis to compare signal hypotheses (BSM + SM) against the background-only hypothesis, computing Bayes factors and posterior distributions.
• Incorporated realistic detector effects including quenching factors, energy resolution, and electron binding energy corrections (via effective Zeff) for Ge, CsI, and Ar.
• Evaluated the sensitivity of each experiment and their combination to different BSM parameters, especially focusing on low-momentum-transfer regimes where ES can dominate.

Experimental results

Research questions

• RQ1 How do the new data from the Dresden-II reactor experiment improve constraints on neutrino non-standard interactions (NSI) compared to previous limits?
• RQ2 To what extent does including elastic scattering off electrons enhance sensitivity to light vector and scalar mediators in CEνNS experiments?
• RQ3 What is the synergistic gain in sensitivity when combining COHERENT (SNS) and Dresden-II (reactor) data, especially for flavor-dependent BSM interactions?
• RQ4 How do the bounds on neutrino magnetic moments compare between COHERENT and Dresden-II, and which experiment is more sensitive for different neutrino flavors?
• RQ5 In which regions of parameter space does electron scattering dominate over CEνNS, and how does this affect the reach for light mediators below 100 MeV?

Key findings

• The inclusion of electron scattering (ES) in the analysis improves constraints on light vector mediators (B−L and universal models) by at least a factor of 5 for mediator masses below 20 MeV, compared to CEνNS-only bounds.
• For COHERENT CsI data, ES contributes significantly to the signal and leads to stronger bounds than CEνNS alone in the low-mass vector mediator regime.
• Dresden-II data outperform COHERENT in constraining neutrino magnetic moments (except for muon neutrino magnetic moments, which are only accessible via COHERENT's mixed-flavor flux).
• The combination of COHERENT (CsI, Ar) and Dresden-II (Ge) data breaks degeneracies in non-standard interaction (NSI) parameters, particularly improving constraints on electron-flavor NSI parameters.
• For light scalar mediators and neutrino magnetic moments, CEνNS remains the dominant signal in the Dresden-II energy range, but ES becomes competitive at higher energies.
• Extending the reconstructed energy range in future analyses could significantly enhance the sensitivity of the Dresden-II experiment to BSM scenarios involving light vector mediators.