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arxiv: 2604.05746 · v1 · submitted 2026-04-07 · ✦ hep-ex

Reactor Antineutrino Oscillations and Geoneutrinos in SNO+

William Parker This is my paper

Pith reviewed 2026-05-10 18:42 UTC · model grok-4.3

classification ✦ hep-ex
keywords neutrino oscillationsgeoneutrinosreactor antineutrinosSNO+Δm²₂₁Western Hemisphereliquid scintillator
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The pith

SNO+ measures the neutrino oscillation parameter Δm²₂₁ as (7.93 +0.21 -0.24) × 10^{-5} eV² from reactor antineutrino data.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper reports results from the SNO+ liquid-scintillator detector at SNOLAB using reactor antineutrinos produced at baselines of 240 to 350 km. A spectral fit extracts the value of Δm²₂₁ after 685 days of livetime while simultaneously determining the mixing angle θ₁₂, the reactor flux, and background rates. The measured Δm²₂₁ agrees with earlier results from KamLAND and JUNO. The same dataset produces the first geoneutrino flux measurement in the Western Hemisphere. These numbers test neutrino oscillation models and geological predictions for Earth's radioactive heat sources.

Core claim

Using data collected between May 2022 and July 2025, corresponding to a livetime of 685 days, a value of Δm²₂₁ = (7.93^{+0.21}_{-0.24}) × 10^{-5} eV² is obtained. This result is compatible with other long-baseline reactor antineutrino measurements by KamLAND and JUNO. SNO+ has also made the first measurement of the geoneutrino flux in the Western Hemisphere, measuring 49^{+13}_{-12} TNU, in agreement with predictions from geological models.

What carries the argument

A simultaneous spectral fit of the antineutrino energy spectrum that varies Δm²₂₁, θ₁₂, reactor flux normalization, background rates, and detector systematics.

If this is right

  • The measured Δm²₂₁ can be combined with KamLAND and JUNO results to tighten global constraints on solar neutrino parameters.
  • The geoneutrino flux provides an independent check on models of uranium and thorium distribution in the Canadian crust and mantle.
  • Future SNO+ data will allow a more precise extraction of θ₁₂ at the same baseline range.
  • The analysis method shows that a single detector can separate oscillation signals from geoneutrino signals in the same dataset.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • An independent measurement at this baseline range can help test whether current global fits of Δm²₂₁ are consistent across experiments.
  • Repeated geoneutrino measurements at different sites could eventually allow tomography of heat-producing elements inside the Earth.
  • Improved reactor-background subtraction techniques developed here may benefit other liquid-scintillator detectors placed near nuclear plants.

Load-bearing premise

The fit assumes reactor antineutrino flux, background rates, and detector response are accurately modeled and can be varied together without large bias from missing correlations or incomplete background knowledge.

What would settle it

A new long-baseline reactor experiment or extended SNO+ dataset returning a central value for Δm²₂₁ lying well outside the reported 1-sigma interval, or a geoneutrino rate far from 49 TNU.

Figures

Figures reproduced from arXiv: 2604.05746 by William Parker.

Figure 1
Figure 1. Figure 1: Best-fit energy distribution for the fit with PDG constraints on oscillation parameters and [PITH_FULL_IMAGE:figures/full_fig_p005_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: 2-D log-likelihood contours of ∆m2 21 vs. sin2 θ12, with 1-D log-likelihood profiles. Results are shown for this analysis, as well as results from KamLAND [14] and combined solar measurements [15], along with the combined fit of SNO+ and the PDG 2025 global results [13]. 0 5 - 2 l o g ( L ) KamLAND Solar SNO+ Combined 0.2 0.3 0.4 0.5 0.6 sin 2 12 5.5 6.0 6.5 7.0 7.5 8.0 8.5 m 2 2 1 [ 1 0 5 e V 2 ] Best Fit… view at source ↗
read the original abstract

SNO+ is a multipurpose liquid-scintillator neutrino detector located 2 km underground at SNOLAB, Canada. Three large nuclear reactors at baselines of 240-350 km allow a precise measurement of the neutrino oscillation parameter $\Delta m^2_{21}$ and, to a lesser extent, $\theta_{12}$. A spectral analysis is performed, simultaneously fitting $\Delta m^2_{21}$, $\theta_{12}$, the reactor antineutrino flux, background rates, and associated systematics. Using data collected between May 2022 and July 2025, corresponding to a livetime of 685 days, a value of $\Delta m^2_{21} = (7.93^{+0.21}_{-0.24}) \times 10^{-5}$ eV$^2$ is obtained. This result is compatible with other long-baseline reactor antineutrino measurements by KamLAND and JUNO. SNO+ has also made the first measurement of the geoneutrino flux in the Western Hemisphere, measuring $49^{+13}_{-12}$ TNU, in agreement with predictions from geological models.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

2 major / 2 minor

Summary. The manuscript reports results from the SNO+ liquid-scintillator detector on reactor antineutrino oscillations and geoneutrinos. Using 685 days of livetime collected between May 2022 and July 2025, a joint spectral fit simultaneously extracts Δm²₂₁ = (7.93^{+0.21}_{-0.24}) × 10^{-5} eV² along with θ₁₂, reactor flux normalization, background rates, and detector systematics. The result is stated to be compatible with KamLAND and JUNO. The paper also presents the first geoneutrino flux measurement in the Western Hemisphere, 49^{+13}_{-12} TNU, in agreement with geological models.

Significance. If the spectral fit is shown to be robust against the floated parameters, this constitutes an independent long-baseline reactor measurement of the solar oscillation parameters at baselines of 240-350 km, adding a new data point to the global fit. The geoneutrino result supplies the first constraint from the Western Hemisphere, which can be combined with KamLAND data to test geological models of radiogenic heat production. The simultaneous fit approach and use of a single detector for both signals are standard strengths of the analysis.

major comments (2)
  1. [§4 (Spectral Analysis and Fit)] §4 (Spectral Analysis and Fit): The central claims rest on a single joint fit that floats Δm²₂₁, θ₁₂, reactor normalization, multiple background rates, and systematics. The manuscript must provide the post-fit correlation coefficients (or full covariance matrix) between Δm²₂₁ and the background normalizations, as well as the parameterization of reactor spectrum uncertainties. Without these, it is impossible to verify that mismodeling in the prompt-energy spectra is not absorbed into the oscillation dip or the low-energy geoneutrino excess, as raised by the simultaneous-fit concern.
  2. [§5 (Geoneutrino Results)] §5 (Geoneutrino Results): The geoneutrino flux of 49^{+13}_{-12} TNU is extracted from the same fit. The paper should include explicit validation (e.g., fit stability under variations of the reactor spectrum model or control-sample constraints on the dominant backgrounds) to demonstrate that the low-energy excess is not biased by incomplete background knowledge or unaccounted correlations with the reactor component.
minor comments (2)
  1. [Abstract] The abstract states the livetime but does not specify the prompt-energy range or fiducial volume used in the fit; these details should be added for reproducibility.
  2. Figure captions for the spectral fit plots should explicitly state the pull terms or nuisance parameters that were varied and the resulting χ²/dof.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the careful and constructive review of our manuscript. We address each major comment below and have revised the paper to provide the requested information on fit correlations, uncertainty parameterizations, and validation studies.

read point-by-point responses

  1. Referee: §4 (Spectral Analysis and Fit): The central claims rest on a single joint fit that floats Δm²₂₁, θ₁₂, reactor normalization, multiple background rates, and systematics. The manuscript must provide the post-fit correlation coefficients (or full covariance matrix) between Δm²₂₁ and the background normalizations, as well as the parameterization of reactor spectrum uncertainties. Without these, it is impossible to verify that mismodeling in the prompt-energy spectra is not absorbed into the oscillation dip or the low-energy geoneutrino excess, as raised by the simultaneous-fit concern.

    Authors: We agree that the post-fit correlations and reactor spectrum uncertainty parameterization should be explicitly shown to allow independent verification of the fit robustness. In the revised manuscript we have added a new table in Section 4 that reports the correlation coefficients between Δm²₂₁ and the principal floated background normalizations, together with a concise description of the reactor spectrum uncertainty parameterization (including the energy-dependent shape uncertainties and their propagation). These additions confirm that the correlations remain modest and do not indicate that background mismodeling is being absorbed into the oscillation parameters or the geoneutrino signal. revision: yes

  2. Referee: §5 (Geoneutrino Results): The geoneutrino flux of 49^{+13}_{-12} TNU is extracted from the same fit. The paper should include explicit validation (e.g., fit stability under variations of the reactor spectrum model or control-sample constraints on the dominant backgrounds) to demonstrate that the low-energy excess is not biased by incomplete background knowledge or unaccounted correlations with the reactor component.

    Authors: We have performed the requested validation studies. Fits were repeated with the reactor spectrum model varied within its full uncertainty envelope and with additional constraints derived from control samples on the dominant backgrounds. The extracted geoneutrino flux remains stable, with shifts well within the quoted uncertainties. A new paragraph and supplementary figure have been added to Section 5 documenting these checks and demonstrating that the low-energy excess is not biased by the effects raised by the referee. revision: yes

Circularity Check

0 steps flagged

Direct spectral fit to experimental data; no derivation reduces to self-definition or fitted inputs

full rationale

The paper reports an empirical measurement obtained by performing a simultaneous spectral fit of oscillation parameters (Δm²₂₁, θ₁₂), reactor flux normalization, background rates, and detector systematics to 685 days of SNO+ data. The quoted values of Δm²₂₁ = (7.93^{+0.21}_{-0.24}) × 10^{-5} eV² and geoneutrino flux 49^{+13}_{-12} TNU are direct outputs of this fit to observed prompt-energy spectra; they are not defined in terms of themselves, nor do any equations or self-citations make the result tautological by construction. No load-bearing step invokes a uniqueness theorem, ansatz smuggled via prior work, or renaming of a known result. The analysis is self-contained against external benchmarks (KamLAND, JUNO, geological models) and contains no circular reduction.

Axiom & Free-Parameter Ledger

4 free parameters · 2 axioms · 0 invented entities

This is an experimental measurement paper relying on established neutrino physics and geological models; the fitted parameters are the outputs rather than inputs.

free parameters (4)
  • Δm²₂₁
    Fitted from spectral analysis of reactor antineutrino data.
  • θ12
    Fitted to a lesser extent from the same data.
  • reactor antineutrino flux
    Fitted simultaneously with oscillation parameters.
  • background rates
    Fitted simultaneously with signal parameters.
axioms (2)
  • standard math Standard three-flavor neutrino oscillation framework
    Used for fitting Δm²₂₁ and θ12 from reactor antineutrino spectrum.
  • domain assumption Geoneutrino production models from geological predictions
    Used to compare the measured flux of 49 TNU.

pith-pipeline@v0.9.0 · 5493 in / 1435 out tokens · 55304 ms · 2026-05-10T18:42:49.636113+00:00 · methodology

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Reference graph

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