Global Fit of KamLAND Data and the Daya Bay Antineutrino Energy Spectrum

arxiv: 2605.16915 · v1 · pith:Q3HKNL34new · submitted 2026-05-16 · ✦ hep-ex

Global Fit of KamLAND Data and the Daya Bay Antineutrino Energy Spectrum

Guihong Huang This is my paper

Pith reviewed 2026-05-19 19:03 UTC · model grok-4.3

classification ✦ hep-ex

keywords reactor antineutrino spectrumneutrino oscillationsKamLANDDaya Baysolar neutrino parametersJUNOglobal fit

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The pith

Substituting Daya Bay's measured antineutrino spectra for the Huber-Müller model in a KamLAND analysis lowers the best-fit Δm²₂₁ and improves agreement with JUNO.

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

The paper tests whether the known mismatch between predicted and measured reactor antineutrino spectra affects extraction of solar neutrino oscillation parameters from KamLAND. It builds a global fit that uses Daya Bay's direct measurements of the 235U and 239Pu fission spectra rather than a theoretical model. Applying this to KamLAND data produces a small downward shift in the best-fit Δm²₂₁ to 7.50^{+0.19}_{-0.18}×10^{-5} eV² along with a trend toward lower tan²θ₁₂. A sympathetic reader would care because spectrum modeling differences may explain the tension between KamLAND and the newer JUNO measurement.

Core claim

The paper claims that replacing the Huber-Müller model with Daya Bay measured antineutrino spectra in a combined analysis with KamLAND public data decreases the best-fit value of Δm²₂₁ from 7.53^{+0.17}_{-0.16}×10^{-5} eV² to 7.50^{+0.19}_{-0.18}×10^{-5} eV² while tan²θ₁₂ trends downward. This result shows better agreement with the latest JUNO measurement and indicates that differences in predicted reactor antineutrino spectra may be an important cause of the tension between the experiments.

What carries the argument

A global analysis framework that combines KamLAND data with Daya Bay's independently measured 235U and 239Pu fission antineutrino spectra while remaining weakly dependent on the overall reactor flux model.

Load-bearing premise

The Daya Bay measured 235U and 239Pu fission antineutrino spectra can be directly substituted into the KamLAND analysis with only weak dependence on the overall reactor flux model and without large additional detector-specific corrections.

What would settle it

Repeating the fit with an independent reactor antineutrino spectrum measurement that matches the Huber-Müller prediction exactly and lacks the 5 MeV feature would remove the observed shift in the oscillation parameters.

Figures

Figures reproduced from arXiv: 2605.16915 by Guihong Huang.

**Figure 2.** Figure 2: Fit results for the best-fit oscillation spectrum. The oscillated spectral [PITH_FULL_IMAGE:figures/full_fig_p002_2.png] view at source ↗

**Figure 3.** Figure 3: Allowed regions at 95%, 99%, and 99.73% confidence levels in the (tan2 θ12, ∆m 2 21) plane. The filled colored areas are the reproduction results of this work, and the contours are the official results. for 238U and 241Pu in the KamLAND χ 2 term is set to 10%. For safety, we keep the expected no-oscillation event counts unchanged. The Daya Bay inputs include the unfolded spectra of 235U and 239Pu, their co… view at source ↗

**Figure 5.** Figure 5: Projections of ∆χ 2 onto each oscillation parameter in the constrained θ13 case. After including the Daya Bay measured antineutrino spectra, the bestfit central values of ∆m 2 21 and tan2 θ12 decrease systematically. 4. Conclusion Based on the KamLAND 2013 long-baseline reactor neutrino oscillation data and the Daya Bay 2019 short-baseline antineutrino spectra of 235U and 239Pu, we have constructed a det… view at source ↗

**Figure 4.** Figure 4: Projections of ∆χ 2 onto each oscillation parameter in the free θ13 case. After including the Daya Bay measured antineutrino spectra, the best-fit central values of ∆m 2 21 and tan2 θ12 decrease systematically. ]2 [eV 2 ∆m21 65 70 75 80 85 -6 ×10 2 χ ∆ 0 1 2 3 4 5 6 7 8 9 10 H.M. DYB_2017_Total DYB_2019_U235+Pu239 constrained 13 θ 12 θ 2 tan 0 0.2 0.4 0.6 0.8 1 2 χ ∆ 0 1 2 3 4 5 6 7 8 9 10 [PITH_FULL_IMAG… view at source ↗

read the original abstract

Recently, the JUNO experiment published its measurement of the solar neutrino oscillation parameters $\Delta m^2_{21}$ and $\sin^2\theta_{12}$ based on 59 days of data, with central values differing by $0.2\sigma$ from those released by the KamLAND experiment in 2013. Meanwhile, short-baseline reactor neutrino oscillation experiments such as Daya Bay, RENO, and Double Chooz have observed significant deviations between the measured antineutrino spectrum and the Huber-M\"{u}ller model prediction around 5~MeV. To further investigate the impact of these deviations on the measurement of reactor neutrino oscillation parameters, we construct a global analysis framework that is weakly dependent on the reactor antineutrino flux model. This framework is based on the independently measured $^{235}\mathrm{U}$ and $^{239}\mathrm{Pu}$ fission antineutrino spectra from the Daya Bay experiment, combined with the public data from KamLAND. First, using the Huber-M\"{u}ller model, we successfully reproduce the KamLAND 2013 results to within $0.1\sigma$. Then, replacing the Huber-M\"{u}ller model with the Daya Bay measured antineutrino spectra in a combined analysis, we find that the best-fit value of the mass-squared difference $\Delta m^2_{21}$ decreases from $7.53^{+0.17}_{-0.16}\times10^{-5}\,\mathrm{eV^2}$ to $7.50^{+0.19}_{-0.18}\times10^{-5}\,\mathrm{eV^2}$, while the best-fit value of the mixing angle $\tan^2\theta_{12}$ also shows a decreasing trend. This result is in better agreement with the latest JUNO measurement, suggesting that differences in the predicted reactor antineutrino spectra may be an important cause of the tension between the two experiments.

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.

Desk Editor's Note private letter to a colleague

Swapping Daya Bay spectra into the KamLAND fit produces a small downward shift in Delta m squared 21 that edges closer to JUNO but stays well inside the errors.

read the letter

The main takeaway is that this paper tests whether the reactor spectrum anomaly seen at Daya Bay can explain part of the mild tension between KamLAND and JUNO solar parameters. They recover the original 2013 KamLAND result to 0.1 sigma with the standard Huber-Müller model, then substitute the measured 235U and 239Pu spectra from Daya Bay and see Delta m squared 21 move from 7.53 to 7.50 times 10 to the minus 5, with tan squared theta 12 trending lower as well. The new central values sit a bit closer to JUNO's numbers. That specific numerical outcome from the substitution is new and the framework is set up to depend only weakly on the overall flux normalization, which is a sensible choice. They use public KamLAND data and independent Daya Bay measurements, so the exercise is straightforward to check. The internal consistency looks fine for what is shown. The soft spot is the handling of detector differences. KamLAND and Daya Bay have different resolutions, quenching, and calibration, and the abstract does not show explicit propagation of those effects or tests for bin migration around the 5 MeV region. The reported shift is smaller than the uncertainty, so any residual mismatch could matter at the level they care about. A full paper should include those checks to make the claim robust. This is useful for people who follow reactor neutrino global fits and the solar parameter comparison. A reader working on oscillation analyses or preparing for JUNO data would find it relevant. It deserves a serious referee because the question is well-posed and the method is transparent, even if the size of the effect is modest. I would send it to peer review and ask for more detail on the inter-experiment systematics and sensitivity tests.

Referee Report

1 major / 1 minor

Summary. The paper constructs a global fit framework for KamLAND reactor antineutrino oscillation data that substitutes the Daya Bay experiment's directly measured 235U and 239Pu fission antineutrino spectra for the Huber-Müller model prediction. It first reproduces the KamLAND 2013 best-fit values of Δm²₂₁ = 7.53^{+0.17}_{-0.16}×10^{-5} eV² and tan²θ₁₂ to within 0.1σ using the standard model, then reports that the substitution shifts the best-fit Δm²₂₁ downward to 7.50^{+0.19}_{-0.18}×10^{-5} eV² with a decreasing trend in tan²θ₁₂, improving agreement with the recent JUNO result. The framework is presented as having only weak dependence on the overall reactor flux normalization.

Significance. If the central substitution is valid, the result indicates that measured spectral deviations around 5 MeV in short-baseline reactor experiments can partially account for the mild tension between KamLAND and JUNO determinations of the solar oscillation parameters. The explicit reproduction of the 2013 KamLAND result to 0.1σ provides a useful internal consistency check on the analysis pipeline. The approach of using experimentally unfolded spectra rather than a theoretical model is a constructive step toward reducing model dependence in reactor neutrino oscillation fits.

major comments (1)

[abstract / global analysis framework] Abstract and global analysis framework paragraph: the central claim that Daya Bay measured spectra can be directly substituted into the KamLAND prediction with only weak overall flux dependence requires that residual differences in energy resolution (~6-8% at 1 MeV), quenching, and bin migration between the two detectors produce shape distortions smaller than the reported 0.03×10^{-5} eV² shift in Δm²₂₁. No explicit quantification or propagation of these inter-experiment effects is shown, yet they are load-bearing for interpreting the parameter shift as arising solely from the 5 MeV spectral feature.

minor comments (1)

[abstract] The abstract states reproduction 'to within 0.1σ' but does not specify whether this refers to the central value, the uncertainty, or the full covariance; a brief clarification in the methods section would aid reproducibility.

Simulated Author's Rebuttal

1 responses · 0 unresolved

We thank the referee for the constructive review and for highlighting the value of the internal consistency check with the 2013 KamLAND result. The major comment raises an important point about inter-experiment detector effects that we address below. We believe the substitution remains valid but agree that explicit quantification will strengthen the manuscript.

read point-by-point responses

Referee: [abstract / global analysis framework] Abstract and global analysis framework paragraph: the central claim that Daya Bay measured spectra can be directly substituted into the KamLAND prediction with only weak overall flux dependence requires that residual differences in energy resolution (~6-8% at 1 MeV), quenching, and bin migration between the two detectors produce shape distortions smaller than the reported 0.03×10^{-5} eV² shift in Δm²₂₁. No explicit quantification or propagation of these inter-experiment effects is shown, yet they are load-bearing for interpreting the parameter shift as arising solely from the 5 MeV spectral feature.

Authors: We agree that a quantitative assessment of residual differences in energy resolution, quenching, and bin migration is necessary to fully support the interpretation that the observed 0.03×10^{-5} eV² shift originates primarily from the 5 MeV spectral feature rather than detector-response mismatches. The Daya Bay spectra used are the unfolded true-energy spectra published by the collaboration, which already incorporate their own detector response. When these are folded with the KamLAND response matrix in our framework, the dominant effect is the shape difference around 5 MeV. To address the referee’s concern, we will add a new subsection in the global analysis framework section that propagates these effects via Monte Carlo simulation of both detectors’ responses. Preliminary checks indicate that the induced shape distortion in the 2–8 MeV range is at the sub-percent level, well below the statistical sensitivity of the KamLAND data set that drives the 0.03×10^{-5} eV² shift. We will include the resulting uncertainty band on the best-fit parameters to demonstrate that the central shift remains robust. revision: yes

Circularity Check

0 steps flagged

Independent inputs produce non-circular parameter shift

full rationale

The paper constructs a global fit by taking the publicly released KamLAND event spectrum and substituting the independently unfolded Daya Bay 235U/239Pu fission spectra (measured at a different detector with its own resolution and efficiency) in place of the Huber-Müller model. The reproduction of the 2013 KamLAND result to 0.1σ with the standard model first verifies the analysis chain; the subsequent shift in Δm²₂₁ and tan²θ₁₂ is then a direct numerical output of that same likelihood function evaluated on the new spectral shape. No equation defines a fitted parameter in terms of the target oscillation parameters, no self-citation supplies a uniqueness theorem, and no ansatz is smuggled through prior work by the same author. The derivation therefore remains self-contained against external benchmarks.

Axiom & Free-Parameter Ledger

2 free parameters · 1 axioms · 0 invented entities

The central claim rests on the standard three-flavor neutrino oscillation probability formula and the assumption that Daya Bay's measured spectra apply directly to KamLAND without major additional corrections.

free parameters (2)

Δm²₂₁
Fitted parameter in the global chi-squared analysis of KamLAND data with substituted spectra.
tan²θ₁₂
Fitted mixing parameter showing the reported decreasing trend.

axioms (1)

domain assumption Reactor antineutrino oscillation is described by the standard three-flavor vacuum oscillation formula.
Invoked in the global fit framework described in the abstract.

pith-pipeline@v0.9.0 · 5888 in / 1550 out tokens · 56706 ms · 2026-05-19T19:03:20.019014+00:00 · methodology

discussion (0)

Lean theorems connected to this paper

Citations machine-checked in the Pith Canon. Every link opens the source theorem in the public Lean library.

IndisputableMonolith/Foundation/RealityFromDistinction.lean reality_from_one_distinction unclear

?

unclear
Relation between the paper passage and the cited Recognition theorem.

replacing the Huber-Müller model with the Daya Bay measured antineutrino spectra in a combined analysis
IndisputableMonolith/Cost/FunctionalEquation.lean washburn_uniqueness_aczel unclear

?

unclear
Relation between the paper passage and the cited Recognition theorem.

global analysis framework that is weakly dependent on the reactor antineutrino flux model

What do these tags mean?

matches: The paper's claim is directly supported by a theorem in the formal canon.
supports: The theorem supports part of the paper's argument, but the paper may add assumptions or extra steps.
extends: The paper goes beyond the formal theorem; the theorem is a base layer rather than the whole result.
uses: The paper appears to rely on the theorem as machinery.
contradicts: The paper's claim conflicts with a theorem or certificate in the canon.
unclear: Pith found a possible connection, but the passage is too broad, indirect, or ambiguous to say the theorem truly supports the claim.

Reference graph

Works this paper leans on

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work page doi:10.1103/physrevlett.116.211801 2016

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work page doi:10.1088/1674- 2017

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work page doi:10.1103/physrevlett.123.111801 2019

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work page doi:10.1088/1674-1137/abfc38 2021

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Measurement of the Electron Antineu- trino Oscillation with 1958 Days of Operation at Daya Bay

Daya Bay, "Measurement of the Electron Antineu- trino Oscillation with 1958 Days of Operation at Daya Bay", Phys. Rev. Lett.121(2018) no.24, 241805. doi:10.1103/PhysRevLett.121.241805 6

work page doi:10.1103/physrevlett.121.241805 1958