REVIEW
First Measurement of Solar Neutrinos through Elastic Neutrino-Electron Scattering at the keV Scale
High Energy Physics - Experiment · Submitted 29 Aug 2026 · 81 references
Pith's verdict: A plausible, carefully framed first measurement of pp solar neutrinos at keV-scale recoil energies from XENONnT — worth a serious referee, even though the copy I saw only let me verify the abstract, not the background model.
T0 · AI review
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Referee report
The paper
The paper claims
XENONnT measured solar pp neutrinos via elastic neutrino-electron scattering at keV-scale energies, rejecting background-only at 5.0 sigma and reporting a flux of (10.2 ± 2.0) × 10^10 cm^-2 s^-1.
The reading
What carries the argument
The central mechanism is elastic neutrino-electron scattering in liquid xenon: a solar neutrino hits an electron and the detector records the electron's recoil as both scintillation light and ionization. The observable signal is the recoil spectrum between 1 and 140 keV, and the pp neutrinos—the low-energy neutrinos from the first step of the Sun's proton-proton fusion chain—contribute a smooth, steeply falling spectrum at the lower end. The measurement rests on a profile-likelihood fit of 2.46 tonne-years of data from a liquid-xenon time projection chamber, with background components that include electronic noise, surface contamination, and radiogenic sources. The signal template is fixed by the standard model, so the fit's job is to separate that known shape from the modeled backgrounds. That combination of a low threshold and a precisely predicted spectrum is what turns the dark-matter detector into a solar-neutrino spectrometer.
Extended reading notes
Core claim
The paper's central claim is that the 1–140 keV electron-recoil spectrum recorded by XENONnT contains a component from solar neutrinos scattering off electrons, dominated by pp neutrinos. Fitting the spectrum with a background model and the standard-model neutrino-electron scattering rate excludes the background-only hypothesis at $5.0\sigma$ and yields a pp flux of $(10.2 \pm 2.0)\times 10^{10}\ \mathrm{cm}^{-2}\ \mathrm{s}^{-1}$. Because the analysis starts at 1 keV of recoil energy, it is sensitive to neutrino energies as low as 17 keV, the lowest threshold achieved by any neutrino detection. The paper also reports that the flux is larger than Borexino's measurement but compatible with it at $1.9\sigma$, and that this is the first demonstration of low-energy solar-neutrino detection via neutrino-electron scattering in a dark-matter detector.
Load-bearing premise
The load-bearing premise is that every non-neutrino source of events in the 1–140 keV electron-recoil window is understood well enough to model, so that the excess left after background subtraction is entirely solar-neutrino scattering.
Editorial extensions
If this is right
- Solar neutrinos can now be measured down to 17 keV, the lowest neutrino energy threshold of any detection technique to date.
- Liquid-xenon time projection chambers are shown to be viable instruments for solar-neutrino physics, not only for dark-matter searches.
- Together with the recent observation of $^8$B solar neutrinos through coherent elastic neutrino-nucleus scattering in XENONnT, this result supports a next-generation liquid-xenon observatory that does both dark-matter and neutrino physics.
- The pp flux measurement provides a new low-energy comparison point with solar-model predictions and with Borexino's independently measured flux.
Reading between the lines
- If the excess is real, additional exposure should reveal the 7Be and pep solar-neutrino components in the same recoil window; their known relative intensities would provide a sharp check of the solar model and of the detector's energy response.
- The measured flux sits roughly 2 sigma above Borexino; whether that shift is a background artifact or a hint of new low-energy neutrino interactions will be settled by independent detectors or by the same detector with more exposure.
- This measurement also quantifies an irreducible background for future low-threshold dark-matter searches in xenon: solar neutrino-electron scattering will eventually limit how low an electron-recoil search can go.
Original abstract
We report on the first measurement of low-energy solar neutrinos through elastic neutrino-electron scattering in a dark matter experiment, establishing the lowest energy threshold for any neutrino detection to date. The measurement utilizes data from the first two science runs of XENONnT, corresponding to an exposure of 2.46 t $\cdot$ y, and covers electron recoil energies between 1 keV and 140 keV, providing sensitivity to solar neutrinos with energies down to 17 keV. We reject the background-only hypothesis with a statistical significance of $5.0\sigma$ and measure a solar $pp$ neutrino flux of $(10.2 \pm 2.0) \times 10^{10}$ cm$^{-2}$ s$^{-1}$. The result is larger, but statistically consistent with the previous measurement by Borexino at $1.9\sigma$. Together with recent observations of coherent elastic neutrino-nucleus scattering of $^8$B solar neutrinos in XENONnT and other liquid-xenon time projection chambers, these results demonstrate the growing potential of liquid xenon detectors for neutrino physics down to the keV-scale and represent an important milestone towards a next-generation multipurpose observatory.
The compiled record
The paper's own sentences, arranged, kept beside the review and separate from it. Each label is drawn from a closed vocabulary; the number beside it is the probability the classifier gave that label. Numbers in the tables are the authors', checked by code. No sentence in this record was written by a model.
The abstract, sentence by sentence
We report on the first measurement of low-energy solar neutrinos through elastic neutrino-electron scattering in a dark matter experiment, establishing the lowest energy threshold for any neutrino detection to date. The measurement utilizes data from the first two science runs of XENONnT, corresponding to an exposure of 2.46 t $\cdot$ y, and covers electron recoil energies between 1 keV and 140 keV, providing sensitivity to solar neutrinos with energies down to 17 keV. We reject the background-only hypothesis with a statistical significance of $5.0\sigma$ and measure a solar $pp$ neutrino flux of $(10.2 \pm 2.0) \times 10^{10}$ cm$^{-2}$ s$^{-1}$. The result is larger, but statistically consistent with the previous measurement by Borexino at $1.9\sigma$. Together with recent observations of coherent elastic neutrino-nucleus scattering of $^8$B solar neutrinos in XENONnT and other liquid-xenon time projection chambers, these results demonstrate the growing potential of liquid xenon detectors for neutrino physics down to the keV-scale and represent an important milestone towards a next-generation multipurpose observatory.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | We report on the first measurement of low-energy solar neutrinos through elastic neutrino-electron scattering in a dark matter experiment, establishing the lowest energy threshold for any neutrino detection to date. | contribution 0.94 | 0.97 | 0.87 | asserted 1.00 |
| s1 | The measurement utilizes data from the first two science runs of XENONnT, corresponding to an exposure of 2.46 t $\cdot$ y, and covers electron recoil energies between 1 keV and 140 keV, providing sensitivity to solar neutrinos with energies down to 17 keV. | method 1.00 | 0.94 | 0.08 | asserted 1.00 |
| s2 | We reject the background-only hypothesis with a statistical significance of $5.0\sigma$ and measure a solar $pp$ neutrino flux of $(10.2 \pm 2.0) \times 10^{10}$ cm$^{-2}$ s$^{-1}$. | result 1.00 | 0.97 | 0.44 | asserted 1.00 |
| s3 | The result is larger, but statistically consistent with the previous measurement by Borexino at $1.9\sigma$. | interpretation 0.74 | 0.64 | 0.07 | hedged possibility 0.50 |
| s4 | Together with recent observations of coherent elastic neutrino-nucleus scattering of $^8$B solar neutrinos in XENONnT and other liquid-xenon time projection chambers, these results demonstrate the growing potential of liquid xenon detectors for neutrino physics down to the keV-scale and represent an important milestone towards a next-generation multipurpose observatory. | interpretation 1.00 | 0.49 | 0.31 | asserted 1.00 |
What was examined, and what was not
- arXiv listing abstract v1
- full text
- figures and tables
- references and citing sentences
- relations to other papers
- P abstract
- S sections
- T body sentences
- C citations
- R cross-paper relations
References
How the literature uses it
What this paper does with the arXiv papers it cites
What it cites · 62 sentences without a confident label
Uses the method or tool of 9 papers
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The signal efficiency was evaluated using XENONnT's open source waveform simulation framework [ref] in combination with [220]Rn calibration data [ref] .
XENONnT Analysis: Signal Reconstruction, Calibration and Event Selection · Data and signal efficiency · 0.97
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A cross-section model based on the Relativistic Random Phase Approximation (RRPA) has been introduced as a refinement [ref] .
Low-energy electronic recoil in xenon detectors by solar neutrinos · SOLAR NEUTRINO RESULT WITH THE RRPA SIGNAL MODEL · 0.81
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They are calibrated independently for each science run using several monoenergetic calibration lines [ref] .
2502.18005 · Data and signal efficiency · 0.83
Uses data or values from 13 papers
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Consequently, the dominant background remaining in the solar neutrino analysis is [222]Rn, whose specific activity was reduced for the first time by using a dedicated radon removal system to about 0.9 [ref] , which is equivalent to the expected solar neutrino interaction rate in XENONnT.
Radon Removal in XENONnT down to the Solar Neutrino Level · Experiment · 0.92
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The fraction for each flux component is fixed according to the theoretical high-metallicity SSM (B16-GS98) [ref] , giving a solar $pp$ component fraction of within the ROI.
Solar Models: current epoch and time dependences, neutrinos, and helioseismological properties · Solar neutrino signal · 0.98
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During this period, the activity ratio, $^214$Pb/$^222$Rn, is evaluated as $0.66 ±0.03$ based on the slope obtained from the fit and accounting for the detector effects as well as the branching ratio of the decay to the ground state [ref] .
Direct Measurement of the $^{212}\mathrm{Pb}$ and $^{214}\mathrm{Pb}$ $\beta$ Decay Branching Ratios with the XENONnT Experiment · Lead-214 and lead-212 · 0.86
Compares with 3 papers
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The result is compared with the measurements from other experiments as well as the prediction from the B16-GS98 SSM [ref] in Fig. [ref].
A new Generation of Standard Solar Models · Results and Discussion · 0.92
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As the $^124$Xe spectra are distinctly peak-shaped, their rates are left free with a fixed branching ratio, such that the derived half-life can be compared to the literature measurements and theoretical prediction [ref] .
2402.13784 · XENON-124 DEC HALF-LIFE MEASUREMENT · 0.93
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Note Added – We note the recent preprint from the PandaX-4T Collaboration reporting on a similar result of elastic solar neutrino-electron scattering with a significance of 2.2 $σ$ [ref] .
Measurement of solar $pp$ neutrino flux with the new PandaX-4T data · Acknowledgments · 0.87
Cites as background 8 papers
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Since the pioneering detection by the Homestake experiment in 1968 [ref] , solar neutrinos and their properties have been primarily studied by experiments utilizing tens of tonnes of Gallium (SAGE [ref] , GALLEX/GNO [ref] ), or hundreds of tonnes of liquid scintillator (Borexino [ref] , KamLAND [ref] ), water (Super-Kamiokande [ref] ) or heavy water (SNO experiment [ref] ) as target material, whose large target masses compensate for the extremely small neutrino interaction probability.
Reanalysis of the GALLEX solar neutrino flux and source experiments · Introduction · 0.96
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Since the pioneering detection by the Homestake experiment in 1968 [ref] , solar neutrinos and their properties have been primarily studied by experiments utilizing tens of tonnes of Gallium (SAGE [ref] , GALLEX/GNO [ref] ), or hundreds of tonnes of liquid scintillator (Borexino [ref] , KamLAND [ref] ), water (Super-Kamiokande [ref] ) or heavy water (SNO experiment [ref] ) as target material, whose large target masses compensate for the extremely small neutrino interaction probability.
Measurement of the 8B Solar Neutrino Flux with the KamLAND Liquid Scintillator Detector · Introduction · 0.96
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Since the pioneering detection by the Homestake experiment in 1968 [ref] , solar neutrinos and their properties have been primarily studied by experiments utilizing tens of tonnes of Gallium (SAGE [ref] , GALLEX/GNO [ref] ), or hundreds of tonnes of liquid scintillator (Borexino [ref] , KamLAND [ref] ), water (Super-Kamiokande [ref] ) or heavy water (SNO experiment [ref] ) as target material, whose large target masses compensate for the extremely small neutrino interaction probability.
Combined Analysis of all Three Phases of Solar Neutrino Data from the Sudbury Neutrino Observatory · Introduction · 0.96
Discussion
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