arxiv: 2604.19616 · v2 · submitted 2026-04-21 · ✦ hep-ex

Recognition: unknown

Radon-induced backgrounds in the NEXT-100 experiment

A. Brodoline, A. Castillo, A.F.B. Isabel, A. Larumbe, A.L.M. Silva, A. Marauri, A. Mart\'inez, A. Para, A. Pazos, A.P. Marques, A. Sim\'on, A. Trettin, A. Yubero-Navarro, B.J.P. Jones, B. Palmeiro, B. Romeo, C.A.N. Conde, C.A.O. Henriques, C.D.R. Azevedo, C. Echeverria, C. Herv\'es Carrete, C.M.B. Monteiro, C. Rogero, C. Romo-Luque, C. Tonnel\'e, D.R. Nygren, E. Church, E. Dey, E. Oblak, E. Ruiz-Ch\'oliz, F. Auria-Luna, F. Ballester, F.I.G.M. Borges, F.J. Mora, F. Kellerer, F. Lopez, F. Monrabal, F.P. Coss\'io, F.P. Santos, F.W. Foss, G. Mart\'inez-Lema, H. Almaz\'an, I.J. Arnquist, I. Osborne, I. Parmaksiz, I. Rivilla, I. Shomroni, J.A. Hernando Morata, J.D. Villamil, J.E. Barcelon, J.F.C.A. Veloso, J.F. Toledo, J. Garc\'ia-Barrena, J. Hauptman, J.J. G\'omez-Cadenas, J. Mart\'in-Albo, J.M. Benlloch-Rodr\'iguez, J.M.F. dos Santos, J. Molina-Canteras, J.M.R. Teixeira, J. Palacio, J. Pelegrin, J. Renner, J. Soto-Oton, J. Torrent, J. Waiton, J.W.R. Grocott, K.E. Navarro, K. Mistry, L. Arazi, L. Larizgoitia, L.M.P. Fernandes, L.M. Villar Padruno, L. Rogers, M. Cid, M. del Barrio-Torregrosa, M. Elorza, M. Mart\'inez-Vara, M. P\'erez Maneiro, M. Querol, M. Seemann, M. Sorel, M. Vanga, N. Byrnes, NEXT Collaboration: C. Cortes-Parra, N. L\'opez-March, P.A.O.C. Silva, P. Dietz, P. Ferrario, P. Ferrero Manche\~no, P. Herrero-G\'omez, P. Lebrun, P. Novella, P.R.G. Valle, P. Saharia, P. V\'azquez Cabaleiro, R. Coupe, R.D.P. Mano, R. Esteve, R. Felkai, R. Guenette, R.L. Miller, R. Madigan, S. Ayet, S.R. Soleti, S. Teruel-Pardo, S. Torelli, V. \'Alvarez, V. Herrero, X. Cid, Y. Ayyad, Y. Ifergan, Z. Freixa

Pith reviewed 2026-05-10 00:51 UTC · model grok-4.3

classification ✦ hep-ex

keywords radon backgroundNEXT-100neutrinoless double beta decayhigh-pressure xenon TPCBi-214plate-outbackground indextopological selection

0 comments

The pith

The radon-induced background index in NEXT-100 drops to ~4×10^{-5} counts/(keV·kg·yr) after a topological cut selecting single double-electron tracks in the 0νββ region of interest.

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

The paper measures the contribution of radon to backgrounds in the NEXT-100 high-pressure xenon time projection chamber built for a neutrinoless double beta decay search. It reports an internal Rn-222 activity of 0.95 Bq/m³ that produces Bi-214 events after plate-out on the cathode, yielding a background index of 7.3×10^{-4} counts/(keV·kg·yr) once fully contained events are selected. A further topological requirement of exactly one double-electron-like track lowers the index to ~4×10^{-5} counts/(keV·kg·yr), an order of magnitude below the total expected radiogenic background. Correlation studies with airborne radon confirm that the LSC abatement system renders the detector environment virtually radon-free, with no detectable Rn-220.

Core claim

The central claim is that radon-induced Bi-214 events from Rn-222 plate-out on the cathode set a background index of (7.3 ± 1.5 stat ± 0.8 sys) × 10^{-4} counts/(keV·kg·yr) in the neutrinoless double beta decay region of interest after full-containment selection. Imposing a topological selection that accepts only events with a single double-electron-like track reduces this index to approximately 4 × 10^{-5} counts/(keV·kg·yr). This value lies one order of magnitude below the total radiogenic background expectation for NEXT-100. The internal Rn-222 activity is measured to be (0.95 ± 0.04 stat ± 0.09 sys) Bq/m³ with no observed Rn-220, and the detector operates in a virtually radon-free state.

What carries the argument

The topological selection that requires exactly one double-electron-like track, applied after a fully-contained event cut, which suppresses the Bi-214 decays from radon progeny plate-out on the cathode surface.

If this is right

The measured background level after topological selection is low enough to support a competitive sensitivity for the 0νββ decay search in NEXT-100.
The detector benefits from an effective radon abatement system that keeps internal activity at the 1 Bq/m³ level.
No measurable contribution from Rn-220 is present in the data.
The plate-out rate of Rn-222 progeny on the cathode is quantified at 0.97 Hz for visible energies above 400 keV.

Where Pith is reading between the lines

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

Cathode surface passivation or coatings could further reduce the plate-out contribution in subsequent runs or scaled detectors.
The same containment-plus-single-track topology cut may transfer directly to other high-pressure xenon TPCs used for rare-event searches.
Maintaining the reported containment and topology efficiencies at larger detector masses would keep radon backgrounds sub-dominant.

Load-bearing premise

That events above 400 keV are correctly attributed to Bi-214 from Rn-222 progeny plate-out on the cathode and that the Monte Carlo simulation accurately models both the containment efficiency and the topological selection efficiency without large unaccounted biases.

What would settle it

A direct measurement in which the background index after the single double-electron-track topological selection exceeds 10^{-4} counts/(keV·kg·yr) or shows no correlation with the measured airborne radon activity would falsify the reported reduction and the claim of a virtually radon-free environment.

read the original abstract

The NEXT-100 detector at the LSC aims at the first competitive search for the \bbnonu decay using a high-pressure \Xe{136} electroluminescent time projection chamber. The first low-background run of NEXT-100 at 3.95 bar has been devoted to the measurement of the radon-induced backgrounds impacting this search. The contributions from both the internal and external airborne radon have been evaluated. The internal \Rn{222} activity is found to be (0.95$\pm$0.04(stat)$\pm$0.09(sys)) Bq/m$^3$, while no traces of \Rn{220} have been observed. Most of the \Rn{222} progeny plate-out on the surface of the cathode of the detector, leading to a rate of Rn-induced \Bi{214} of (0.97$\pm$0.05(stat)$\pm$0.10(sys)) Hz for visible energies above 400 keV. The corresponding background index in the \bbnonu region of interest is evaluated as (7.3$\pm$1.5(stat)$\pm$0.8(sys))$\times10^{-4}$ counts/(keV$\cdot$kg$\cdot$yr) after selection of the fully contained events. This background index is reduced to $\sim$4$\times10^{-5}$ counts/(keV$\cdot$kg$\cdot$yr) by applying a topological selection requiring only one double-electron-like track in the events. This value is one order of magnitude below the total radiogenic background expectation in NEXT-100. By analyzing the correlation of the airborne radon activity and the measured rate of events in NEXT-100, it is concluded that the detector operates in a virtualy radon-free environment thanks to the radon abatement system of the LSC.

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

This paper gives the first direct measurements of radon activity and Bi-214 rates in NEXT-100, showing the topological cut drops the background index to ~4e-5 in the 0νββ ROI.

read the letter

The main thing to know is that NEXT-100 has measured its internal Rn-222 at 0.95 Bq/m³ and the resulting Bi-214 rate at 0.97 Hz above 400 keV, then shown that a single double-electron track cut reduces the background index in the region of interest from 7.3×10^{-4} down to about 4×10^{-5} counts/(keV·kg·yr). That puts the radon contribution an order of magnitude below the expected total radiogenic background, which supports their claim that the detector runs effectively radon-free thanks to the LSC abatement system. No Rn-220 shows up in the data either. These are concrete, new numbers tied to actual detector runs at 3.95 bar, with the correlation between external radon levels and internal event rates adding some credibility to the attribution of events to cathode plate-out. The reduction factor matches what one would expect from the topological selection against Bi-214 decays. The paper does a decent job reporting both statistical and systematic uncertainties on the key rates. The soft spots are the standard ones for TPC background papers. The final index depends on Monte Carlo modeling of containment and selection efficiencies, so any mismatch between simulation and real track reconstruction or energy response could affect the scaled result. The assumption that most visible events above 400 keV come from Rn progeny plate-out is plausible from the rates but would need careful checks in the full analysis for possible contamination from other sources. Nothing in the summary suggests a load-bearing flaw, and the errors look transparently quoted. This paper is mainly useful for the NEXT collaboration and other groups running or planning high-pressure xenon TPCs for double beta decay searches. A reader working on background budgets in similar underground detectors would get practical value from the measured activities and the demonstrated rejection power. It is not broad enough for a general audience. I would bring it to a reading group focused on experimental techniques if the group is interested in xenon TPCs. I would not cite it in my own work unless I needed the specific NEXT-100 numbers for comparison. It deserves peer review because the measurements are new, relevant to the experiment's sensitivity, and appear to rest on direct data rather than circular fitting.

Referee Report

2 major / 3 minor

Summary. The manuscript reports measurements of radon-induced backgrounds in the NEXT-100 high-pressure xenon electroluminescent TPC for neutrinoless double beta decay searches. It finds an internal Rn-222 activity of (0.95 ± 0.04(stat) ± 0.09(sys)) Bq/m³ with no detectable Rn-220, a Rn-induced Bi-214 rate of (0.97 ± 0.05(stat) ± 0.10(sys)) Hz above 400 keV from cathode plate-out, a background index of (7.3 ± 1.5(stat) ± 0.8(sys)) × 10^{-4} counts/(keV·kg·yr) in the 0νββ ROI after fully-contained event selection, and a reduction to ~4 × 10^{-5} counts/(keV·kg·yr) via a topological cut requiring a single double-electron-like track. The analysis concludes that the LSC radon abatement system renders the detector virtually radon-free, with this background an order of magnitude below the total radiogenic expectation.

Significance. If the results hold, the work is significant for establishing that radon backgrounds are sub-dominant in NEXT-100, directly supporting the experiment's projected sensitivity for 0νββ decay. The direct correlation between external airborne radon measurements and internal event rates, combined with quantified statistical and systematic uncertainties on the activity and background index, provides a robust validation of the background model and mitigation strategy.

major comments (2)

[Analysis of Bi-214 rate and background index evaluation] The scaling from the measured Bi-214 rate (0.97 Hz above 400 keV) to the quoted background index of 7.3 × 10^{-4} counts/(keV·kg·yr) in the 0νββ ROI relies on containment and topological efficiencies that are modeled but not cross-validated in detail against data; this is load-bearing for the central claim of an 18× reduction factor and the conclusion that radon is sub-dominant.
[Event rate measurement and source identification] The attribution of all events above 400 keV to Bi-214 from Rn-222 progeny plate-out on the cathode assumes no significant contribution from other sources or partial energy depositions; the paper should quantify any residual contamination or alternative origins to confirm the rate-to-BI conversion is unbiased.

minor comments (3)

Specify the exact energy window and fiducial volume definition used for the 0νββ ROI when computing the background index.
Clarify whether the topological selection efficiency (~18× rejection) includes any data-MC discrepancies or additional systematic uncertainties beyond those quoted.
Add a reference or brief description of the radon abatement system at LSC to support the 'virtually radon-free' conclusion.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We are grateful to the referee for the positive evaluation of our manuscript and for the detailed comments, which have helped us improve the presentation of our results. Below we provide point-by-point responses to the major comments. We have revised the manuscript accordingly to address the concerns raised.

read point-by-point responses

Referee: [Analysis of Bi-214 rate and background index evaluation] The scaling from the measured Bi-214 rate (0.97 Hz above 400 keV) to the quoted background index of 7.3 × 10^{-4} counts/(keV·kg·yr) in the 0νββ ROI relies on containment and topological efficiencies that are modeled but not cross-validated in detail against data; this is load-bearing for the central claim of an 18× reduction factor and the conclusion that radon is sub-dominant.

Authors: We thank the referee for highlighting this important aspect of our analysis. The containment efficiency and the topological selection efficiency are derived from detailed Monte Carlo simulations of Bi-214 decays distributed according to the plate-out model on the cathode. These simulations have been cross-validated with data in several ways: (1) the overall event rate and energy spectrum match the observed data after accounting for the measured radon activity; (2) calibration data from external sources confirm the tracking and energy reconstruction performance used in the efficiencies. However, to make this validation more explicit, we will add a dedicated subsection in the revised manuscript describing the comparison between data and simulation for the key selection variables, such as the number of tracks and energy containment. This will support the quoted 18× reduction factor (from 7.3×10^{-4} to ~4×10^{-5} counts/(keV·kg·yr)) and reinforce that radon is sub-dominant to other radiogenic backgrounds. revision: partial
Referee: [Event rate measurement and source identification] The attribution of all events above 400 keV to Bi-214 from Rn-222 progeny plate-out on the cathode assumes no significant contribution from other sources or partial energy depositions; the paper should quantify any residual contamination or alternative origins to confirm the rate-to-BI conversion is unbiased.

Authors: We agree that a clear quantification of potential alternative contributions is valuable. The events above 400 keV are selected in a fiducial volume and their energy spectrum is fitted to the expected Bi-214 beta decay spectrum, yielding excellent agreement with no significant residuals. Material radioassay results for the detector components show that contributions from other isotopes (e.g., U/Th chains in the field cage or PMTs) are expected to be at least an order of magnitude lower in this energy range. Partial energy depositions from external gammas are suppressed by the high-pressure xenon and the topological requirements. In the revised version, we will include an explicit upper limit on any non-Bi-214 contribution, derived from the spectrum fit residuals and screening data, to confirm that the rate-to-background-index conversion remains unbiased. revision: yes

Circularity Check

0 steps flagged

No significant circularity

full rationale

The derivation chain starts from direct measurements of Rn-222 activity (0.95 Bq/m³) and Bi-214 rate (0.97 Hz above 400 keV) extracted from detector data and correlated with external airborne radon readings. These rates are then scaled to the 0νββ ROI background index using standard Monte Carlo-derived containment and topological efficiencies, without any parameter fitting that re-uses the target index as input. No self-definitional equations, fitted inputs renamed as predictions, or load-bearing self-citations appear; the final reduced index (~4×10^{-5}) follows from applying the single-track cut to the measured sample and is externally falsifiable against the observed event counts.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

The central claims rest on experimental data from the detector run and correlation with external radon monitoring. No new entities are postulated.

axioms (1)

domain assumption The LSC radon abatement system reduces airborne radon to negligible levels inside the detector.
This is used to interpret the low measured activity and conclude virtually radon-free operation.

pith-pipeline@v0.9.0 · 6308 in / 1464 out tokens · 71108 ms · 2026-05-10T00:51:10.117689+00:00 · methodology

discussion (0)

Reference graph

Works this paper leans on

28 extracted references · 28 canonical work pages

[1]

The search for neutrinoless double-beta decay

G \'o mez-Cadenas, Juan Jos \'e and Mart \' n-Albo, Justo and Men \'e ndez, Javier and Mezzetto, Mauro and Monrabal, Francesc and Sorel, Michel. The search for neutrinoless double-beta decay. Riv. Nuovo Cim. 2023. doi:10.1007/s40766-023-00049-2

work page doi:10.1007/s40766-023-00049-2 2023
[2]

Precise Half-Life Values for Two-Neutrino Double- Decay: 2020 Review

Barabash, Alexander. Precise Half-Life Values for Two-Neutrino Double- Decay: 2020 Review. Universe. 2020. doi:10.3390/universe6100159. arXiv:2009.14451

work page doi:10.3390/universe6100159 2020
[3]

and others

Abe, S. and others. Search for Majorana Neutrinos with the Complete KamLAND-Zen Dataset. Phys. Rev. Lett. 2025. doi:10.1103/jkf6-48j8. arXiv:2406.11438

work page doi:10.1103/jkf6-48j8 2025
[4]

and others

Monrabal, F. and others. The Next White (NEW) Detector. JINST. 2018. doi:10.1088/1748-0221/13/12/P12010. arXiv:1804.02409

work page doi:10.1088/1748-0221/13/12/p12010 2018
[5]

and others

Renner, J. and others. Energy calibration of the NEXT-White detector with 1\ resolution near Q _ of ^ 136 Xe. JHEP. 2019. doi:10.1007/JHEP10(2019)230. arXiv:1905.13110

work page doi:10.1007/jhep10(2019)230 2019
[6]

and Wingfield, E

Redshaw, M. and Wingfield, E. and McDaniel, J. and Myers, E. G. Mass and double-beta-decay Q value of Xe-136. Phys. Rev. Lett. 2007. doi:10.1103/PhysRevLett.98.053003

work page doi:10.1103/physrevlett.98.053003 2007
[7]

and others

Ferrario, P. and others. Demonstration of the event identification capabilities of the NEXT-White detector. JHEP. 2019. doi:10.1007/JHEP10(2019)052. arXiv:1905.13141

work page doi:10.1007/jhep10(2019)052 2019
[8]

Kekic, et al., Demonstration of background rejection using deep convolutional neural networks in the NEXT experiment, JHEP 01 (2021) 189

Kekic, M. and others. Demonstration of background rejection using deep convolutional neural networks in the NEXT experiment. JHEP. 2021. doi:10.1007/JHEP01(2021)189. arXiv:2009.10783

work page doi:10.1007/jhep01(2021)189 2021
[9]

and others

Sim\'on, A. and others. Boosting background suppression in the NEXT experiment through Richardson-Lucy deconvolution. JHEP. 2020. doi:10.1007/JHEP07(2021)146. arXiv:2102.11931

work page doi:10.1007/jhep07(2021)146 2020
[10]

and others

Novella, P. and others. Measurement of radon-induced backgrounds in the NEXT double beta decay experiment. JHEP. 2018. doi:10.1007/JHEP10(2018)112. arXiv:1804.00471

work page doi:10.1007/jhep10(2018)112 2018
[11]

and others

Novella, P. and others. Radiogenic Backgrounds in the NEXT Double Beta Decay Experiment. JHEP. 2019. doi:10.1007/JHEP10(2019)051. arXiv:1905.13625

work page doi:10.1007/jhep10(2019)051 2019
[12]

and others

Novella, P. and others. Measurement of the Xe136 two-neutrino double- -decay half-life via direct background subtraction in NEXT. Phys. Rev. C. 2022. doi:10.1103/PhysRevC.105.055501. arXiv:2111.11091

work page doi:10.1103/physrevc.105.055501 2022
[13]

and others

Novella, P. and others. Demonstration of neutrinoless double beta decay searches in gaseous xenon with NEXT. JHEP. 2023. doi:10.1007/JHEP09(2023)190. arXiv:2305.09435

work page doi:10.1007/jhep09(2023)190 2023
[14]

and others

Mart\' n-Albo, J. and others. Sensitivity of NEXT-100 to Neutrinoless Double Beta Decay. JHEP. 2016. doi:10.1007/JHEP05(2016)159. arXiv:1511.09246

work page doi:10.1007/jhep05(2016)159 2016
[15]

and others

Adams, C. and others. The NEXT-100 Detector. Eur. Phys. J. C. 2026. doi:10.1140/epjc/s10052-025-14951-y. arXiv:2505.17848

work page doi:10.1140/epjc/s10052-025-14951-y 2026
[16]

and others

Adams, C. and others. Sensitivity of a tonne-scale NEXT detector for neutrinoless double beta decay searches. JHEP. 2021. doi:https://doi.org/10.1007/JHEP08(2021)164. arXiv:2005.06467

work page doi:10.1007/jhep08(2021)164 2021
[17]

Wu, S. -C. Nuclear Data Sheets for A = 214. Nucl. Data Sheets. 2009. doi:10.1016/j.nds.2009.02.002

work page doi:10.1016/j.nds.2009.02.002 2009
[18]

and Singh, Balraj

Jain, Ashok K. and Singh, Balraj. Nuclear Data Sheets for A = 218. Nucl. Data Sheets. 2006. doi:10.1016/j.nds.2006.03.002

work page doi:10.1016/j.nds.2006.03.002 2006
[19]

Nuclear Data Sheets for A = 210

Shamsuzzoha Basunia, M. Nuclear Data Sheets for A = 210. Nucl. Data Sheets. 2014. doi:10.1016/j.nds.2014.09.004

work page doi:10.1016/j.nds.2014.09.004 2014
[20]

and others

Argyriades, J. and others. Measurement of the background in the NEMO 3 double beta decay experiment. Nucl. Instrum. Meth. A. 2009. doi:10.1016/j.nima.2009.04.011. arXiv:0903.2277

work page doi:10.1016/j.nima.2009.04.011 2009
[21]

Radon Mitigation Applications at the Laboratorio Subterr \'a neo de Canfranc (LSC)

P \'e rez-P \'e rez, Javier and others. Radon Mitigation Applications at the Laboratorio Subterr \'a neo de Canfranc (LSC). Universe. 2022. doi:10.3390/universe8020112. arXiv:2112.15371

work page doi:10.3390/universe8020112 2022
[22]

and others

Mart \' nez-Lema, G. and others. First results of the NEXT-100 detector using ^ 83m Kr decays. 2025. arXiv:2511.01710

work page arXiv 2025
[23]

and others

P \'e rez Maneiro, M. and others. Demonstration of Sub-Percent Energy Resolution in the NEXT-100 Detector. 2025. arXiv:2511.02467

work page arXiv 2025
[24]

Albert, J. B. and others. Measurements of the ion fraction and mobility of - and -decay products in liquid xenon using the EXO-200 detector. Phys. Rev. 2015. doi:10.1103/PhysRevC.92.045504. arXiv:1506.00317

work page doi:10.1103/physrevc.92.045504 2015
[25]

GEANT4—a simulation toolkit

Agostinelli, S. and others. GEANT4: A Simulation toolkit. Nucl. Instrum. Meth. 2003. doi:10.1016/S0168-9002(03)01368-8

work page doi:10.1016/s0168-9002(03)01368-8 2003
[26]

and Borjabad, S

Bandac, I. and Borjabad, S. and Ianni, A. and Nu\ nez-Lagos, R. and P\'erez, C. and Rodr\'iguez, S. and Villar, J. A. Ultra-low background and environmental measurements at Laboratorio Subterr\'aneo de Canfranc (LSC). Appl. Radiat. Isot. 2017. doi:10.1016/j.apradiso.2017.02.046

work page doi:10.1016/j.apradiso.2017.02.046 2017
[27]

and others

Mistry, K. and others. Design, characterization and installation of the NEXT-100 cathode and electroluminescence regions. JINST. 2024. doi:10.1088/1748-0221/19/02/P02007. arXiv:2311.03528

work page doi:10.1088/1748-0221/19/02/p02007 2024
[28]

and others

Serra, L. and others. An improved measurement of electron-ion recombination in high-pressure xenon gas. JINST. 2015. doi:10.1088/1748-0221/10/03/P03025. arXiv:1412.3573

work page doi:10.1088/1748-0221/10/03/p03025 2015