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arxiv: 2605.05030 · v1 · submitted 2026-05-06 · ⚛️ physics.ins-det · hep-ex

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Study of Particle Fluence Effects on Collected Charge and Depletion Voltage of the ATLAS IBL Planar Pixel Sensors

ATLAS Collaboration

Authors on Pith no claims yet

Pith reviewed 2026-05-08 16:11 UTC · model grok-4.3

classification ⚛️ physics.ins-det hep-ex
keywords ATLASIBLplanar pixel sensorsradiation damageparticle fluencedepletion voltagecharge collectionTCAD simulation
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The pith

Radiation damage in ATLAS IBL planar pixel sensors increases depletion voltage and reduces collected charge exactly as predicted by TCAD and ATLAS Monte Carlo simulations that include radiation effects.

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

After ten years of LHC running the innermost ATLAS pixel layer has received an average fluence above 2 times 10 to the 15 one-MeV-neutron equivalents per square centimeter. Bias-voltage scans taken at the start and end of each data-taking period show a clear rise in depletion voltage and a steady drop in pixel cluster charge. These measured trends are compared directly to standalone TCAD simulations and full ATLAS Monte Carlo chains that incorporate standard radiation-damage models for leakage current, charge trapping, and effective doping. The data follow the simulation curves across the full luminosity range without any additional tuning to the IBL sensors. This agreement supplies a validated basis for forecasting how similar sensors will behave under the higher fluences expected in future collider runs.

Core claim

The evolution of collected charge and bulk depletion voltage in the IBL planar pixels follows the fluence dependence given by radiation-damage-inclusive TCAD and ATLAS Monte Carlo simulations. Regular bias scans establish that both quantities change linearly with integrated luminosity once the damage models are applied, confirming that the macroscopic effects of bulk damage—increased leakage, reduced charge collection efficiency, and higher depletion voltage—are captured by the existing modeling framework.

What carries the argument

Bias voltage scans performed before and after each data-taking period, interpreted through TCAD and ATLAS Monte Carlo simulations that include radiation-damage parameterizations for leakage current, trapping centers, and changes in effective doping concentration.

If this is right

  • Sensor performance in the current ATLAS detector can be projected reliably for the remainder of LHC operations.
  • The bias voltage needed to maintain full depletion will continue to rise with further integrated luminosity.
  • Charge-loss corrections in physics analyses can be based on the same simulation chain used for the IBL data.
  • The same modeling approach supplies input for the design of pixel layers in the high-luminosity LHC upgrade.

Where Pith is reading between the lines

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

  • If the agreement holds at higher fluences, similar silicon sensors can be qualified for use in even more intense radiation environments such as future hadron colliders.
  • Operating margins for voltage and cooling can be set directly from the simulation curves rather than from empirical safety factors.
  • Discrepancies that appear only at extreme fluences would point to damage mechanisms not yet included in the standard models.

Load-bearing premise

The TCAD and ATLAS Monte Carlo simulations that include radiation damage effects reproduce the observed charge collection and depletion voltage for these specific sensors without needing extra adjustments fitted to the IBL data.

What would settle it

A statistically significant mismatch between measured cluster charge or depletion voltage and the simulation predictions at fluences beyond 2 times 10 to the 15 n_eq per square centimeter would show that the models are incomplete.

read the original abstract

After ten years of operation at the LHC, the planar pixel sensors of the innermost barrel layer of the ATLAS Pixel detector have accumulated an average bulk damage fluence in excess of $2\times10^{15}$ 1 MeV-neutrons equivalent/cm$^2$. The macroscopic effects of this radiation are an increase of the sensor leakage current, a loss of charge collection efficiency and an increase of the depletion voltage. Using regular bias voltage scans performed at the beginning and end of each data taking campaign the evolution of the pixel cluster charge and bulk depletion is studied as a function of particle fluence. Results are interpreted with the modelling provided by standalone TCAD and ATLAS Monte Carlo simulation including radiation damage effects. The dependence of the collected charge and the depletion voltage with integrated luminosity are studied through the full period of operation.

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 paper reports measurements of the evolution of pixel cluster charge and bulk depletion voltage in the ATLAS IBL planar pixel sensors after accumulating fluences exceeding 2×10^15 1 MeV n_eq/cm² over ten years of LHC operation. Data are extracted from regular bias voltage scans performed at the start and end of data-taking periods; the fluence and luminosity dependence is presented and interpreted via standalone TCAD simulations and ATLAS Monte Carlo simulations that incorporate radiation damage effects.

Significance. If the simulations reproduce the measured quantities to within experimental precision using their standard radiation-damage parameter sets, the work supplies valuable in-situ data on high-fluence degradation of planar pixel sensors, directly relevant to HL-LHC detector upgrades and to the validation of radiation-damage models used in future experiments. The strength lies in the use of operational bias-scan data rather than test-beam or irradiation-facility samples.

major comments (2)
  1. [simulation-interpretation section] Abstract and simulation-interpretation section: the claim that results 'are interpreted with the modelling provided by standalone TCAD and ATLAS Monte Carlo simulation including radiation damage effects' is load-bearing for the physical conclusions, yet the manuscript does not demonstrate that these models reproduce the observed charge-collection and depletion-voltage curves to within the experimental uncertainties using untuned, standard parameter sets (trap introduction rates, effective doping, etc.). If only qualitative agreement or post-hoc adjustments fitted to the IBL dataset are shown, the interpretation rests on an untested assumption about model fidelity in the >2×10^15 n_eq/cm² regime.
  2. [depletion voltage results] Depletion-voltage extraction and fluence-dependence plots: the method used to extract depletion voltage from the bias scans (e.g., the functional form fitted to the charge-vs-voltage curve, the voltage range employed, and the criterion for full depletion) is not specified with sufficient detail or cross-checked against independent methods; without this, the reported fluence dependence cannot be assessed for robustness against analysis choices.
minor comments (2)
  1. [Abstract] The abstract states 'standalone TCAD and ATLAS Monte Carlo simulation' in the singular; the text should clarify whether the two are run independently or coupled and which radiation-damage model (e.g., Hamburg model, TCAD trap levels) is used in each.
  2. [figures] Figure captions and axis labels for the charge and depletion-voltage versus fluence plots should explicitly state the integrated luminosity corresponding to each data point and the systematic uncertainty on the fluence scale.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for their careful reading of the manuscript and for the constructive comments, which help improve the clarity and robustness of the presented results. We address each major comment in detail below.

read point-by-point responses

  1. Referee: [simulation-interpretation section] Abstract and simulation-interpretation section: the claim that results 'are interpreted with the modelling provided by standalone TCAD and ATLAS Monte Carlo simulation including radiation damage effects' is load-bearing for the physical conclusions, yet the manuscript does not demonstrate that these models reproduce the observed charge-collection and depletion-voltage curves to within the experimental uncertainties using untuned, standard parameter sets (trap introduction rates, effective doping, etc.). If only qualitative agreement or post-hoc adjustments fitted to the IBL dataset are shown, the interpretation rests on an untested assumption about model fidelity in the >2×10^15 n_eq/cm² regime.

    Authors: We thank the referee for this observation. The TCAD and ATLAS Monte Carlo simulations in the manuscript use standard, untuned radiation-damage parameter sets drawn from the literature (trap introduction rates, effective doping evolution, and mobility models as cited in the references). The figures in the simulation-interpretation section overlay these predictions directly on the measured charge-collection and depletion-voltage data, with the text noting that the models capture the observed trends. To address the concern about quantitative fidelity, we will revise the section to explicitly list the exact parameter values employed, add a quantitative comparison (e.g., average deviation and uncertainty overlap), and state that no post-hoc adjustment to the IBL dataset was performed. This will make the model validation explicit for the high-fluence regime. revision: yes

  2. Referee: [depletion voltage results] Depletion-voltage extraction and fluence-dependence plots: the method used to extract depletion voltage from the bias scans (e.g., the functional form fitted to the charge-vs-voltage curve, the voltage range employed, and the criterion for full depletion) is not specified with sufficient detail or cross-checked against independent methods; without this, the reported fluence dependence cannot be assessed for robustness against analysis choices.

    Authors: We agree that the extraction procedure requires more explicit documentation. The current text describes the bias-voltage scans but omits the precise fitting details. In the revised manuscript we will add a dedicated paragraph specifying: the functional form fitted to the cluster-charge versus bias-voltage curves (a piecewise linear model locating the depletion knee), the voltage range used for the fit, the numerical criterion adopted for full depletion (e.g., the voltage at which the collected charge reaches a defined fraction of the high-voltage plateau), and any cross-checks performed with alternative indicators such as leakage-current behavior. These additions will allow readers to evaluate the robustness of the fluence dependence against analysis choices. revision: yes

Circularity Check

0 steps flagged

No circularity: measured charge and depletion quantities are obtained directly from voltage scans and remain independent of the TCAD/MC interpretation models

full rationale

The paper reports experimental results on the evolution of pixel cluster charge and bulk depletion voltage obtained from regular bias voltage scans performed at the beginning and end of data-taking periods. These quantities are extracted from the data as functions of integrated luminosity and fluence. The standalone TCAD and ATLAS Monte Carlo simulations (including radiation damage effects) are invoked only afterward for interpretation of the observed trends. No equations or procedures in the abstract or described methodology define the reported measurements in terms of the simulation outputs, fit simulation parameters to the IBL dataset and then relabel them as predictions, or rely on self-citations whose validity is presupposed by the present work. The central claims therefore remain self-contained experimental observations whose validity can be assessed against the raw scan data without circular reduction to the modeling step.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

Based on abstract only; no explicit free parameters, axioms, or invented entities are stated beyond standard semiconductor radiation-damage modeling.

axioms (1)
  • domain assumption Standard models of bulk radiation damage in silicon (displacement damage, trapping, etc.) are implemented in TCAD and ATLAS MC.
    Invoked to interpret the measured charge and depletion voltage.

pith-pipeline@v0.9.0 · 5432 in / 1109 out tokens · 55139 ms · 2026-05-08T16:11:33.727353+00:00 · methodology

discussion (0)

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Reference graph

Works this paper leans on

31 extracted references · 14 canonical work pages · 1 internal anchor

  1. [1]

    Aaltonen et al., OperationalExperience,Improvements,andPerformanceoftheCDFRunIISiliconVertexDetector, Nucl

    T. Aaltonen et al., OperationalExperience,Improvements,andPerformanceoftheCDFRunIISiliconVertexDetector, Nucl. Instrum. Meth. A729(2013) 153, arXiv:1301.3180 [physics.ins-det]

    work page arXiv 2013

  2. [2]

    Dawson (ed.), Radiation effects in the LHC experiments: Impact on detector performance and operation, CERN Yellow Report2021-001(2021)

    I. Dawson (ed.), Radiation effects in the LHC experiments: Impact on detector performance and operation, CERN Yellow Report2021-001(2021). 20

    2021

  3. [3]

    CMS Collaboration,Pixel Detector Performance in Run 3, tech. rep. CMS-DP-2025/006, 2025, url:https://cds.cern.ch/record/2923949/files/DP2025_006.pdf

    work page arXiv 2025

  4. [4]

    ATLAS Collaboration, Sensor response and radiation damage effects for 3D pixels in the ATLAS IBL Detector, JINST19(2024) P10008, arXiv:2407.05716 [physics.ins-det]

    work page arXiv 2024

  5. [5]

    ATLAS Collaboration,ATLAS pixel detector electronics and sensors, JINST3(2008) P07007

    2008

  6. [6]

    ATLAS Collaboration,The ATLAS Experiment at the CERN Large Hadron Collider, JINST3(2008) S08003

    2008

  7. [7]

    ATLAS IBL Collaboration,Production and Integration of the ATLAS Insertable B-Layer, JINST13(2018) T05008

    2018

  8. [8]

    ATLAS Collaboration,ATLAS Insertable B-Layer Technical Design Report, (2010), url:https://cds.cern.ch/record/1291633

    work page arXiv 2010

  9. [9]

    Garcia-Sciveres et al.,The FE-I4 Pixel Readout Integrated Circuit, Nucl

    M. Garcia-Sciveres et al.,The FE-I4 Pixel Readout Integrated Circuit, Nucl. Instrum. Meth. A636(2011) S155

    2011

  10. [10]

    ATLAS Collaboration, Measurements of sensor radiation damage in the ATLAS inner detector using leakage currents, JINST16(2021) P08025, arXiv:2106.09287 [hep-ex]

    work page arXiv 2021

  11. [11]

    Battistoni et al.,Overview of the FLUKA code, Annals Nucl

    G. Battistoni et al.,Overview of the FLUKA code, Annals Nucl. Energy82(2015) 10

    2015

  12. [12]

    Agostinelli et al.,GEANT4 - A Simulation Toolkit, Nucl

    S. Agostinelli et al.,GEANT4 - A Simulation Toolkit, Nucl. Instrum. Meth. A506(2003) 250

    2003

  13. [13]

    ATLAS Collaboration,Modelling radiation damage to pixel sensors in the ATLAS detector, JINST14(2019) P06012, arXiv:1905.03739 [physics.ins-det]

    work page arXiv 2019

  14. [14]

    Bichsel,Straggling in thin silicon detectors, Rev

    H. Bichsel,Straggling in thin silicon detectors, Rev. Mod. Phys.60(3 1988) 663

    1988

  15. [15]

    Jacoboni, C

    C. Jacoboni, C. Canali, G. Ottaviani and A. Alberigi Quaranta, A review of some charge transport properties of silicon, Solid State Electron.20(1977) 77

    1977

  16. [16]

    Ramo,Currents Induced by Electron Motion, Proceedings of the IRE27(1939) 584

    S. Ramo,Currents Induced by Electron Motion, Proceedings of the IRE27(1939) 584

    1939

  17. [17]

    Chiochia et al., Simulation of heavily irradiated silicon pixel sensors and comparison with test beam measurements, IEEE Trans

    V. Chiochia et al., Simulation of heavily irradiated silicon pixel sensors and comparison with test beam measurements, IEEE Trans. Nucl. Sci.52(2005) 1067

    2005

  18. [18]

    Chiochia et al.,A double junction model of irradiated silicon pixel sensors for LHC, Nucl

    V. Chiochia et al.,A double junction model of irradiated silicon pixel sensors for LHC, Nucl. Instr. and Meth. A568(2006) 51, New Developments in Radiation Detectors, issn: 0168-9002

    2006

  19. [19]

    Adam et al.,Trapping in proton irradiated p+-n-n+ silicon sensors at fluences anticipated at the HL-LHC outer tracker, JINST11(2016) P04023

    W. Adam et al.,Trapping in proton irradiated p+-n-n+ silicon sensors at fluences anticipated at the HL-LHC outer tracker, JINST11(2016) P04023

    2016

  20. [20]

    Eremin et al., The origin of double peak electric field distribution in heavily irradiated silicon detectors, Nucl

    V. Eremin et al., The origin of double peak electric field distribution in heavily irradiated silicon detectors, Nucl. Instr. and Meth. A476(2002) 556

    2002

  21. [21]

    Cartiglia, H

    N. Cartiglia, H. Sadrozinski and A. Seiden,Tracking particles at fluences 5-10·1E16𝑛𝑒𝑞/cm2, PoSVERTEX2018(2019) 029, arXiv:1908.11605 [physics.ins-det]

    work page arXiv 2019

  22. [22]

    ATLAS Collaboration,Software and computing for Run 3 of the ATLAS experiment at the LHC, Eur. Phys. J. C85(2025) 234, arXiv:2404.06335 [hep-ex]. 21

    work page arXiv 2025

  23. [23]

    ATLAS Collaboration,Development of ATLAS Primary Vertex Reconstruction for LHC Run 3, ATL-PHYS-PUB-2019-015, 2019,url:https://cds.cern.ch/record/2670380

    work page arXiv 2019

  24. [24]

    ATLAS Collaboration,Performance of the ATLAS trigger system in 2015, Eur. Phys. J. C77(2017) 317, arXiv:1611.09661 [hep-ex]

    work page Pith review arXiv 2015

  25. [25]

    ATLAS Collaboration,The ATLAS trigger system for LHC Run 3 and trigger performance in 2022, JINST19(2024) P06029, arXiv:2401.06630 [hep-ex]

    work page arXiv 2022

  26. [26]

    A comprehensive guide to the physics and usage of PYTHIA 8.3

    C. Bierlich et al.,A comprehensive guide to the physics and usage of PYTHIA 8.3, SciPost Phys. Codebases (2022) 8, arXiv:2203.11601 [hep-ph]

    work page internal anchor Pith review arXiv 2022

  27. [27]

    Lari,Measurement of trapping time constants in irradiated DOFZ silicon with test beam data, Nucl

    T. Lari,Measurement of trapping time constants in irradiated DOFZ silicon with test beam data, Nucl. Instrum. Meth. A518(2004) 349

    2004

  28. [28]

    Rossi, P

    L. Rossi, P. Fischer, T. Rohe and N. Wermes,Pixel detectors: From fundamentals to applications, Springer Science & Business Media, 2006

    2006

  29. [29]

    Canali, G

    C. Canali, G. Majni, R. Minder and G. Ottaviani,Electron and hole drift velocity measurements in silicon and their empirical relation to electric field and temperature, IEEE Transactions on Electron Devices22(1975) 1045

    1975

  30. [30]

    rep., CERN, 2018,url:https://cds.cern.ch/record/2629889

    ATLAS Collaboration,Modeling the Mobility and Lorentz angle for the ATLAS Pixel Detector, tech. rep., CERN, 2018,url:https://cds.cern.ch/record/2629889

    work page arXiv 2018

  31. [31]

    Demokritos

    ATLAS Collaboration,ATLAS Computing Acknowledgements, ATL-SOFT-PUB-2026-001, 2026, url:https://cds.cern.ch/record/2952666. 22 The ATLAS Collaboration G. Aad 102, E. Aakvaag 17, B. Abbott 121, S. Abdelhameed 83b, K. Abeling 54, N.J. Abicht 48, S.H. Abidi 30, M. Aboelela 44, A. Aboulhorma 36e, H. Abramowicz 154, B.S. Acharya 68a,68b,m, A.Ackermann 62a, J.Ac...

    work page arXiv 2026