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arxiv: 2605.28558 · v1 · pith:BHH5ZYCCnew · submitted 2026-05-27 · ⚛️ physics.ins-det

Development and Characterization of a Time Projection Chamber Prototype for Neutron Oscillation Searches at the European Spallation Source

Blahoslav Rataj , Valentina Santoro , Anders Oskarsson , Matthias Holl , Verena Hehl , David Silvermyr This is my paper

Pith reviewed 2026-06-29 09:18 UTC · model grok-4.3

classification ⚛️ physics.ins-det
keywords time projection chamberneutron-antineutron oscillationpion trackingdE/dx measurementcosmic muon validationEuropean Spallation Sourceparticle identificationsub-centroid refit
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The pith

A time projection chamber prototype reaches 0.55 mm yz resolution and 16% dE/dx width for pion tracking in neutron-antineutron searches.

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

The paper develops a compact TPC prototype and tracking algorithm aimed at reconstructing charged pions from antineutron annihilation on carbon in the proposed HIBEAM experiment. Validation relies on cosmic-particle data treated as a minimum-ionizing reference, proton elastic-scattering measurements, and simulated crossing-track events. The work demonstrates sub-millimetre residuals, uniform dE/dx response, and a truncated-mean dE/dx distribution with roughly 16% relative width, plus a sub-centroid refit that narrows residuals from 1.30 mm to 0.55 mm. These results matter because they test whether the detector concept can supply both position and particle-identification information needed for a future rare-process search at a spallation source.

Core claim

The central claim is that the TPC prototype with zigzag readout, combined with the developed tracking algorithm, delivers sub-millimetre residual widths and robust charge sharing in cosmic data, produces a truncated-mean track-level dE/dx distribution that is approximately Gaussian with 16% relative width, and supports the sub-centroid refit technique that reduces yz residual width from 1.30 mm to 0.55 mm, thereby validating initial tracking performance for the charged-pion final states expected in antineutron annihilation.

What carries the argument

The sub-centroid refit technique, which divides each pad-row signal into four equal-y sub-centroids using the internal ADC time profile rather than a single charge-weighted centroid.

If this is right

  • Reconstructed tracks in experimental cosmic data exhibit sub-millimetre residual widths and uniform dE/dx across the drift volume.
  • The algorithm performs reliably on well-separated tracks but shows reduced performance on crossing or overlapping tracks and dense proton-scattering events.
  • Tilted proton tracks produce broader yz residuals due to time-extended pad-row signals, which the sub-centroid refit mitigates.
  • Energy-loss information extracted via truncated-mean dE/dx can be used for particle identification.

Where Pith is reading between the lines

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

  • If the muon reference accurately models minimum-ionizing pions, the observed dE/dx resolution should translate to the annihilation final states targeted by HIBEAM.
  • The sub-centroid refit approach may improve position resolution in other gaseous detectors that record time profiles within readout pads.
  • Further algorithm development focused on dense or overlapping topologies would be required before the prototype can handle the full range of expected event complexities.

Load-bearing premise

That cosmic-particle measurements are dominated by atmospheric muons serving as a minimum-ionizing reference for the pionic final states from antineutron annihilation.

What would settle it

A beam test that directly measures the truncated-mean dE/dx distribution for pions of similar momentum and compares its width and peak position to the cosmic-muon distribution would confirm or refute the 16% relative width claim.

Figures

Figures reproduced from arXiv: 2605.28558 by Anders Oskarsson, Blahoslav Rataj, David Silvermyr, Matthias Holl, Valentina Santoro, Verena Hehl.

Figure 1
Figure 1. Figure 1: Overview of the HIBEAM annihilation-detector concept. The TPC surrounds [PITH_FULL_IMAGE:figures/full_fig_p005_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: Schematic overview of the prototype readout and data-acquisition system, in [PITH_FULL_IMAGE:figures/full_fig_p008_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: Schematic illustration of the target–TPC geometry in the CCB experiment for [PITH_FULL_IMAGE:figures/full_fig_p010_3.png] view at source ↗
Figure 4
Figure 4. Figure 4: Example of a reconstructed double-track cosmic event in the two fitted projec [PITH_FULL_IMAGE:figures/full_fig_p011_4.png] view at source ↗
Figure 5
Figure 5. Figure 5: Three-dimensional view of the same reconstructed double-track cosmic event as [PITH_FULL_IMAGE:figures/full_fig_p012_5.png] view at source ↗
Figure 6
Figure 6. Figure 6: Example of two clusters reconstructed in the pad row centred at [PITH_FULL_IMAGE:figures/full_fig_p013_6.png] view at source ↗
Figure 7
Figure 7. Figure 7: Time profiles for the two clusters shown in Figure 6. The ADC values are [PITH_FULL_IMAGE:figures/full_fig_p015_7.png] view at source ↗
Figure 8
Figure 8. Figure 8: Pad-column multiplicity of reconstructed centroids. [PITH_FULL_IMAGE:figures/full_fig_p022_8.png] view at source ↗
Figure 9
Figure 9. Figure 9: Example dE/dx distributions for two GEM-voltage settings in cosmic data. The 350 V setting gives a clearer Landau-like peak, while the higher gain at 360 V broadens the distribution. 23 [PITH_FULL_IMAGE:figures/full_fig_p023_9.png] view at source ↗
Figure 10
Figure 10. Figure 10: Comparison of the reconstructed dE/dx distributions for short and long drift distances at the reference cosmic operating point, Edrift = 500 V/cm and gas flow 12 l/h. The two distributions nearly overlap, indicating stable charge collection across the drift volume used in the analysis. A detailed comparison of residual widths for the different data sets is given in Section 5. Here, one representative resi… view at source ↗
Figure 11
Figure 11. Figure 11: Representative residual distributions for tracks reconstructed at the reference [PITH_FULL_IMAGE:figures/full_fig_p026_11.png] view at source ↗
Figure 12
Figure 12. Figure 12: Track-level dE/dx distributions for the reference cosmic data set, comparing the arithmetic mean over all centroids with the truncated mean after applying the global 70th-percentile centroid-level threshold. 6.1. ADC time-profile response The dependence of the observed pulse shape on detector settings was stud￾ied using cosmic measurements. Examples are shown in [PITH_FULL_IMAGE:figures/full_fig_p027_12.png] view at source ↗
Figure 13
Figure 13. Figure 13: Representative central-pad-column time profiles from reconstructed clusters in [PITH_FULL_IMAGE:figures/full_fig_p028_13.png] view at source ↗
Figure 14
Figure 14. Figure 14: Centroid-normalised dE/dx distributions for trigger tracks and background tracks in the analysed CCB data set. Trigger tracks are defined as tracks whose projection to the TPC face falls inside the geometrical window defined by the trigger scintillators. Background tracks are reconstructed outside this window. The reconstructed dE/dx is used as a quantity proportional to the charge deposited per unit trac… view at source ↗
Figure 15
Figure 15. Figure 15: Representative central-pad-column time profiles from reconstructed clusters in [PITH_FULL_IMAGE:figures/full_fig_p031_15.png] view at source ↗
Figure 16
Figure 16. Figure 16: Comparison of summed cluster time profiles in neighbouring pad rows for rep [PITH_FULL_IMAGE:figures/full_fig_p032_16.png] view at source ↗
Figure 17
Figure 17. Figure 17: Example of an inclined CCB track before and after the sub-centroid refit. [PITH_FULL_IMAGE:figures/full_fig_p033_17.png] view at source ↗
read the original abstract

A compact time projection chamber (TPC) prototype was studied for charged-pion tracking in the annihilation detector proposed for the HIBEAM experiment at the European Spallation Source. HIBEAM aims to search for neutron-antineutron oscillations, where a produced antineutron would annihilate on a carbon target and produce a pionic final state. A tracking algorithm was developed and validated using cosmic-particle measurements expected to be dominated by atmospheric cosmic muons, proton elastic-scattering data from the Cyclotron Centre Bronowice, and simulated TPC event data. Cosmic measurements provided a minimum-ionising reference for pion-like tracks, while proton-scattering data tested reconstruction in a more highly ionising environment. Simulated crossing-track events were used as a stress test of complex topologies. The algorithm performed reliably for well-separated tracks, while crossing or overlapping tracks and dense proton-scattering events reduced performance. In experimental data, reconstructed tracks showed sub-millimetre residual widths, robust charge sharing supporting the zigzag-shaped readout, and uniform measured dE/dx across the drift volume. The truncated-mean track-level dE/dx distribution in cosmic data showed an approximately Gaussian peak with a relative width of about 16%, demonstrating how energy-loss information can be used for particle identification. Tilted proton tracks showed broader residuals in yz, because the pad row signal was extended in time. A sub-centroid refit technique was proposed, using the internal ADC time profile within a pad row instead of a single charge-weighted time position. With four equal-y sub-centroids per pad row, the yz residual width was reduced from 1.30 mm to 0.55 mm. These results validate the initial tracking capabilities of the algorithm and prototype, and provide feedback for the next-generation prototype.

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 presents the development and characterization of a compact time projection chamber (TPC) prototype for charged-pion tracking in the annihilation detector proposed for the HIBEAM experiment at the European Spallation Source. The work focuses on a tracking algorithm validated with cosmic-particle data (treated as a minimum-ionizing reference), proton elastic-scattering data from the Cyclotron Centre Bronowice, and simulated TPC events. Reported outcomes include an approximately Gaussian truncated-mean dE/dx distribution with ~16% relative width in cosmic data, sub-millimeter position residuals, and a reduction in yz residual width from 1.30 mm to 0.55 mm via a sub-centroid refit using internal ADC time profiles.

Significance. If the performance metrics hold, the prototype validation provides concrete experimental support for the tracking and dE/dx capabilities required in the HIBEAM n-nbar oscillation search. The sub-centroid refit technique offers a practical method for improving resolution on tilted tracks, and the multi-source validation (cosmic, proton, simulation) adds robustness to the claims of reliable performance for well-separated tracks.

major comments (2)
  1. [Abstract] Abstract (validation data sources paragraph): Details on data selection criteria, error propagation, and quantitative metrics for the comparison between experimental data and simulated crossing-track events are not provided. These are needed to assess the robustness of the quoted performance figures, including the 16% dE/dx width and the residual improvement from 1.30 mm to 0.55 mm.
  2. [Abstract] Abstract (paragraph on validation data sources): The assumption that cosmic measurements are dominated by atmospheric muons serving as an MIP reference for the expected pionic final states is stated explicitly but lacks supporting quantitative justification or references within the manuscript; while conventional, this link is relevant to the physics motivation.
minor comments (2)
  1. [Abstract] The manuscript would benefit from a summary table collating key performance metrics (dE/dx width, residuals) across the three validation datasets for easier comparison.
  2. [Abstract] Clarify the exact definition and implementation of the 'truncated-mean' dE/dx calculation and the 'sub-centroid refit' (e.g., how the four equal-y sub-centroids are determined and combined).

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the constructive comments and positive recommendation. We address the two major comments on the abstract below and will incorporate revisions to strengthen the presentation of validation details.

read point-by-point responses

  1. Referee: [Abstract] Abstract (validation data sources paragraph): Details on data selection criteria, error propagation, and quantitative metrics for the comparison between experimental data and simulated crossing-track events are not provided. These are needed to assess the robustness of the quoted performance figures, including the 16% dE/dx width and the residual improvement from 1.30 mm to 0.55 mm.

    Authors: The abstract is intentionally concise, with detailed descriptions of data selection, error propagation, and quantitative comparisons (including direct experimental-simulation metrics for crossing tracks) provided in the dedicated analysis and results sections of the manuscript. To improve accessibility, we will revise the abstract paragraph to include one additional sentence summarizing the key selection criteria and the reported residual/dE/dx metrics with their uncertainties, while retaining brevity. revision: yes

  2. Referee: [Abstract] Abstract (paragraph on validation data sources): The assumption that cosmic measurements are dominated by atmospheric muons serving as an MIP reference for the expected pionic final states is stated explicitly but lacks supporting quantitative justification or references within the manuscript; while conventional, this link is relevant to the physics motivation.

    Authors: We agree that an explicit reference or brief quantitative note would strengthen the justification. We will add a short clause with a standard reference to sea-level cosmic muon flux and composition (e.g., PDG or equivalent) to support the MIP reference assumption in the revised abstract. revision: yes

Circularity Check

0 steps flagged

No significant circularity; experimental measurements are self-contained

full rationale

The paper reports direct experimental outcomes from cosmic-particle and proton-scattering data, including measured residual widths (1.30 mm to 0.55 mm after refit) and dE/dx relative width (~16%), validated against independent simulations and external data sources. No load-bearing step invokes an equation, fit, or self-citation that reduces the reported quantities to inputs defined from the same dataset; the cosmic-muon reference assumption is stated as a conventional expectation without internal derivation. The work contains no mathematical prediction chain or ansatz smuggling, rendering it self-contained against external benchmarks.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

The paper is an experimental instrumentation study with no new theoretical parameters, axioms, or postulated entities introduced.

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Works this paper leans on

26 extracted references · 15 canonical work pages · 1 internal anchor

  1. [1]

    Santoro, D

    V. Santoro, D. Milstead, P. Fierlinger, W. Snow, J. Amaral, J. Barrow, M. Bartis, P. Bentley, L. Björk, G. Brooijmans, et al., The hibeam instrument at the european spallation source, Journal of Physics G: Nuclear and Particle Physics 52 (4) (2025) 040501

    2025

  2. [2]

    Addazi, K

    A. Addazi, K. Anderson, S. Ansell, K. Babu, J. Barrow, D. Baxter, P. Bentley, Z. Berezhiani, R. Bevilacqua, R. Biondi, et al., New high- sensitivity searches for neutrons converting into antineutrons and/or sterile neutrons at the hibeam/nnbar experiment at the european spal- lation source, Journal of Physics G: Nuclear and Particle Physics 48 (7) (2021) 070501

    2021

  3. [3]

    Santoro, et al., HighNESS conceptual design report: Volume II

    V. Santoro, et al., HighNESS conceptual design report: Volume II. The NNBAR experiment., J. Neutron Res. 25 (3-4) (2024) 315–406. doi:10.3233/jnr-230951

    work page doi:10.3233/jnr-230951 2024

  4. [4]

    Garoby, A

    R. Garoby, A. Vergara, H. Danared, I. Alonso, E. Bargallo, B. Chey- mol, C. Darve, M. Eshraqi, H. Hassanzadegan, A. Jansson, et al., The european spallation source design, Physica Scripta 93 (1) (2017) 014001

    2017

  5. [5]

    A. D. Sakharov, Violation of CP invariance, C asymmetry, and baryon asymmetry of the Universe, Pisma Zh. Eksp. Teor. Fiz. 5 (1967) 32–35. doi:10.1070/PU1991v034n05ABEH002497

    work page doi:10.1070/pu1991v034n05abeh002497 1967

  6. [6]

    Baldo-Ceolin, P

    M. Baldo-Ceolin, P. Benetti, T. Bitter, F. Bobisut, E. Calligarich, R. Dolfini, D. Dubbers, P. El-Muzeini, M. Genoni, D. Gibin, et al., A new experimental limit on neutron-antineutron oscillations, Zeitschrift für Physik C Particles and Fields 63 (3) (1994) 409–416

    1994

  7. [7]

    C. B. Dover, A. Gal, J. M. Richard, Neutron antineu- tron oscillations in nuclei, Phys. Rev. D27 (1983) 1090–1100. doi:10.1103/PhysRevD.27.1090

    work page doi:10.1103/physrevd.27.1090 1983

  8. [8]

    J. L. Barrow, P. Fierlinger, Y. Kamyshkov, B. Meirose, D. Milstead, R. N. Mohapatra, V. Santoro, Avoiding Blindness in Baryon Number Violating Processes: Free-Beam and Intranuclear Paths to Neutron- Antineutron Transitions (11 2025). arXiv:2511.01829. 40

    work page arXiv 2025

  9. [9]

    J. N. Marx, D. R. Nygren, The time projection chamber, Physics Today 31 (10) (1978) 46–53

    1978

  10. [10]

    J. Alme, Y. Andres, H. Appelshäuser, S. Bablok, N. Bialas, R. Bolgen, U. Bonnes, R. Bramm, P. Braun-Munzinger, R. Campagnolo, et al., The alice tpc, a large 3-dimensional tracking device with fast readout for ultra-high multiplicity events, Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated...

    2010

  11. [11]

    Ivanov, I

    M. Ivanov, I. Belikov, P. Hristov, K. Šafařík, Track reconstruction in high density environment, Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associ- ated Equipment 566 (1) (2006) 70–74

    2006

  12. [12]

    E. S. Golubeva, L. A. Kondratyuk, Annihilation of low energy an- tineutrons on nuclei, Nucl. Phys. B Proc. Suppl. 56 (1997) 103–107. doi:10.1016/S0920-5632(97)00260-0

    work page doi:10.1016/s0920-5632(97)00260-0 1997

  13. [13]

    E. S. Golubeva, J. L. Barrow, C. G. Ladd, Model of¯nannihilation in experimental searches for¯ntransformations, Phys. Rev. D 99 (3) (2019) 035002. arXiv:1804.10270, doi:10.1103/PhysRevD.99.035002

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.1103/physrevd.99.035002 2019

  14. [14]

    J. L. Barrow, E. S. Golubeva, E. Paryev, J.-M. Richard, Progress and simulations for intranuclear neutron-antineutron transformations in 40 18Ar, Phys. Rev. D 101 (3) (2020) 036008. arXiv:1906.02833, doi:10.1103/PhysRevD.101.036008

    work page doi:10.1103/physrevd.101.036008 2020

  15. [15]

    Abe, et al., Search for neutron-antineutron oscillation in super-kamiokande, Physical Review D 91 (7) (2015) 072006

    K. Abe, et al., Search for neutron-antineutron oscillation in super-kamiokande, Physical Review D 91 (7) (2015) 072006. doi:10.1103/PhysRevD.91.072006

    work page doi:10.1103/physrevd.91.072006 2015

  16. [16]

    M. B. L. Persson, Design of an experiment to search for neutron oscil- lations at the european spallation source (2024)

    2024

  17. [17]

    Hehl, Characterization of the hibeam time projection chamber proto- type, bachelor project, Division of Particle and Nuclear Physics (2025)

    V. Hehl, Characterization of the hibeam time projection chamber proto- type, bachelor project, Division of Particle and Nuclear Physics (2025). URLhttp://lup.lub.lu.se/student-papers/record/9203174 41

    work page arXiv 2025

  18. [18]

    Sauli, Gem: A new concept for electron amplification in gas detectors, Nuclear Instruments and Methods in Physics Research Section A 386 (2–

    F. Sauli, Gem: A new concept for electron amplification in gas detectors, Nuclear Instruments and Methods in Physics Research Section A 386 (2–

  19. [19]

    doi:10.1016/S0168-9002(96)01172-2

    (1997) 531–534. doi:10.1016/S0168-9002(96)01172-2

    work page doi:10.1016/s0168-9002(96)01172-2 1997

  20. [20]

    Shoji, Measurement of de/dx resolution of tpc prototype with gating gem exposed to an electron beam, in: Proceedings of the International Workshop on Future Linear Colliders, 2018

    A. Shoji, Measurement of de/dx resolution of tpc prototype with gating gem exposed to an electron beam, in: Proceedings of the International Workshop on Future Linear Colliders, 2018

    2018

  21. [21]

    Aspell, M

    P. Aspell, M. DeGaspari, H. França, E. García, L. Musa, Super-altro 16: A front-end system on chip for dsp based readout of gaseous de- tectors, IEEE Transactions on Nuclear Science 60 (2013) 1289–1295. doi:10.1109/TNS.2013.2250305

    work page doi:10.1109/tns.2013.2250305 2013

  22. [22]

    M. D. Gaspari, Systems-on-Chip (SoC) for applications in High-Energy Physics, Doctoral dissertation, Ruprecht-Karls-Universität Heidelberg (2012). doi:10.11588/heidok.00013806

    work page doi:10.11588/heidok.00013806 2012

  23. [23]

    Martoiu, H

    S. Martoiu, H. Muller, A. Tarazona, J. Toledo, Development of the scalable readout system for micro-pattern gas detectors and other applications, Journal of Instrumentation 8 (03) (2013) C03015. doi:10.1088/1748-0221/8/03/C03015

    work page doi:10.1088/1748-0221/8/03/c03015 2013

  24. [24]

    R. L. Workman, et al., Review of particle physics, Progress of Theoretical and Experimental Physics 2022 (8) (2022) 083C01. doi:10.1093/ptep/ptac097

    work page doi:10.1093/ptep/ptac097 2022

  25. [25]

    Tanabashi, et al., Passage of particles through matter, in: Review of Particle Physics, Vol

    M. Tanabashi, et al., Passage of particles through matter, in: Review of Particle Physics, Vol. 98, 2018, p. 030001, updated in subsequent editions of the PDG Review

    2018

  26. [26]

    H. W. Kuhn, The hungarian method for the assignment prob- lem, Naval Research Logistics Quarterly 2 (1-2) (1955) 83–97. doi:10.1002/nav.3800020109. 42

    work page doi:10.1002/nav.3800020109 1955