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arxiv: 2606.30150 · v1 · pith:LNUZYH5Lnew · submitted 2026-06-29 · ⚛️ physics.ins-det

Charge sharing and alignment performance of bent ALPIDEs measured with low-energy protons

Berkin Ulukutlu , Christopher Ehrich , Laura Fabbietti , Roman Gernh\"auser , Fabrizio Grosa , Hartmut Hillemanns , Tobias Jenegger , Alex Kluge
show 9 more authors
Lukas Lautner Magnus Mager Lukas Ponnath Andrea Rossi Isabella Sannaa Serhiy Senyukov Johanna Stachele Miljenko \v{S}ulji\'c Laszlo Vargaa Alperen Y\"unc\"u
This is my paper

Pith reviewed 2026-06-30 03:40 UTC · model grok-4.3

classification ⚛️ physics.ins-det
keywords ALPIDEbent MAPScluster sizealignmentproton scatteringALICE ITS3CMOS sensors
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The pith

Bent ALPIDE chips show no change in cluster size from curvature and reach simulated resolutions in low-energy proton tests.

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

The study tests ALPIDE CMOS sensors bent to radii of 18 mm, 24 mm and 30 mm using 80 MeV, 120 MeV and 200 MeV protons scattered elastically from a polypropylene fiber. Cluster sizes in high-energy-loss events remain statistically unchanged compared with expectations for flat sensors. Track alignment is assessed through the distance of closest approach and the opening angle between opposing proton tracks, yielding spatial resolutions that agree with Monte Carlo predictions. These measurements serve as a proxy for the conditions expected in the curved inner layers of the ALICE ITS3 upgrade.

Core claim

Bending the ALPIDE sensors produces no measurable effect on cluster size distributions under the high dE/dx conditions provided by the low-momentum protons; the alignment residuals obtained from DCA and opening-angle observables match the values predicted by simulation, thereby validating the use of bent wafer-scale MAPS for future tracking systems.

What carries the argument

Cluster-size histograms and the distance-of-closest-approach plus opening-angle benchmarks extracted from two-arm proton-track reconstructions.

If this is right

  • Bending radii down to 18 mm can be adopted without redesign of the front-end electronics or clustering algorithms.
  • Existing alignment procedures developed for flat ALPIDE planes remain applicable once the sensor curvature is accounted for in the geometry model.
  • The same proton-scattering setup can serve as a calibration source for other bent MAPS prototypes.
  • Charge-sharing behavior in bent sensors is sufficiently stable to support the target position resolution of the ITS3 innermost layers.

Where Pith is reading between the lines

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

  • The absence of bending-induced cluster-size changes suggests that mechanical stress does not alter the epitaxial-layer electric-field configuration at the tested radii.
  • Similar tests with higher-momentum particles or different sensor thicknesses would further constrain any residual curvature dependence.
  • The demonstrated alignment precision supports extending the approach to full-wafer-scale bent sensors in other collider or fixed-target experiments.

Load-bearing premise

The low-momentum protons produced by elastic scattering on the polypropylene fiber reproduce the high-energy-loss and alignment conditions that will exist inside the bent ITS3 layers.

What would settle it

A statistically significant difference in measured cluster sizes between bent and flat sensors, or alignment resolutions that deviate from the simulated expectations by more than the reported uncertainties.

Figures

Figures reproduced from arXiv: 2606.30150 by Alex Kluge, Alperen Y\"unc\"u, Andrea Rossi, Berkin Ulukutlu, Christopher Ehrich, Fabrizio Grosa, Hartmut Hillemanns, Isabella Sannaa, Laszlo Vargaa, Laura Fabbietti, Lukas Lautner, Lukas Ponnath, Magnus Mager, Miljenko \v{S}ulji\'c, Roman Gernh\"auser, Serhiy Senyukov Johanna Stachele, Tobias Jenegger.

Figure 1
Figure 1. Figure 1: Photos of the detector setup. The used target fiber array (top left). [PITH_FULL_IMAGE:figures/full_fig_p002_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: Sketch depicting an example event. The proton beams of various [PITH_FULL_IMAGE:figures/full_fig_p003_2.png] view at source ↗
Figure 4
Figure 4. Figure 4: Distribution of impact angles between reconstructed tracks of interest [PITH_FULL_IMAGE:figures/full_fig_p004_4.png] view at source ↗
Figure 3
Figure 3. Figure 3: Raw cluster size distribution at 200 MeV proton energy and 100 e [PITH_FULL_IMAGE:figures/full_fig_p004_3.png] view at source ↗
Figure 5
Figure 5. Figure 5: Average cluster size distribution from tracks associated to a vertex in [PITH_FULL_IMAGE:figures/full_fig_p005_5.png] view at source ↗
Figure 7
Figure 7. Figure 7: Average cluster size as a function of the proton momentum from the [PITH_FULL_IMAGE:figures/full_fig_p006_7.png] view at source ↗
Figure 8
Figure 8. Figure 8: Example distributions of the residuals to the event plane for the di [PITH_FULL_IMAGE:figures/full_fig_p007_8.png] view at source ↗
Figure 10
Figure 10. Figure 10: The projections of the vertex distributions after alignment, (left) front-view, (middle) top-view, (right) side-view of the target array. [PITH_FULL_IMAGE:figures/full_fig_p008_10.png] view at source ↗
Figure 11
Figure 11. Figure 11: DCA distributions obtained for the final alignment, compared to [PITH_FULL_IMAGE:figures/full_fig_p008_11.png] view at source ↗
Figure 12
Figure 12. Figure 12: Opening angle from selected elastic scattering events compared to [PITH_FULL_IMAGE:figures/full_fig_p009_12.png] view at source ↗
read the original abstract

The upgrade of the ALICE experiments Inner Tracking System (ITS3) aims to replace its innermost detection layers with bent wafer-scale CMOS MAPS sensors. This study examines the performance of ALPIDE chips, currently used in the ALICE ITS2, when operated in a bent configuration under realistic experimental conditions. Proton beams with energies of 80 MeV, 120 MeV and 200 MeV were used to study proton-proton elastic scattering on a polypropylene fiber target reconstructed using two opposing arms of trackers with sensors bent to radii of 18 mm, 24 mm and 30 mm. The measured low-momentum protons provided a testbed for investigating clustering behavior in high-energy loss events, where no significant impact of bending was observed on cluster size. Additionally, alignment strategies for bent detectors were evaluated using the distance of closest approach (DCA) and opening angle between scattered proton tracks as benchmarks. The achieved resolution matches expectations from simulations, confirming the suitability of bent MAPS sensors for future high-energy and nuclear physics applications.

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

1 major / 0 minor

Summary. The manuscript reports measurements of ALPIDE sensors bent to radii of 18 mm, 24 mm and 30 mm using 80–200 MeV protons from elastic scattering on a polypropylene fiber target. It finds no significant change in cluster size due to bending for these high-dE/dx events and reports that alignment performance, benchmarked via distance of closest approach and opening angle, matches simulation expectations, concluding that bent MAPS sensors are suitable for ITS3 and similar applications.

Significance. If the central measurements hold, the work supplies direct experimental data on charge-sharing behavior and alignment in bent wafer-scale sensors under high ionization density, which is useful for nuclear-physics tracking. The significance for the ITS3 upgrade is more limited, however, because the test particles are not minimum-ionizing and the paper provides no evidence that bending-induced charge-sharing effects are independent of dE/dx.

major comments (1)
  1. [Abstract and final section] Abstract and final section: the claim that the results 'confirm the suitability of bent MAPS sensors for future high-energy and nuclear physics applications' is load-bearing for the paper's motivation yet rests on an untested extrapolation. The measurements use protons whose dE/dx is far above minimum-ionizing; no data, scaling argument, or simulation comparison is supplied to show that the observed null result on cluster size would persist for MIPs that dominate ITS3 tracking.

Simulated Author's Rebuttal

1 responses · 0 unresolved

We thank the referee for the constructive feedback. We address the single major comment below and agree that a revision to the scope of the conclusions is warranted.

read point-by-point responses

  1. Referee: [Abstract and final section] Abstract and final section: the claim that the results 'confirm the suitability of bent MAPS sensors for future high-energy and nuclear physics applications' is load-bearing for the paper's motivation yet rests on an untested extrapolation. The measurements use protons whose dE/dx is far above minimum-ionizing; no data, scaling argument, or simulation comparison is supplied to show that the observed null result on cluster size would persist for MIPs that dominate ITS3 tracking.

    Authors: We agree that the measurements were performed exclusively with 80–200 MeV protons (high dE/dx) and that no direct data, scaling argument, or MIP-specific simulation is presented to demonstrate that the null result on bending-induced cluster-size change holds for minimum-ionizing particles. The experiment was designed to study charge-sharing behavior under high ionization density, which is relevant for certain nuclear-physics use cases. Alignment performance was benchmarked against simulation and found to agree, independent of the dE/dx regime. To address the concern, we will revise the abstract and concluding section to remove the broad claim of suitability for high-energy physics applications and instead state that the results support the use of bent MAPS for tracking in high-dE/dx environments while noting that MIP-specific validation remains desirable. revision: yes

Circularity Check

0 steps flagged

No circularity in experimental measurement and simulation comparison

full rationale

This is a direct experimental study reporting measurements of cluster size, alignment metrics (DCA, opening angle), and resolution for bent ALPIDE sensors using low-energy proton beams. No derivations, equations, fitted parameters renamed as predictions, or self-citation chains are present in the provided text or abstract. Claims rest on observed data compared to external simulations, with no reduction of results to the paper's own inputs by construction. The derivation chain is self-contained.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

The central claim rests on standard assumptions in particle detection that the chosen proton scattering kinematics produce representative high dE/dx events and that simulation models of bent sensors are sufficiently accurate for comparison.

axioms (1)
  • domain assumption Proton-proton elastic scattering on polypropylene provides a suitable testbed for high-energy-loss clustering and alignment benchmarks representative of ITS3 conditions.
    Invoked to justify the use of 80-200 MeV protons as the experimental probe.

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discussion (0)

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Reference graph

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