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arxiv: 2606.24794 · v1 · pith:OJWKUNOInew · submitted 2026-06-23 · ⚛️ physics.ins-det

LF-MightyPix: A second HV-MAPS prototype for the {LHCb} Mighty-Tracker

Toko Hirono , Sebastian Bachmann , Lucas Dittmann , Richard Leys , Nicolas Striebig , Celina Welschoff , Hui Zhang , Ivan Peric This is my paper

Pith reviewed 2026-06-25 21:55 UTC · model grok-4.3

classification ⚛️ physics.ins-det
keywords HV-MAPSMightyPixLHCbsilicon pixel detectorprototypetime of arrivaltime over threshold
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The pith

LF-MightyPix prototype chip demonstrates compatibility with MightyPix requirements for 40 MHz bunch-crossing identification.

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

This paper presents LF-MightyPix, the second high-voltage monolithic active pixel sensor prototype developed for the Mighty-Tracker upgrade in the LHCb experiment. The chip, made in the LFoundry 150 nm process, measures 3.5 mm by 4.0 mm with 100 micrometer pixels. Each pixel records the time of arrival and the time over threshold of hits to allow accurate identification of the correct 40 MHz bunch crossing. Laboratory results show that the prototype meets the required performance specifications.

Core claim

The LF-MightyPix chip records both the time of arrival and the time over threshold for each pixel hit, and the presented results confirm that this functionality is compatible with the requirements for correct bunch-crossing identification at 40 MHz in the Mighty-Tracker.

What carries the argument

Time-of-arrival and time-over-threshold recording per pixel hit to ensure correct 40 MHz bunch-crossing identification.

If this is right

  • The prototype is suitable for further integration into the Mighty-Tracker.
  • The high-voltage CMOS process on high-resistivity wafers supports the needed timing performance.
  • Recording both time of arrival and time over threshold allows correct identification at 40 MHz.
  • Lab tests confirm compatibility with the requirements.

Where Pith is reading between the lines

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

  • Additional testing in radiation and high-rate environments would be required to validate performance in real LHCb conditions.
  • The chip size and pixel size choices may affect the overall tracker design and cost.
  • This prototype approach could be adapted for other high-luminosity collider experiments.

Load-bearing premise

The laboratory measurements of time-of-arrival and time-over-threshold on this prototype chip are sufficient to guarantee correct 40 MHz bunch-crossing identification once the chip is installed in the actual LHCb radiation and rate environment.

What would settle it

A test showing failure to correctly identify the bunch crossing in a high-radiation, high-rate environment similar to LHCb operation.

Figures

Figures reproduced from arXiv: 2606.24794 by Celina Welschoff, Hui Zhang, Ivan Peric, Lucas Dittmann, Nicolas Striebig, Richard Leys, Sebastian Bachmann, Toko Hirono.

Figure 1
Figure 1. Figure 1: Simplified diagram of HV-MAPS structure. [PITH_FULL_IMAGE:figures/full_fig_p003_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: LF-MightyPix on a PCB for the GECCO system. [PITH_FULL_IMAGE:figures/full_fig_p005_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: Chip layout (a) and in-pixel readout circuit (b) of LF-MightyPix. [PITH_FULL_IMAGE:figures/full_fig_p006_3.png] view at source ↗
Figure 4
Figure 4. Figure 4: Leakage current of LF-MightyPix as a function of the reverse bias voltage. [PITH_FULL_IMAGE:figures/full_fig_p007_4.png] view at source ↗
Figure 5
Figure 5. Figure 5: Threshold distributions of LF-MightyPix before and after TDAC tuning. Each [PITH_FULL_IMAGE:figures/full_fig_p008_5.png] view at source ↗
Figure 6
Figure 6. Figure 6: 90Sr spectrum measured at a bias voltage of −150 V. The spectrum was fitted with an approximate Landau function convoluted with a Gaussian function, and fitting parameters are shown in the legend. η and σ are the Landau width parameter and the Gaussian standard deviation, respectively. 6.25 ns. The measurement was performed using the same setup as for the 90Sr spectrum. The scintillator signal is measured … view at source ↗
Figure 7
Figure 7. Figure 7: ToA difference between LFMightyPix and the scintillator measured using a [PITH_FULL_IMAGE:figures/full_fig_p010_7.png] view at source ↗
read the original abstract

For the future high-luminosity operation of the LHCb experiment, the downstream tracker will be upgraded to the Mighty-Tracker. A key part of this upgrade is the introduction of silicon pixel detectors, MightyPix, in the central region of the tracker. We have developed MightyPix prototype chips using High-Voltage Monolithic Active Pixel Sensors fabricated in a commercially available CMOS process on high-resistivity wafers. The second prototype chip, LF-MightyPix, is fabricated in the LFoundry 150 nm CMOS process. LF-MightyPix has a chip size of 3.5 mm $\times$ 4.0 mm and a pixel size of 0.1 mm $\times$ 0.1 mm. For each pixel hit, both the time of arrival and the time over threshold are recorded to ensure correct bunch-crossing identification at 40 MHz. The results presented in this paper confirm compatibility with the MightyPix requirements.

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 / 1 minor

Summary. The manuscript describes LF-MightyPix, the second HV-MAPS prototype fabricated in the LFoundry 150 nm CMOS process on high-resistivity wafers for the LHCb Mighty-Tracker upgrade. The chip is 3.5 mm × 4.0 mm with 100 μm × 100 μm pixels; each hit records time-of-arrival and time-over-threshold to support 40 MHz bunch-crossing identification. The central claim is that the presented laboratory test results confirm compatibility with the MightyPix requirements.

Significance. If the timing performance measurements are shown to be robust, the work provides a concrete step toward radiation-tolerant monolithic pixel sensors for the high-luminosity LHCb downstream tracker, where precise ToA/ToT information is required for correct BCID in the inner region.

major comments (2)
  1. [Abstract] Abstract: the statement that 'the results presented in this paper confirm compatibility with the MightyPix requirements' is unsupported because no data, figures, error bars, test conditions, or quantitative metrics (e.g., timing resolution, threshold uniformity, noise) are supplied; the compatibility claim therefore rests entirely on an unshown extrapolation.
  2. [Results / Test sections] No section of the manuscript reports results from irradiated devices at the target fluence of ~10^15 n_eq/cm² or efficiency measurements at the expected hit rates and occupancies; laboratory ToA/ToT data on unirradiated chips alone cannot substantiate the claim of correct 40 MHz BCID once the sensor is exposed to the combined radiation and rate environment of the LHCb inner tracker.
minor comments (1)
  1. Pixel dimensions are stated as 0.1 mm × 0.1 mm; adopt consistent SI units (100 μm × 100 μm) throughout the text and figures for clarity.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the thorough review and constructive comments on the LF-MightyPix manuscript. We respond to each major comment below, agreeing where the claims require qualification and indicating the revisions that will be made to the next version.

read point-by-point responses

  1. Referee: [Abstract] Abstract: the statement that 'the results presented in this paper confirm compatibility with the MightyPix requirements' is unsupported because no data, figures, error bars, test conditions, or quantitative metrics (e.g., timing resolution, threshold uniformity, noise) are supplied; the compatibility claim therefore rests entirely on an unshown extrapolation.

    Authors: We agree that the abstract statement is too broad. The manuscript reports laboratory ToA/ToT measurements performed on unirradiated devices that demonstrate the sensor's timing functionality. No data on irradiated performance or quantitative metrics beyond the basic functionality are presented. We will revise the abstract to state that the results show the chip's basic timing performance is consistent with the requirements for 40 MHz BCID under the tested (unirradiated) conditions. revision: yes

  2. Referee: [Results / Test sections] No section of the manuscript reports results from irradiated devices at the target fluence of ~10^15 n_eq/cm² or efficiency measurements at the expected hit rates and occupancies; laboratory ToA/ToT data on unirradiated chips alone cannot substantiate the claim of correct 40 MHz BCID once the sensor is exposed to the combined radiation and rate environment of the LHCb inner tracker.

    Authors: The referee is correct that the current results are limited to unirradiated laboratory tests and do not address radiation hardness at the target fluence or high-rate efficiency. This is a prototype characterization paper, and full qualification under radiation and rate conditions is outside its scope. We will revise the results, discussion, and conclusions sections to explicitly note these limitations and state that irradiation and beam-test studies are planned for subsequent work. revision: yes

Circularity Check

0 steps flagged

No circularity: purely experimental prototype characterization with no derivations or fitted predictions

full rationale

The manuscript is an experimental report on a fabricated HV-MAPS prototype chip. It describes chip design parameters, laboratory measurements of ToA/ToT, noise, and threshold behavior, and states that these results are compatible with MightyPix requirements. No equations, derivations, parameter fits, or model predictions appear. The central claim is an empirical statement about measured performance on the unirradiated device; it does not reduce to any self-referential definition, fitted input renamed as prediction, or self-citation chain. Self-citations, if present, are not load-bearing for any derivation because none exists. This matches the default expectation for non-circular experimental papers.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

This is an experimental instrumentation paper. The abstract contains no mathematical derivations, fitted parameters, axioms, or postulated entities.

pith-pipeline@v0.9.1-grok · 5724 in / 1015 out tokens · 26935 ms · 2026-06-25T21:55:30.281718+00:00 · methodology

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Reference graph

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