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arxiv: 2606.26856 · v1 · pith:BY646ZFOnew · submitted 2026-06-25 · ✦ hep-ex

Calibration and Performance of proANUBIS: A proof-of-concept detector for the ANUBIS experiment

Giulio Aielli , Oleg Brandt , Jude Burling , Patrick Collins , Jonas Dej , Cayetano Fernandez Ruiz , Christopher Lester , Kaijia Liu
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Luca Pizzimento Ludovico Pontecorvo Theo Reymermier Michael Revering Aashaq Shah Tom Spencer Paul Swallow (for the ANUBIS Collaboration)
This is my paper

Pith reviewed 2026-06-26 01:53 UTC · model grok-4.3

classification ✦ hep-ex
keywords long-lived particlesResistive Plate ChambersANUBISATLASdetector calibrationperformance validationLHC collisions
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The pith

The proANUBIS prototype detector achieves the efficiency and timing resolution required for the ANUBIS long-lived particle search.

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

The ANUBIS experiment aims to detect long-lived particles by instrumenting the ATLAS cavern ceiling with Resistive Plate Chambers to find their decays in the air above the detector. proANUBIS is a smaller proof-of-concept version placed in the same environment to test the technology with actual LHC proton-proton collision data. The paper analyzes the collected data to measure muon and hadron fluxes and evaluates the detector's performance. It concludes that the efficiency and timing resolution align with expectations and satisfy the needs for the full-scale ANUBIS setup.

Core claim

The proANUBIS detector was installed in the ATLAS cavern and operated with pp collision data from the LHC. Reconstruction techniques were applied to identify particles, and the detection efficiency and timing resolution were measured to be consistent with expectations from simulations and prior tests, thereby meeting the performance requirements specified for the ANUBIS experiment.

What carries the argument

The proANUBIS detector, an array of Resistive Plate Chambers (RPCs) that record the passage of charged particles to allow reconstruction of decay vertices in the cavern volume.

If this is right

  • Scaling the proANUBIS design to the full ANUBIS coverage will provide the necessary sensitivity to long-lived particles with lifetimes greater than 10 ps.
  • In-situ flux measurements can be used to refine background models for the full experiment.
  • The validation reduces the risk associated with deploying a large detector in the cavern environment.

Where Pith is reading between the lines

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

  • Successful operation in the cavern suggests that RPC technology can handle the radiation and magnetic field conditions present there.
  • This proof-of-concept could encourage similar ceiling-mounted detectors in other experiments for LLP searches.
  • The data collected might allow studies of cosmic ray or beam-related backgrounds not previously measured in that location.

Load-bearing premise

The conditions experienced by proANUBIS during the data collection period accurately reflect those that the full ANUBIS detector will encounter.

What would settle it

A direct comparison showing that the timing resolution worsens beyond acceptable limits when the detector is scaled to the full ANUBIS size or relocated to a different position in the cavern.

Figures

Figures reproduced from arXiv: 2606.26856 by Aashaq Shah, Cayetano Fernandez Ruiz, Christopher Lester, Giulio Aielli, Jonas Dej, Jude Burling, Kaijia Liu, Luca Pizzimento, Ludovico Pontecorvo, Michael Revering, Oleg Brandt, Patrick Collins, Paul Swallow (for the ANUBIS Collaboration), Theo Reymermier, Tom Spencer.

Figure 1
Figure 1. Figure 1 [PITH_FULL_IMAGE:figures/full_fig_p002_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: The location of the proANUBIS detector (yellow) within the ATLAS cavern. tem requiring coincident hits across a configurable number of η RPC planes within a 60 ns coincidence window. Due to the high hit detection efficiency of > 95% the ϕ RPC planes are not used in the trigger decision. When a trigger is fired, Time-to-Digital Converters (TDCs) record, for each strip, the times at which the input signal cr… view at source ↗
Figure 4
Figure 4. Figure 4: The number of η RPC planes that recorded hits per event during LHC collisions with the original DAQ system in an example 2024 run compared to the upgraded DAQ for an example 2025 run with similar data-taking conditions. proceeds through several stages. First, hits are filtered to sup￾press electronic noise, after which they are grouped into one￾dimensional (1D) clusters independently in the η and ϕ read￾ou… view at source ↗
Figure 3
Figure 3. Figure 3: The trigger rate in proANUBIS and the ATLAS instantaneous lu￾minosity in pp collisions at √ s = 13.6 TeV for Run 474926 as a function of British Summer Time (BST). During the year-end technical stop at the end of 2024, the proANUBIS data acquisition (DAQ) system was upgraded, replacing the CAEN V767 TDCs with the higher-resolution model CAEN V1190 A, improving the instrumental time reso￾lution from 800 ps … view at source ↗
Figure 5
Figure 5. Figure 5: The 1D cluster size in the η and ϕ planes in pp collisions in 2025 data. 5300 5350 5400 5450 5500 5550 5600 5650 5700 5750 RPC Voltage [V] 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 Average Cluster Size [strips] pp collisions, 2025 data p s = 13.6 TeV, 0.82 fb 1 ATLAS Run 503886 planes planes [PITH_FULL_IMAGE:figures/full_fig_p004_5.png] view at source ↗
Figure 7
Figure 7. Figure 7: The number of 2D clusters per event for a sample of cosmic ray data and pp collision data collected on the same day. 4.2. Track Fitting The clusters are combined to form tracks using a three￾stage process. First, track ‘seeds’ are constructed independently within each tracking layer. These seeds are then paired across different layers to identify candidate tracks spanning the detec￾tor volume. Finally, the… view at source ↗
Figure 8
Figure 8. Figure 8: A proANUBIS event display for a single-track event in pp collisions. A display of representative proANUBIS event with two re￾constructed tracks collected in pp collisions is shown in Fig￾ure 9. In this event, the pairing requirements used in the clus￾ter formation consistently select the same corners in each RPC plane, and two tracks are reconstructed. The direction and ve￾locities of both tracks are consi… view at source ↗
Figure 11
Figure 11. Figure 11: The RPC hit efficiency in the Triplet Top plane as a function of the X and Y position of the projected track, with the low-efficiency regions outlined by a dotted white line. The resulting 1D cluster efficiencies of each RPC in proANUBIS are shown as a function of the applied HV, sep￾arately for the η and ϕ readout strips in [PITH_FULL_IMAGE:figures/full_fig_p006_11.png] view at source ↗
Figure 10
Figure 10. Figure 10: The distance between projected track position and the nearest 2D cluster in three example RPC planes. The threshold for associating the 2D cluster with a track for the purpose of the efficiency measurement is indicated by the dotted vertical line. To account for inactive strips or localised regions on the RPC with a systematically lower efficiency, the RPC efficiency is first measured as a function of the… view at source ↗
Figure 12
Figure 12. Figure 12: The RPC efficiency measured in cosmic ray data as a function of applied HV to the RPC plane under study. The efficiency of the η plane is shown in panel (a), and the ϕ plane in panel (b). 1.5 1.6 1.7 1.8 1.9 2.0 Threshold Voltage [V] 0.5 0.6 0.7 0.8 0.9 1.0 Hit Efficiency planes Cosmic ray data 2025 Triplet Low Triplet Mid Triplet Top Singlet Doublet Low Doublet Top [PITH_FULL_IMAGE:figures/full_fig_p007… view at source ↗
Figure 13
Figure 13. Figure 13: The RPC hit efficiency in all ϕ planes as a function of the applied threshold voltage. the front-end (FE) electronics, introducing a ϕ-dependent delay to the registered η hit times and an η-dependent delay to the ϕ hit times. This signal propagation speed is determined using a combined fit of the average η - ϕ time difference for all pairwise combinations of strips in each plane. Only those events where t… view at source ↗
Figure 14
Figure 14. Figure 14: ToA differences for each pairwise combination of η and ϕ channels in the Triplet Top layer with the signal propagation time and overall η − ϕ scale removed. The white cells correspond to η - ϕ ToA differences that have no entries or are outside of the [−2, 2] ns time window. 0 20 40 60 Channel 0 5 10 15 20 25 30 C h a n n el proANUBIS, Triplet Top plane Post-calibration pp collisions, 2025 Data p s = 13.6… view at source ↗
Figure 16
Figure 16. Figure 16: Observed time-of-flight for RPC planes with adjacent indices, rela￾tive to the expected time difference for tracks with β = 1. 6.3. Time Walk An additional correction is applied to the ToA of each hit due to the correlation between ToA and TOT in the RPC read￾out strips. The ToA is measured as the time when the input voltage surpasses the threshold voltage. Therefore, larger sig￾nals with identical truth … view at source ↗
Figure 19
Figure 19. Figure 19: The ToF difference relative to expectation in the Doublet RPC layer before and after applying the TOT calibration. planes, its uncertainty is proportional to the quadratic sum of the uncertainties on the hit times in those planes. To extract the resolution of each individual plane, the width of the time differ￾ence is found for all three pair-wise combinations of the planes in the Triplet layer and the re… view at source ↗
Figure 17
Figure 17. Figure 17: The distribution of the number of tracks as a function of the ToF between the two Doublet planes, and the Doublet Low TOT. Also shown is the centre of the fit at each TOT (black solid line). 5 10 15 20 25 30 Doublet Top TOT [ns] 3 2 1 0 1 2 3 Doublet ToF - F(TOT0) [ns] pp collisions p s = 13.6 TeV, 0.4 fb 1 2025 data, ATLAS Run 499666 Gaussian fit center 10 0 10 1 10 2 Tracks [PITH_FULL_IMAGE:figures/ful… view at source ↗
Figure 18
Figure 18. Figure 18: The distribution of the number of tracks as a function of the ToF between the two Doublet planes after correcting for F(TOT0), and the Doublet Top TOT. Here, F(TOT0) represents the calibration applied using the lower Doublet TOT. Also shown is the centre of the fit at each TOT (black solid line). 7. Time Resolution With the full set of calibrations applied, the proANUBIS time resolution is determined by c… view at source ↗
Figure 20
Figure 20. Figure 20: Observed ToF relative to ToF for tracks with β = 1 for all combina￾tions of RPC planes in the Triplet layer. 5.3 5.4 5.5 5.6 5.7 5.8 HV [kV] 0.36 0.38 0.40 0.42 0.44 0.46 0.48 Time Resolution [ns] pp collisions p s = 13.6 TeV, 0.82 fb 1 2025 data, ATLAS Run 503886 Triplet Low Triplet Mid [PITH_FULL_IMAGE:figures/full_fig_p010_20.png] view at source ↗
Figure 21
Figure 21. Figure 21: Measured time resolution for the Triplet Mid and Low planes as a function of the high voltage applied. non-uniformities in the surface of the RPC gas gaps, or correla￾tions in the track angle and position in the detector. These vari￾ations are seen to be stable over month timescales, indicating that the time resolution could potentially be improved through more sophisticated calibration. 8. Summary and ou… view at source ↗
read the original abstract

Long-lived particles with lifetimes $\tau>10$~ps are predicted by many extensions of the Standard Model with viable dark matter candidates. The ANUBIS experiment proposes to extend the experimental sensitivity to long-lived particles by instrumenting the ceiling of the ATLAS cavern with Resistive Plate Chamber detectors in order to reconstruct vertices from long-lived particle decays in the air-filled volume above the ATLAS detector. The proANUBIS detector has been installed in the ATLAS cavern to validate the detector technology planned for ANUBIS and to take in-situ measurements of muon and hadron fluxes inside the ATLAS cavern using $pp$ collision data from the LHC. In this paper, the data collected, reconstruction techniques used, and performance of the \proanubis detector are discussed. The detection efficiency and timing resolution are found to be consistent with expectations and to meet the performance requirements of ANUBIS.

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 describes the proANUBIS detector, a proof-of-concept Resistive Plate Chamber array installed in the ATLAS cavern to validate technology for the ANUBIS experiment. Using in-situ data from pp collisions, it discusses data collection, reconstruction techniques, and reports that the measured detection efficiency and timing resolution are consistent with expectations and satisfy ANUBIS performance requirements.

Significance. If the quantitative performance metrics hold, this provides essential validation of the RPC technology and cavern particle environment for ANUBIS, supporting its goal of extending sensitivity to long-lived particles. The in-situ flux measurements represent a concrete strength for assessing real-world conditions.

major comments (1)
  1. [Abstract] Abstract: the central claim that 'the detection efficiency and timing resolution are found to be consistent with expectations' supplies no quantitative measured values, uncertainties, data selection criteria, or comparison plots, so the claim cannot be evaluated from the provided information.

Simulated Author's Rebuttal

1 responses · 0 unresolved

We thank the referee for their comments on our manuscript. We address the point raised regarding the abstract below.

read point-by-point responses

  1. Referee: [Abstract] Abstract: the central claim that 'the detection efficiency and timing resolution are found to be consistent with expectations' supplies no quantitative measured values, uncertainties, data selection criteria, or comparison plots, so the claim cannot be evaluated from the provided information.

    Authors: We agree that the abstract, as currently written, does not include the specific quantitative results, uncertainties, or references to data selection and figures that would allow a reader to evaluate the claim directly from the abstract alone. The body of the manuscript does present these details (including measured efficiencies, timing resolutions, selection criteria, and comparison plots), but the abstract should be updated to summarize them. In the revised version we will expand the abstract to include the key measured values with uncertainties and brief references to the relevant sections. revision: yes

Circularity Check

0 steps flagged

No significant circularity in experimental performance report

full rationale

This is a pure experimental calibration paper reporting in-situ measurements of detector efficiency and timing resolution from pp collision data. The central claims consist of direct comparisons of observed performance metrics to pre-existing expectations, with no equations, derivations, fitted parameters renamed as predictions, or load-bearing self-citations. The paper contains no derivation chain that could reduce to its own inputs by construction, satisfying the default expectation of no circularity for measurement reports.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

Paper is an experimental calibration report relying on standard detector physics assumptions rather than new derivations; no free parameters or invented entities are evident from the abstract.

axioms (1)
  • domain assumption Resistive Plate Chambers respond to muons and hadrons with efficiency and timing properties that can be modeled from lab and simulation data.
    Used to judge whether measured performance meets ANUBIS requirements.

pith-pipeline@v0.9.1-grok · 5741 in / 1109 out tokens · 27183 ms · 2026-06-26T01:53:29.341697+00:00 · methodology

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Reference graph

Works this paper leans on

18 extracted references · 1 canonical work pages

  1. [1]

    ANUBIS: Proposal to search for long-lived neutral particles in CERN service shafts

    M. Bauer, O. Brandt, L. Lee, and C. Ohm, “ANUBIS: Proposal to search for long-lived neutral particles in CERN service shafts”, (2019), arXiv:1909.13022 [physics.ins-det]

    arXiv 2019

  2. [2]

    The ANUBIS detector and its sensitivity to neutral long-lived particles

    ANUBIS Collaboration, “The ANUBIS detector and its sensitivity to neutral long-lived particles”, (2025), arXiv:2510.26932 [hep-ex]

    arXiv 2025

  3. [3]

    LHC Machine

    L. R. Evans and P. Bryant, “LHC Machine”, JINST3, S08001 (2008)

    2008

  4. [4]

    Searching for long-lived particles beyond the Standard Model at the Large Hadron Collider

    J. Alimena et al., “Searching for long-lived particles beyond the Standard Model at the Large Hadron Collider”, J. Phys. G47, 090501 (2020), arXiv:1903.04497 [hep-ex]

    arXiv 2020

  5. [5]

    Summary Report of the Physics Beyond Colliders Study at CERN

    R. Alemany Fern ´andez et al. (PBC Collaboration), “Summary Report of the Physics Beyond Colliders Study at CERN”, (2025), arXiv:2505.00947 [hep-ex]

    arXiv 2025

  6. [6]

    The ATLAS Experiment at the CERN Large Hadron Collider

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

    2008

  7. [7]

    The ATLAS experiment at the CERN Large Hadron Collider: a description of the detector configuration for Run 3

    ATLAS Collaboration, “The ATLAS experiment at the CERN Large Hadron Collider: a description of the detector configuration for Run 3”, JINST19, P05063 (2024), arXiv:2305.16623 [physics.ins-det]

    arXiv 2024

  8. [8]

    Development of resistive plate counters

    R. Santonico and R. Cardarelli, “Development of resistive plate counters”, Nucl. Instrum. Meth. in Phys. Res.187, 377–380 (1981). 10

    1981

  9. [9]

    Performance of the BIS78 RPC detectors: a new concept of electronics and detector integration for high-rate and fast timing large size RPCs

    L. Pizzimento (ATLAS), “Performance of the BIS78 RPC detectors: a new concept of electronics and detector integration for high-rate and fast timing large size RPCs”, JINST15, edited by B. Liberti, A. Paoloni, and P. Camarri, C11010 (2020), arXiv:2006.09722 [physics.ins-det]

    arXiv 2020

  10. [10]

    Performance of the ATLAS RPC detector and Level-1 muon barrel trigger at √s=13 TeV

    ATLAS Collaboration, “Performance of the ATLAS RPC detector and Level-1 muon barrel trigger at √s=13 TeV”, JINST16, P07029 (2021), arXiv:2103.01029 [physics.ins-det]

    arXiv 2021

  11. [11]

    Construction of proANUBIS: A proof-of-concept detector for the ANUBIS experiment

    ANUBIS Collaboration, “Construction of proANUBIS: A proof-of-concept detector for the ANUBIS experiment”, Nucl. Instrum. Meth. A1091, 171687 (2025), arXiv:2512.13926 [hep-ex]

    arXiv 2025

  12. [12]

    Commissioning of proANUBIS: A proof-of-concept detector for the ANUBIS experiment

    ANUBIS Collaboration, “Commissioning of proANUBIS: A proof-of-concept detector for the ANUBIS experiment”, Nucl. Instrum. Meth. A1089, 171501 (2026), arXiv:2512.18414 [hep-ex]

    arXiv 2026

  13. [13]

    The BIS78 Resistive Plate Chambers upgrade of the ATLAS Muon Spectrometer for the LHC Run-3

    ATLAS Muon Collaboration, “The BIS78 Resistive Plate Chambers upgrade of the ATLAS Muon Spectrometer for the LHC Run-3”, JINST15, C10026 (2020), arXiv:2004.12693 [physics.ins-det]

    arXiv 2020

  14. [14]

    Performance and longevity of ATLAS RPCs with new lower GWP mixtures

    S. Simsek, “Performance and longevity of ATLAS RPCs with new lower GWP mixtures”, Nucl. Instrum. Meth. A1079, 170618 (2025)

    2025

  15. [15]

    Timing, trigger and control interface module for ATLAS SCT read-out electronics

    J. Butterworth, D. Hayes, J. Lane, and M. Postranecky, “Timing, trigger and control interface module for ATLAS SCT read-out electronics”, 10.5170/CERN-1999-009.336(1999)

    work page doi:10.5170/cern-1999-009.336(1999 1999

  16. [16]

    TTC Interface Module for ATLAS Read-Out Electronics: Final production version based on Xilinx FPGA devices

    J. Butterworth, J. B. Lane, M. Postranecky, and M. R. M. Warren, “TTC Interface Module for ATLAS Read-Out Electronics: Final production version based on Xilinx FPGA devices”, ATL-ELEC-PUB-2007-004, ATL-COM-ELEC-2005-001 (2004)

    2007

  17. [17]

    Searches for long-lived particles with the ANUBIS experiment

    A. Shah (ANUBIS), “Searches for long-lived particles with the ANUBIS experiment”, PoSEPS-HEP2023, 051 (2024), arXiv:2401.11604 [hep-ex]

    arXiv 2024

  18. [18]

    Singular value decomposition and least squares solutions

    G. H. Golub and C. Reinsch, “Singular value decomposition and least squares solutions”, Num. Math.14, 403–420 (1970). 11

    1970