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arxiv: 2606.03466 · v1 · pith:VVD4TSI4new · submitted 2026-06-02 · ✦ hep-ex

On the Charged Fragments Tagging in the ATLAS Detector during the 2025 Oxygen Campaign

Weronika Sobien , Maciej Trzebinski This is my paper

Pith reviewed 2026-06-28 07:58 UTC · model grok-4.3

classification ✦ hep-ex
keywords ATLASAFPLHCoxygen campaigncharged fragmentsion collisionsforward detectors
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The pith

AFP detectors in ATLAS tag charged fragments during 2025 oxygen-ion collisions at the LHC.

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

The paper reports on the use of ATLAS Forward Proton detectors during the 2025 LHC campaign with proton-oxygen, oxygen-oxygen, and neon-neon collisions. Inserting these detectors allows tagging of scattered charged fragments from the ion interactions. Several analysis ideas are presented along with preliminary studies showing potential signals visible in the AFP data. This approach provides a way to study ion collisions with tagged fragments on both the proton and ion sides.

Core claim

The insertion of AFP detectors on both sides during the 2025 oxygen campaign enables the tagging of scattered fragments in the recorded data, as demonstrated by preliminary studies of what could be visible in the AFP.

What carries the argument

The ATLAS Forward Proton (AFP) detectors inserted on proton and ion sides to tag charged fragments.

If this is right

  • Many interesting studies become accessible with scattered fragments being tagged.
  • Preliminary studies indicate what signals could be visible in the AFP during these collisions.
  • Analysis ideas for proton-oxygen and oxygen-oxygen collisions are outlined.

Where Pith is reading between the lines

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

  • Similar tagging could be applied to other ion species or future runs for broader studies of nuclear interactions.
  • Combining AFP data with central ATLAS detectors might allow more complete event reconstruction in ion collisions.

Load-bearing premise

The AFP detectors can effectively detect and tag the charged fragments produced in these specific ion collisions as described in the preliminary studies.

What would settle it

Observation of no charged fragment signals or tagging rates significantly below expectations in the actual 2025 AFP data would falsify the claim.

Figures

Figures reproduced from arXiv: 2606.03466 by Maciej Trzebinski, Weronika Sobien.

Figure 1
Figure 1. Figure 1: Feynman diagram of non-diffractive (left) and diffractive (right) proton￾oxygen interaction. Using only the central ATLAS detector, the discrimination between these interaction classes is limited, as their signatures can appear similar in the central region. The inclusion of forward proton detectors gives a powerful handle by providing direct information about scattered proton. The proton transport to the … view at source ↗
Figure 2
Figure 2. Figure 2: Left: proton trajectories between ATLAS collision point and forward proton detectors. Various dotted and dashed lines represent situation in which proton lost a certain portion of its initial energy, ξ = 1−Eproton/Ebeam. Particles significantly diverging from the beam are stopped by the collimators: TCL4 and TCL5. Right: diffractive pattern registered in AFP station C NEAR SiT plane 0 on proton side during… view at source ↗
Figure 4
Figure 4. Figure 4: In contrast to the proton side, the ion side exhibits a more complex [PITH_FULL_IMAGE:figures/full_fig_p004_4.png] view at source ↗
Figure 3
Figure 3. Figure 3: Left: trajectories of various ions between ATLAS collision point and for￾ward proton detectors. The two black vertical lines indicate the locations of the AFP NEAR and FAR station, respectively. Trajectories for 2H, 4He, 6Li, 10B and 16O lie on top of each other. The 97 mm shift around z = 80 m reflects transition from a single beampipe present around ATLAS to two separated ones. Right: hit positions 205 m… view at source ↗
Figure 4
Figure 4. Figure 4: Hitmaps registered by the AFP detectors during proton-oxygen ( [PITH_FULL_IMAGE:figures/full_fig_p005_4.png] view at source ↗
read the original abstract

During the Summer of 2025 the LHC collided protons with oxygen, oxygen with oxygen and neon with neon. The ATLAS experiment recorded these data with its Forward Proton detectors (AFP) inserted on both: the proton and ion sides. This allows access to many interesting studies with scattered fragments being tagged. A few analysis ideas are presented followed by preliminary studies of what could be visible in the AFP.

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 the use of ATLAS Forward Proton (AFP) detectors inserted during the 2025 LHC oxygen campaign for p-O, O-O, and Ne-Ne collisions. It claims this configuration enables tagging of scattered charged fragments and thereby grants access to multiple physics studies; a short list of analysis ideas is followed by a reference to unspecified preliminary visibility studies in the AFP.

Significance. If the feasibility of fragment tagging were quantitatively demonstrated, the work could open a new experimental channel for studying nuclear fragmentation and structure in light-ion collisions by repurposing existing forward-proton infrastructure. The current text, however, supplies only conceptual statements without supporting metrics, so its potential impact remains unrealized.

major comments (2)
  1. [preliminary studies] The section following the analysis ideas (referred to as 'preliminary studies of what could be visible in the AFP') asserts that visibility studies have been performed yet contains no efficiency curves, acceptance calculations, resolution estimates, or background-rejection figures as a function of fragment charge, Z/A ratio, or rapidity. This absence is load-bearing for the central claim that AFP tagging is effective for the relevant nuclear fragments.
  2. [introduction / abstract] No quantitative assessment is given of how the AFP acceptance, timing resolution, or tracking performance (originally tuned for forward protons in pp running) translates to the kinematics and charge states of nuclear fragments in p-O, O-O, or Ne-Ne collisions. Without such numbers the assertion that 'many interesting studies' become accessible cannot be evaluated.
minor comments (1)
  1. [abstract] The abstract contains the phrasing 'on both: the proton and ion sides,' which is stylistically awkward and should be reworded for clarity.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the constructive comments, which correctly identify that the manuscript is conceptual in nature. We address each major comment below and will revise the text to clarify the scope and limitations of the presented ideas and studies.

read point-by-point responses

  1. Referee: [preliminary studies] The section following the analysis ideas (referred to as 'preliminary studies of what could be visible in the AFP') asserts that visibility studies have been performed yet contains no efficiency curves, acceptance calculations, resolution estimates, or background-rejection figures as a function of fragment charge, Z/A ratio, or rapidity. This absence is load-bearing for the central claim that AFP tagging is effective for the relevant nuclear fragments.

    Authors: We agree that the preliminary studies section contains only qualitative kinematic considerations based on AFP geometry and does not include quantitative metrics such as efficiency curves, acceptance calculations, or resolution estimates. No dedicated Monte Carlo simulations for nuclear fragments were performed. We will revise this section to explicitly describe the studies as initial conceptual assessments, remove any implication of detailed quantitative visibility studies, and note that full simulations are beyond the scope of this short note. revision: yes

  2. Referee: [introduction / abstract] No quantitative assessment is given of how the AFP acceptance, timing resolution, or tracking performance (originally tuned for forward protons in pp running) translates to the kinematics and charge states of nuclear fragments in p-O, O-O, or Ne-Ne collisions. Without such numbers the assertion that 'many interesting studies' become accessible cannot be evaluated.

    Authors: We agree that the manuscript provides no quantitative assessment of how AFP performance parameters translate to nuclear fragments. The text is intended as a short communication highlighting an experimental opportunity rather than a full feasibility study. We will revise the abstract and introduction to use more cautious language, stating that the configuration may enable access to studies pending future quantitative work on acceptance and resolution for the relevant charge states and kinematics. revision: yes

Circularity Check

0 steps flagged

No circularity; paper is a conceptual note with no derivations, fits, or self-referential predictions

full rationale

The manuscript presents analysis ideas for tagging charged fragments with AFP detectors in 2025 ion runs and mentions 'preliminary studies' without any equations, parameter fits, predictions of derived quantities, or load-bearing self-citations. No derivation chain exists that could reduce to its own inputs. The central claim is a feasibility statement resting on detector performance assumptions, but this is not circularity per the enumerated patterns; it is simply an unquantified assertion. This is the normal non-finding for a short conceptual note.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

No free parameters, axioms, or invented entities are introduced; the text is an ideas note based on existing detector hardware.

pith-pipeline@v0.9.1-grok · 5584 in / 840 out tokens · 13152 ms · 2026-06-28T07:58:56.363408+00:00 · methodology

discussion (0)

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Reference graph

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