arxiv: 2604.07184 · v1 · submitted 2026-04-08 · ⚛️ nucl-ex · hep-ex· nucl-th

Recognition: no theorem link

Recent ALICE results from light-ion collision systems

Abhi Modak (on behalf of the ALICE Collaboration)

Authors on Pith no claims yet

Pith reviewed 2026-05-10 17:45 UTC · model grok-4.3

classification ⚛️ nucl-ex hep-exnucl-th

keywords ALICELHClight ion collisionspseudorapidity densityelliptic flowtriangular flowneutral pion suppressionsmall systems

0 comments

The pith

ALICE finds neutral pion suppression in oxygen-oxygen 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 new measurements by the ALICE Collaboration in proton-oxygen, oxygen-oxygen, and neon-neon collisions at the LHC. These include the primary charged-particle pseudorapidity density and the elliptic and triangular flow coefficients for charged particles. It also presents evidence for the suppression of neutral pion yields in OO collisions relative to a proton-proton baseline. Comparisons with theoretical models are used to interpret particle production, collective phenomena, and parton energy loss in these small systems.

Core claim

The central claim is that the new data from light-ion collisions demonstrate measurable elliptic and triangular flow along with a clear suppression of neutral pion production in oxygen-oxygen collisions compared to proton-proton, supplying essential constraints for models describing dynamics in small collision systems.

What carries the argument

The light-ion collision systems (pO, OO, Ne-Ne) at LHC energies, with the reported observables serving to probe the transition from small to large system behavior through flow coefficients and yield suppression.

Load-bearing premise

The assumption that the proton-proton baseline and the chosen theoretical models provide a reliable reference without significant unaccounted systematic uncertainties in the light-ion regime.

What would settle it

If neutral pion production in OO collisions shows no suppression relative to the proton-proton baseline when properly normalized, the reported experimental evidence of suppression would not hold.

Figures

Figures reproduced from arXiv: 2604.07184 by Abhi Modak (on behalf of the ALICE Collaboration).

**Figure 1.** Figure 1: Dependence of ⟨dNch/dη⟩ on the collision centrality in OO collisions at √ sNN = 5.36 TeV. Grey bands show the systematic uncertainties. Statistical uncertainties are within the marker size. Predictions from various theoretical models are superimposed. The resulting charged-particle pseudorapidity density, averaged over |η| < 0.5 and denoted by ⟨dNch/dη⟩, is presented in [PITH_FULL_IMAGE:figures/full_fi… view at source ↗

**Figure 2.** Figure 2: (Left) Values of (2/⟨Npart⟩)⟨dNch/dη⟩ for the 5% central OO and Ne–Ne collisions compared to previous measurements in pp(p¯p), pA(dA), and central heavyion collisions as a function of √ sNN. (Right) Dependence of (2/⟨Npart⟩)⟨dNch/dη⟩ on the ⟨Npart⟩ for OO and Ne–Ne collisions at √ sNN = 5.36 TeV. ALICE data from Pb–Pb collisions at the LHC energies are shown for comparison. In [PITH_FULL_IMAGE:figures/f… view at source ↗

**Figure 3.** Figure 3: Centrality dependence of v2{2}, v3{2}, and v2{4} for charged particles with 0.2 < pT < 3 GeV/c and |η| < 0.8 in OO (left) and Ne–Ne (right) collisions at √ sNN = 5.36 TeV. The measurements are compared with Trajectum calculations with NLEFT and PGCM inputs. 5. Observation of parton energy loss This section presents the measurements of invariant yields of neutral pions at midrapidity (|y| < 0.8) in the pT… view at source ↗

**Figure 4.** Figure 4: Measured ROO of π 0 in comparison to various theoretical predictions. Models in the left plot are baselines that do not include parton energy loss, while models on the right include energy loss. Model references are included in the figure [PITH_FULL_IMAGE:figures/full_fig_p007_4.png] view at source ↗

read the original abstract

This article presents recent measurements by the ALICE Collaboration in proton--oxygen (pO), oxygen--oxygen (OO), and neon--neon (Ne--Ne) collisions delivered by the LHC in July 2025. Measurements of the primary charged-particle pseudorapidity density and the elliptic and triangular flow coefficients of charged particles are reported. Experimental evidence of the suppression of neutral pion yields in OO collisions relative to the proton--proton baseline is also discussed. Comparisons of these new data with theoretical models provide key input to understand particle production, collective phenomena, and parton energy loss in small collision systems.

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.

Desk Editor's Note private letter to a colleague

This is straightforward new ALICE data from the 2025 pO, OO, and NeNe runs on densities, flow, and pion suppression, useful for small-system studies but not a major shift.

read the letter

The main takeaway is that ALICE has put out the first results from their light-ion collisions at the LHC last summer. They measure charged-particle pseudorapidity density, v2 and v3 flow coefficients across pO, OO, and NeNe, plus neutral pion yield suppression in OO versus a pp baseline. Model comparisons are included mainly for context on particle production and collective effects in these smaller systems. This extends their earlier pp and PbPb work by filling in intermediate system sizes, which matters for questions about when flow and energy loss appear. The data come from established ALICE methods, so the core measurements look reliable with no obvious circularity or invented quantities. What the paper does well is deliver these direct observables promptly after the run, giving the community fresh points to test ideas on the onset of collective behavior without relying on heavy parameter tuning. Soft spots are limited. The abstract leaves out full details on event selection, uncertainty breakdowns, and exact model versions, which a full read would need to confirm are handled properly. The pion suppression is described as evidence but lacks visible significance numbers here, so that part might need tighter scrutiny in the text. Overall the central claims hold up as standard experimental reporting rather than overreaching. This is for heavy-ion physicists working on small systems or QGP signatures, especially those who model flow and suppression across system sizes. A reader looking for new constraints on theory would find it worthwhile. It deserves peer review because new LHC collision species data is worth checking in detail even when incremental, and the experimental grounding is solid enough to justify referee time.

Referee Report

0 major / 2 minor

Summary. The manuscript reports recent ALICE measurements in pO, OO, and NeNe collisions at the LHC, including the primary charged-particle pseudorapidity density, elliptic (v2) and triangular (v3) flow coefficients of charged particles, and suppression of neutral pion yields in OO relative to a pp baseline. These data are compared to theoretical models to provide input on particle production, collective phenomena, and parton energy loss in small systems.

Significance. If the measurements hold, they supply important new constraints on the onset of collectivity and medium-induced effects in light-ion systems, helping to bridge pp and heavy-ion regimes. The direct experimental nature of the results, with model comparisons offered only as context, strengthens their utility for the field.

minor comments (2)

[Abstract] The abstract does not specify the collision energies or center-of-mass energies per nucleon pair, which are essential for placing the new light-ion results in context with existing pp and PbPb data.
[Model comparisons] Section on model comparisons would benefit from explicit statements on which observables are most sensitive to specific model ingredients (e.g., initial-state geometry vs. final-state interactions) to guide readers on the interpretive weight of each comparison.

Simulated Author's Rebuttal

0 responses · 0 unresolved

We thank the referee for reviewing our manuscript and recommending minor revisions. The referee's summary accurately captures the content and significance of our ALICE measurements in pO, OO, and NeNe collisions. No specific major comments were raised in the report.

Circularity Check

0 steps flagged

No circularity: direct experimental measurements with no derivations or self-referential claims

full rationale

This is an experimental results paper reporting new ALICE data on charged-particle pseudorapidity density, elliptic/triangular flow (v2, v3), and neutral-pion suppression in pO, OO, and NeNe collisions. No derivation chain, first-principles predictions, or fitted parameters renamed as outputs exist. Model comparisons serve only as interpretive context and do not reduce any claimed result to the input data by construction. No self-citations are load-bearing for uniqueness theorems, ansatze, or redefinitions. The paper is self-contained against external benchmarks as a data presentation.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

This is an experimental measurement paper; the claims rest on standard LHC data-taking and analysis techniques already established in the field. No new free parameters, axioms, or invented entities are introduced.

pith-pipeline@v0.9.0 · 5395 in / 990 out tokens · 48780 ms · 2026-05-10T17:45:28.196357+00:00 · methodology

discussion (0)

Reference graph

Works this paper leans on

10 extracted references · 1 canonical work pages

[1]

Bierlich, G

C. Bierlich, G. Gustafson, L. L¨ onnblad, and H. ShahJHEP10(2018) 134

2018
[2]

Linet al

Z.-W. Linet al. Phys. Rev. C72(2005) 064901

2005
[3]

Schenke, P

B. Schenke, P. Tribedy, and R. VenugopalanPhys. Rev. Lett.108(2012) 252301

2012
[4]

Garcia-Montero, H

O. Garcia-Montero, H. Elfner, and S. SchlichtingPhys. Rev. C109(2024) 044916. [15]ALICECollaboration, I. J. Abualrobet al.arXiv:2509.06428 [nucl-ex]

work page arXiv 2024
[5]

Bilandzicet al

A. Bilandzicet al. Phys. Rev. C89(2014) 064904

2014
[6]

Y. Zhou, X. Zhu, P. Li, and H. SongPhys. Rev. C91(2015) 064908

2015
[7]

LoizidesPhys

C. LoizidesPhys. Rev. C113(2026) 014914. [19]ALICECollaboration, S. Acharyaet al. Phys. Rev. Lett.123(2019) 142301

2026
[8]

Nijs and W

G. Nijs and W. van der ScheePhys. Rev. C106(2022) 044903

2022
[9]

D. LeeAnn. Rev. Nucl. Part. Sci.75(2025) 109–128. 9

2025
[10]

Frosiniet al

M. Frosiniet al. Eur. Phys. J. A58(2022) 62

2022