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Study of collective phenomena via the production of heavy quarks and quarkonia in hadronic collisions

T0 review · 2 major / 4 minor · reviewed 2026-08-12 · deepseek-v4-flash

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Pith's one-line read ALICE reports that in Pb-Pb collisions the elliptic flow of non-prompt D0 mesons from beauty decays is lower than that of prompt D mesons by 3.2 standard deviations, indicating charm and beauty quarks thermalize differently in the…

desk verdict A solid ALICE proceedings summary whose one new physics claim—'no J/psi flow in pp'—is unsupported in the text; the rest is a competent recap of published results. read the letter →

arxiv 2411.15017 v1 pith:52HEU55L submitted 2024-11-22 hep-ex hep-phnucl-ex

Victor Valencia Torres (on behalf of ALICE collaboration) This is my paper · ORCID
classification hep-exhep-phnucl-ex
keywords ellipticflowheavyquarksquark-gluonplasmacharmoniumDmesonsbeautysmallcollisionsystemsALICE
verification ladder T0 review T1 audit T2 compute T3 formal

The pith

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

The reading

This contribution uses the azimuthal anisotropy of heavy-flavor particles to probe how strongly charm and beauty quarks couple to the quark-gluon plasma. In 30–50% central Pb–Pb collisions, the elliptic flow $v_2$ of non-prompt $D^0$ mesons from beauty decays sits below the flow of prompt charm mesons by 3.2 standard deviations for $2 < p_T < 8$ GeV/$c$, a difference the authors read as different degrees of thermalization. In high-multiplicity p–Pb collisions, inclusive muons from heavy-flavor decays show an elliptic flow peaking near $p_T = 2$ GeV/$c$, indicating that heavy quarks participate in collective motion in small systems. In high-multiplicity pp collisions, the $J/\psi$ $v_2$ is consistent with zero within 1 standard deviation, so no collective behavior is observed for charmonia there. Together these results tighten constraints on heavy-quark transport models and on whether QGP-like flow develops in small collision systems.

What carries the argument

The central observable is the elliptic flow coefficient $v_2$, the second Fourier harmonic of the azimuthal angle distribution of emitted particles, extracted with event-plane, two-particle correlation, scalar-product, and multiparticle-cumulant methods. The prompt/non-prompt separation uses the displaced decay vertex of $D^0$ mesons, so charm decays can be distinguished from beauty decays and the same coefficient can be compared across the two sectors. At forward rapidity, inclusive-muon and $J/\psi$ flow are obtained from dimuon/charged-hadron azimuthal correlations with non-flow contributions subtracted. The comparison with LIDO, AMPT, CGC, and TAMU calculations is what converts measured coefficients into statements about thermalization, energy loss, and charmonium regeneration.

What would settle it

Compute the same $v_2$ signals with four-particle cumulants in high-multiplicity p–Pb and pp collisions at $p_T > 2$ GeV/$c$; if the four-particle value is consistent with zero while the two-particle value is not, the two-particle flow is dominated by non-flow contamination and the collective-flow interpretation weakens.

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Extended reading notes

Core claim

On its own terms, the paper reports that ALICE measures the elliptic flow $v_2$ of prompt $D$, $D^+$, and $D^{*+}$ mesons and of non-prompt $D^0$ mesons in 30–50% central Pb–Pb collisions at 5.02 TeV. The non-prompt (beauty-decay) $v_2$ is lower than the prompt charm-meson $v_2$ by 3.2 standard deviations for $2 < p_T < 8$ GeV/$c$, and its weighted mean over $2 < p_T < 12$ GeV/$c$ is 2.7 standard deviations above zero; the LIDO transport model reproduces both the non-prompt $D^0$ and the beauty-decay-electron $v_2$. At forward rapidity in high-multiplicity p–Pb collisions at 8.16 TeV, inclusive muons from heavy-flavor decays show a $v_2$ that rises to about 0.07 near $p_T = 2$ GeV/$c$ and remains nonzero out to 10 GeV/$c$, with AMPT and CGC models describing the data. For $J/\psi$, the $v_2$ measured in high-multiplicity pp collisions is consistent with zero within 1 standard deviation over $1 < p_T < 12$ GeV/$c$, while in p–Pb it approaches the Pb–Pb values for $p_T > 4$ GeV/$c$, an observation the TAMU transport model reads as energy loss plus low-$p_T$ regeneration. The stated conclusion is that charm and beauty thermalize to different extents in the QGP, heavy quarks flow in p–Pb, and charmonia show no detectable collective flow in pp at current precision.

Load-bearing premise

The interpretation rests on assuming the measured azimuthal patterns are true collective motion, with leftover jet correlations, resonance decays, and detector effects fully removed by the correlation and event-plane methods.

Editorial extensions

If this is right

  • If the 3.2-standard-deviation gap is real, transport models must treat charm and beauty as separately thermalizing species, and the beauty-quark spatial diffusion coefficient can be extracted from non-prompt $D^0$ and $B$-meson $v_2$.
  • The 2.7-standard-deviation nonzero non-prompt $D^0$ $v_2$ implies that beauty quarks do join the collective flow, just less strongly than charm quarks.
  • A $J/\psi$ $v_2$ consistent with zero in high-multiplicity pp means there is no evidence for charmonium collectivity in pp at current precision.
  • The nonzero inclusive-muon $v_2$ for $p_T > 2$ GeV/$c$ in p–Pb, where heavy-flavor decays dominate, indicates heavy quarks flow in small systems and constrains initial-state versus final-state explanations.
  • The new four-particle cumulant extraction on Run 3 data should reduce non-flow contamination and settle whether the pp $J/\psi$ $v_2$ is genuinely zero or merely small.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

  • A natural extension would be to measure fully reconstructed $B$ mesons and compare their $v_2$ with non-prompt $D^0$ mesons, testing whether decay kinematics really are as negligible as the LIDO comparison assumes.
  • If the $J/\psi$ $v_2$ stays zero in pp while open-charm hadron $v_2$ in the same high-multiplicity pp events is nonzero, that would point to mass or color-charge effects in how small-system collectivity couples to heavy quarks; the present paper does not make that comparison.
  • A cross-check of the p–Pb inclusive-muon $v_2$ with four-particle cumulants would separate true collectivity from non-flow; if it vanishes, the heavy-quark-flow-in-small-systems conclusion would need revision.
  • The contrast between zero $J/\psi$ $v_2$ in pp and nonzero values in p–Pb suggests the collectivity in p–Pb may depend on the nuclear target rather than on multiplicity alone, a prediction that could be tested in high-multiplicity pp events at matched charged-particle multiplicity.
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Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, and a circularity audit.

Referee Report

2 major / 4 minor

Summary. This proceedings contribution by the ALICE collaboration summarizes recent elliptic-flow (v2) measurements for heavy-flavor particles in pp, p-Pb, and Pb-Pb collisions. It reports (i) a comparison of non-prompt D0-meson v2 with prompt non-strange D-meson v2 in Pb-Pb at 5.02 TeV, (ii) inclusive muon v2 in high-multiplicity p-Pb at 8.16 TeV, (iii) J/psi v2 in pp, p-Pb, and Pb-Pb systems, and (iv) preliminary Run 3 signal extraction for inclusive J/psi at mid and forward rapidity. The main new physics statement is that J/psi v2 in high-multiplicity pp collisions is consistent with zero within 1 sigma, which is interpreted as an absence of significant collective behavior for J/psi in small systems.

Significance. If the results hold, the reported 3.2-sigma difference between non-prompt D0 and prompt D meson v2 in Pb-Pb provides a direct constraint on charm and beauty thermalization in the quark-gluon plasma, and the near-zero J/psi v2 in high-multiplicity pp collisions is an important discriminator between initial-state and final-state explanations of small-system collectivity. The paper's strengths are that most measurements are drawn from published ALICE analyses with explicit references, the model comparisons are clearly labeled as external, and the Run 3 signal extraction is presented as preliminary. However, the pp J/psi v2 result, which carries the strongest new interpretive claim, is not documented in the text, preventing independent checking of the central conclusion.

major comments (2)
  1. [Results, Fig. 3 and following paragraph] The statement that J/psi v2 in high-multiplicity pp collisions is consistent with zero within 1 sigma, both as a function of pT and integrated over 1 <= pT <= 12 GeV/c, is the paper's only new physics conclusion not backed by a published ALICE analysis. The text gives no data points, no statistical or systematic uncertainties, and no description of the analysis method beyond one sentence on azimuthal correlations between inclusive dimuons and charged hadrons. The numerical content of Fig. 3 is not present in the manuscript text, and no public ALICE preliminary note is cited. Please provide a table of the v2 values with full uncertainties and a clear statement of the non-flow treatment, or cite a public preliminary result; without this, the claim cannot be checked.
  2. [Results, Fig. 2 and caption] The inclusive muon v2 measurement in p-Pb is described as having non-flow effects subtracted and as using two-particle correlations, but neither the subtraction procedure nor the systematic uncertainties are defined in the text. The interpretation that heavy quarks exhibit significant flow at mid-to-high pT depends on this subtraction. Since Ref. [9] is cited for the method, the figure caption and text should explicitly state that the result is a published ALICE measurement and point to the details in that reference, rather than describing it as a standalone new analysis.
minor comments (4)
  1. [References [1]-[12]] Several references have broken DOIs: Refs. [1], [2], [3], [5], [6], [7], [8], [9], [10], and [11] all resolve to arXiv:2307.14084, which is not the cited article. The reference list should be corrected before publication.
  2. [Introduction] There is a typo in the phrase 'compared with theorical models'; it should read 'theoretical models'.
  3. [Results, Fig. 1] The comparison with the LIDO model is presented qualitatively. For a proceedings this is acceptable, but a sentence on the uncertainty bands of the model predictions would help the reader assess the degree of agreement.
  4. [Summary] The summary states that Run 3 data 'will enable' more precise measurements immediately after presenting Run 3 signal extraction; consider rewording to clarify which quantities are preliminary and which are projections.

Circularity Check

0 steps flagged · score 0.0 of 10

No circularity: the paper reports ALICE measurements and compares them with independent model calculations; no fitted parameter is renamed as a prediction and no load-bearing self-citation supplies the physics result.

full rationale

This is a proceedings contribution that presents measured v2 coefficients for open heavy flavor and quarkonia in pp, p–Pb, and Pb–Pb collisions, with comparisons to external theoretical models (LIDO, AMPT, CGC, TAMU). The central statements—non-prompt D0 v2 lower than prompt D mesons with 3.2σ significance, inclusive muon v2 in p–Pb showing a peak around 0.07, and J/ψ v2 in high-multiplicity pp consistent with zero within 1σ—are experimental results backed by cited ALICE analyses, not quantities derived from the models within this paper. No model parameter is fitted to the data shown here, no equation is introduced that would make a prediction equal to an input by construction, and the interpretation of the measurements as evidence for or against thermalization is an externally checkable physics claim, not a tautology. The heavy reliance on ALICE self-citations is standard for a collaboration summary and is not load-bearing in a circular way: the cited measurements are independent published results, and the models cited are not authored by the presenter. The absence of detailed data points for the pp J/ψ v2 in the text is a presentation/verifiability limitation, not a circularity. Therefore the derivation chain is self-contained with respect to the input data and the appropriate circularity score is 0.

Assumptions & free parameters 0 free parameters · 3 assumptions · 0 invented entities

The paper introduces no free parameters or invented entities; it relies on standard heavy-ion analysis methods and on external transport and initial-state models that are not fitted within the paper. The main assumptions are the validity of the v2 extraction methods and the interpretative models.

assumptions (3)
  • domain assumption Heavy-quark production occurs in initial hard scattering and can be described by perturbative QCD.
    Invoked in the Introduction as the basis for using heavy quarks as QGP probes.
  • domain assumption The v2 extraction methods (two-particle correlations, scalar product, cumulants) correctly separate collective flow from non-flow backgrounds.
    The interpretation of the measured coefficients as elliptic flow relies on non-flow subtraction and event-plane determination, as used in Figures 2 and 3.
  • domain assumption The external models used for comparison (LIDO, AMPT, CGC, TAMU) are valid descriptions of heavy-quark transport and initial-state correlations.
    The paper compares data to these models and interprets agreement as physical insight, assuming the models capture the relevant physics.

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Cite this review

Pith. "Pith review of Study of collective phenomena via the production of heavy quarks and quarkonia in hadronic collisions." pith.science (2026). https://pith.science/paper/52HEU55L

@misc{pith2026241115017,
  author       = {Pith},
  title        = {Pith review of: Study of collective phenomena via the production of heavy quarks and quarkonia in hadronic collisions},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/52HEU55L}},
  note         = {Machine review of arXiv:2411.15017}
}
abstract

Open heavy flavor and quarkonia have long been identified as ideal probes for understanding the quark-gluon plasma (QGP). Heavy quarks are produced in the early stage of the heavy-ion collisions. Therefore they experience the evolution of the medium produced, providing an important tool to investigate the properties of the QGP. In particular, the magnitude of the elliptic flow measured at the LHC is interpreted as a signature of the charm-quark thermalization in the QGP. This is reflected in the azimuthal anisotropies of the final particles. In addition, the observation of collective-like effects in high-multiplicity pp and p--Pb collisions provides new insights on the evolution of QGP-related observables going from large to small collision systems. A better understanding of heavy-quark energy loss, quarkonium dissociation, and production mechanism can therefore be obtained with those system-size dependent observables. We present recent results of the $\mathrm{J}/\psi $ and open heavy-flavor hadrons flow in pp, p--Pb, and Pb--Pb collisions carried out by the ALICE collaboration.

Figures

Figures reproduced from arXiv: 2411.15017 by the authors.

Figure 1
Figure 1. Left: 𝑣2 of non-prompt 𝐷 0 mesons (blue) and prompt non-strange 𝐷 mesons (red) as a function of 𝑝T [3]. Right: 𝑣2 of non-prompt 𝐷 0 mesons [3] (blue) and electrons from beauty-hadron decays [4] (red) as a function of 𝑝T. Both measurements are measured in the 30–50% centrality class in Pb–Pb collisions and are compared with LIDO model predictions [5], [6]. These measurements will provide important constraints to mode… view at source ↗
Figure 2
Figure 2. Flow of inclusive muon 𝑣 𝜇 2 as a function of 𝑝T at forward rapidity in high-multiplicity p–Pb collisions at √ 𝑠NN = 8.16 TeV. This new measurement covers for the first time a wide transverse momentum range of 0.5 < 𝑝T < 10 GeV/𝑐 in the forward rapidity region. The data reveal an initial increase in 𝑣 𝜇 2 with rising 3 [PITH_FULL_IMAGE:figures/full_fig_p003_2.png] view at source ↗
Figure 3
Figure 3. The 𝑝T dependence of 𝑣 J/𝜓 2 in pp, p–Pb [10], and Pb–Pb [11] collision systems. In [PITH_FULL_IMAGE:figures/full_fig_p004_3.png] view at source ↗
Figures from the paper (1 more)
Figure 4
Figure 4. Figure 4: Left: Fit of the invariant mass distribution 𝑚𝑒𝑒 at midrapidity in pp collisions at √ 𝑠 = 13.6 TeV, showing the extracted inclusive J/𝜓 and 𝜓(2S) signals. Right: Fits of 𝑚𝜇𝜇, 𝑣 𝜇𝜇 2 {2} and 𝑣 𝜇𝜇 2 {4} distributions at forward-rapidity in Pb–Pb collisions at √ 𝑠NN = 5.3…

Discussion (0). Continue with ORCID to comment.

Reference graph

Works this paper leans on

10 extracted references · 2 canonical work pages

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Reviewed August 12, 2026 · model on record in the stance chip above.