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Jet and jet substructure: ALICE results

T0 review · 0 major / 6 minor · reviewed 2026-08-08 · deepseek-v4-flash

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Pith's one-line read ALICE jet data locate the parton-to-hadron transition inside jets.

desk verdict A faithful conference summary of four published ALICE jet measurements; no new physics, no misquotes, and no reason to treat it as a primary source. read the letter →

arxiv 2502.06396 v2 pith:PQIOTQGZ submitted 2025-02-10 nucl-ex hep-ex

Haidar Mas'ud Alfanda This is my paper · ORCID
classification nucl-exhep-ex
keywords jetsubstructureenergy-energycorrelatorsparton-hadrontransitionquenchingquark-gluonplasmanuclearmodificationfactorALICEheavy-ioncollisions
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 conference proceeding reports ALICE's recent jet measurements in pp, p–Pb, and Pb–Pb collisions. The headline result is that in pp collisions at 5.02 TeV, the energy-energy correlator inside charged-particle jets has a peak whose position, at $\langle p_{\mathrm{T,ch}}^{\mathrm{jet}}\rangle R_L = 2.39 \pm 0.17$ GeV/c, is independent of jet $p_{\mathrm{T}}$. ALICE interprets this turnover as the transition from perturbative parton splittings to non-perturbative hadronization. In p–Pb collisions the inclusive jet nuclear modification factor is consistent with unity, and in Pb–Pb collisions the semi-inclusive recoil-jet yield is suppressed at intermediate $p_{\mathrm{T}}$, showing medium-induced energy loss. A sympathetic reader would take the paper as evidence that jet substructure observables can directly expose the hadronization scale within jets.

What carries the argument

The central object is the jet energy-energy correlator (EEC), defined as the $p_{\mathrm{T}}$-weighted distribution of angular separations $R_L$ between pairs of particles inside a jet, normalized by the jet $p_{\mathrm{T}}$ squared. Its two scaling regimes—perturbative at large $R_L$, linear 'free hadron' at small $R_L$—and the turnover peak between them carry the argument. The turnover position, quoted as $\langle p_{\mathrm{T,ch}}^{\mathrm{jet}}\rangle R_L = 2.39 \pm 0.17$ GeV/c, is the paper's principal quantitative claim. Secondary machinery includes the nuclear modification factor $R_{p\mathrm{Pb}}$ for inclusive jets and the hadron-triggered semi-inclusive recoil-jet observable $\Delta_{\mathrm{recoil}}$ with its ratio $I_{AA}$.

What would settle it

Measuring the EEC turnover in the same pp dataset with a scan of jet radii and $p_{\mathrm{T}}$ cuts, then checking whether the fitted peak stays at $\langle p_{\mathrm{T,ch}}^{\mathrm{jet}}\rangle R_L = 2.39 \pm 0.17$ GeV/c, would settle the claim; a drift with jet radius, collision energy, or jet $p_{\mathrm{T}}$ beyond uncertainties would refute the universal hadronization-scale interpretation.

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Extended reading notes

Core claim

On its own terms, the paper's central finding is that the jet energy-energy correlator in pp collisions at $\sqrt{s}=5.02$ TeV exhibits a universal turnover at $\langle p_{\mathrm{T,ch}}^{\mathrm{jet}}\rangle R_L = 2.39 \pm 0.17$ GeV/c across all measured charged-jet $p_{\mathrm{T}}$ intervals. At large angular separations the correlator follows perturbative QCD scaling; at small separations it falls into a linear 'free hadron' scaling region; the peak between them marks the scale at which partons become confined into hadrons. The paper reports this as a direct observation of the parton-hadron transition inside jets, supported by comparison to a next-leading-logarithmic pQCD calculation. It also reports that the p–Pb inclusive jet yield is unmodified within uncertainties, and that Pb–Pb semi-inclusive recoil jets show a $p_{\mathrm{T}}$-dependent suppression ($I_{AA}$ above unity below 10 GeV/c, below unity from 10 to 80 GeV/c) consistent with energy loss and surface bias.

Load-bearing premise

The paper's reading of the 2.39 GeV/c peak as the hadronization scale assumes that the theoretical curve used for the large-angle region is correct and that detector effects do not move the peak; if either assumption fails, the number loses its stated physical meaning.

Editorial extensions

If this is right

  • If the EEC turnover is a universal hadronization scale, similar measurements at other collision energies should reproduce the same $\langle p_{\mathrm{T,ch}}^{\mathrm{jet}}\rangle R_L$ peak position.
  • The agreement of the perturbative region with the NLL pQCD calculation means EEC can serve as a clean test of perturbative QCD, with deviations cleanly locating non-perturbative effects.
  • The p–Pb result $R_{p\mathrm{Pb}} \approx 1$ constrains cold nuclear matter effects, so any future modification in Pb–Pb can be attributed to hot QCD matter.
  • The Pb–Pb $I_{AA}$ pattern—enhancement at low $p_{\mathrm{T}}$ and suppression at intermediate $p_{\mathrm{T}}$—discriminates among jet-energy-loss models, with JETSCAPE capturing the data best.
  • With Run 3 data, the EEC turnover can be measured with higher precision and at higher jet $p_{\mathrm{T}}$, sharpening the determination of the hadronization scale.
  • The EEC turnover in Pb–Pb jets could be measured to test whether the quark–gluon plasma shifts the parton-hadron transition scale.

Reading between the lines

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

  • If the turnover is indeed universal, the EEC could become a practical hadronization-scale thermometer: the same measurement in other collision systems or at other energies would reveal whether the confinement scale changes with the medium.
  • The quoted $2.39 \pm 0.17$ GeV/c sits in the non-perturbative regime, so it would be natural to test whether string-fragmentation or cluster-hadronization Monte Carlo models reproduce the peak position, not just the overall EEC shape.
  • The 'free hadron' linear-scaling region at small $R_L$ is described as purely combinatorial; this could be checked directly with a toy Monte Carlo of uncorrelated hadrons, which would either confirm or challenge that interpretation.
  • For the p–Pb result, the statement that jet quenching is below current sensitivity implies that more precise p–Pb data could reveal small nuclear PDF effects that are currently hidden by uncertainties.
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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

0 major / 6 minor

Summary. This proceedings contribution summarizes recent ALICE measurements of jets and jet substructure in pp, p–Pb, and Pb–Pb collisions at √s_NN = 5.02 TeV. The paper is organized around three measurements: the energy–energy correlator (EEC) in pp collisions, the inclusive charged-particle jet nuclear modification factor R_pPb in p–Pb collisions, and the semi-inclusive hadron-triggered recoil jet yield modification I_AA in Pb–Pb collisions. For each observable, the paper gives the definition (or a brief description), shows the experimental result, and compares it with model predictions. A headline quantitative result is the position of the EEC peak at ⟨p_T^ch,jet⟩ R_L = 2.39 ± 0.17 GeV/c, interpreted as the scale of the parton–hadron transition.

Significance. The paper does not present new experimental data; its value lies in providing a concise and accessible overview of three important ALICE results, one of which (the EEC turnover) is a recent and physically significant measurement. The summary is faithful to the cited publications, and the comparisons with POWHEG+PYTHIA8, JETSCAPE, JEWEL, and the Hybrid model give the reader a useful map of the current theoretical landscape. Because the underlying results are peer-reviewed and the proceedings does not introduce new claims, the main risk is misquotation or loss of caveats; I find no such problem. The paper is therefore reliable as a conference-proceedings summary, though it remains a secondary source.

minor comments (6)
  1. [Section 2 and throughout] The unit "Ge V/c" (and "Te V") appears in several places due to a typographical spacing issue; these should read "GeV/c" and "TeV", respectively.
  2. [Section 4] The phrase "above untiy" should read "above unity".
  3. [Section 2] The sentence "The data deviates from the perturbative scaling" should use the plural verb: "The data deviate".
  4. [Section 2] Consider rewording "the turnover of the EEC peaks" to "the turnover of the EEC peak", since each pT interval shows a single peak; alternatively, "the peak turnover" would be clearer.
  5. [Section 2] The statement that the turnover occurs at 2.39 ± 0.17 GeV/c "across all pT intervals" would benefit from a qualifier such as "within the current precision" and a pointer to Ref. [2] for the detailed analysis, to avoid implying that this proceedings presents an independent derivation.
  6. [Section 4] The sentence "Since the trigger-normalized jet yield is independent of pT,trig, the uncorrelated background will be subtracted from Δrecoil" is unclear; please rephrase to reflect the actual procedure, e.g., that the subtraction removes the combinatorial background from uncorrelated trigger-jet pairs.

Circularity Check

0 steps flagged · score 0.0 of 10

No circularity: the paper is a proceedings summary of published ALICE measurements compared with external models; no fitted parameter is renamed as a prediction and no load-bearing argument reduces to its own input.

full rationale

The paper reports existing ALICE measurements and compares them with external model calculations. Section 2's headline value, <pTch,jet> R_L = 2.39 ± 0.17 GeV/c, is explicitly attributed to the published ALICE analysis in Ref. [2], not derived in this proceedings. Equation (1) is a definition of the energy-energy correlator, not a derived result. Section 3 compares R_pPb with POWHEG+PYTHIA8 and nPDF sets; Section 4 compares I_AA with JETSCAPE, JEWEL, and the Hybrid model. These are external benchmarks, not outputs of the paper itself. Self-citations to ALICE papers are appropriate references to peer-reviewed, published measurements and do not constitute load-bearing circularity because the underlying results are externally reproducible and the proceedings introduces no new fitting or parameter extraction. The interpretive claim that the EEC peak marks the parton-hadron transition is a physical interpretation of an independently measured observable, not a circular reduction. No claimed prediction is equivalent by construction to its input, and no uniqueness theorem or ansatz is imported from the authors' prior work. Therefore the circularity score is 0.

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

The paper introduces no free parameters or new entities. Its claims rest entirely on the correctness of the cited experimental and theoretical works.

assumptions (3)
  • domain assumption Published ALICE measurements cited in refs [2], [4], [7], and [8] are correct.
    The entire paper is a summary of these results; if any were wrong, the paper's conclusions would fail.
  • domain assumption The next-leading-logarithmic pQCD calculation of Ref. [3] accurately describes the perturbative region of the EEC.
    Used in Section 2 to interpret the data deviation at small R_L as non-perturbative.
  • domain assumption The models (POWHEG+PYTHIA8, JETSCAPE, JEWEL, Hybrid) provide valid comparisons for the data.
    The paper draws conclusions about model-data agreement in Sections 3 and 4 based on these models.

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Cite this review

Pith. "Pith review of Jet and jet substructure: ALICE results." pith.science (2026). https://pith.science/paper/PQIOTQGZ

@misc{pith2026250206396,
  author       = {Pith},
  title        = {Pith review of: Jet and jet substructure: ALICE results},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/PQIOTQGZ}},
  note         = {Machine review of arXiv:2502.06396}
}
read the original abstract

Jets and their substructure in pp collisions offer a unique opportunity to probe various aspects of quantum chromodynamics (QCD), ranging from perturbative QCD (pQCD) tests to studies of non-perturbative phenomena such as hadronization. They also probe the transition between perturbative and non-perturbative regimes. In heavy-ion collisions, jets serve as a novel tool to investigate the microscopic properties of the deconfined quark-gluon plasma (QGP). Recently, significant progress has been made in developing jet substructure observables to explore these properties. The ALICE experiment is particularly well-suited for jet measurements due to its high-precision tracking system, which is especially beneficial for detecting low transverse momentum jets. This contribution will highlight recent ALICE measurements of inclusive and semi-inclusive jets, along with various jet substructure observables in pp, p-Pb, and Pb-Pb collisions. The comparisons between data and predictions from Monte Carlo (MC) models as well as analytical calculations will be discussed.

Figures

Figures reproduced from arXiv: 2502.06396 by the authors.

Figure 1
Figure 1. Normalized ΣEEC distributions as a function of ⟨p ch jet T ⟩RL [2]. 3. Inclusive jets in p–Pb collisions The nuclear modification factor, R ch jet pPb of charged-particle jet yield in minimum bias p–Pb collisions is quantified by comparing the jet cross sec￾tion in p–Pb collisions normalized by the number of nucleons of the Pb ion, A = 208, to the jet cross section in pp collisions [PITH_FULL_IMAGE:figures/full_fig… view at source ↗
Figure 2
Figure 2. Inclusive charged-particle jet nuclear modification factor, [PITH_FULL_IMAGE:figures/full_fig_p004_2.png] view at source ↗
Figure 3
Figure 3. The IAA(p ch jet T ) for recoil jets triggered by hadrons as a function of p ch jet T in Pb–Pb collisions at √ sNN = 5.02 TeV compared to MC model simulations [7]. 5. Conclusion We have presented new ALICE measurements of jets in pp, p–Pb, and Pb–Pb collisions. These measurements provide valuable insights into the behavior of jets and their substructure. The observables discussed not only highlight the current under… view at source ↗

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Reference graph

Works this paper leans on

12 extracted references · 12 linked inside Pith

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Reviewed August 8, 2026 · model on record in the stance chip above.