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REVIEW 3 major objections 5 minor 19 references

Production of Jets at STAR

T0 review · 3 major / 5 minor · reviewed 2026-08-06 · deepseek-v4-flash

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Pith's one-line read STAR jet measurements at 200 GeV show strong jet quenching in Au+Au collisions and trace the p+Au suppression to an event-activity selection bias rather than to in-medium energy loss.

desk verdict A clean, honest proceedings summary of existing STAR jet results; the only soft spot is the under-supported p+Au event-activity claim, which is better assessed in the cited PRC paper. read the letter →

arxiv 2507.23471 v1 pith:ZR6JLCTO submitted 2025-07-31 hep-ex nucl-ex

Michal Svoboda This is my paper · ORCID
classification hep-exnucl-ex PACS 25.75.-q13.87.-a
keywords jetquenchingquark-gluonplasmaheavy-ioncollisionsp+AuAu+Aueventactivitysemi-inclusivejetsRHIC
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 paper argues that jet suppression measured at RHIC at $\sqrt{s_{\mathrm{NN}}}=200$ GeV has two distinct causes depending on collision system. In Au+Au, central collisions suppress charged-particle jet yields to $R_{\mathrm{CP}} \sim 0.5$ relative to peripheral collisions, roughly independent of jet $p_{\mathrm{T}}$, and the data are consistent with theoretical models of parton energy loss in the quark-gluon plasma. In p+Au, high-event-activity events also suppress jet yields, but the suppression is equal on trigger and recoil sides and leaves dijet momentum balance and azimuthal separation unchanged, which is not the signature of in-medium energy loss. The paper attributes the p+Au suppression to a negative correlation between the forward event-activity measure and the underlying hard-scattering scale $Q^2$, so that high-EA event classes preferentially select softer hard scatters.

What carries the argument

The argument is carried by semi-inclusive, trigger-normalized jet yields and by forward event-activity selection. Jets are reconstructed with the anti-$k_{\mathrm{T}}$ algorithm for radii $R=0.2$--$0.5$ from charged tracks in the TPC, with full jets adding BEMC energy; underlying-event contributions are subtracted using mixed-event techniques. The semi-inclusive observable $I_{\mathrm{AA}}$ compares trigger-normalized recoil-jet yields in AA to pp for identical $\gamma$ or $\pi^0$ triggers, cancelling trigger and underlying-event biases so that remaining suppression is attributable to the medium. Inclusive jet results use $R_{\mathrm{CP}}$ (central vs peripheral yields scaled by binary-collision counts) and $R_{\mathrm{AA}}$ (AA vs pp yields). For p+Au, the key mechanism is the BBC in the Au-going direction ($\eta \in [-5,-3.4]$): its summed ADC defines high- and low-event-activity classes, and the large pseudorapidity gap between the event-activity measurement and midrapidity jets is what allows the paper to separate event-activity selection from in-medium effects.

What would settle it

Redo the p+Au high-/low-EA jet-yield comparison using an event-activity estimator that does not saturate and is separated from the hard process (for example, spectator energy or a segmented forward detector): if the equal trigger-side and recoil-side suppression and the unchanged dijet $p_{\mathrm{T}}$ imbalance survive the redefinition, the anti-correlation interpretation is supported; if the suppression becomes recoil-side dominated or disappears, the paper's p+Au conclusion fails.

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Extended reading notes

Core claim

On its own terms, the paper establishes that jets are strongly modified in central Au+Au at $\sqrt{s_{\mathrm{NN}}}=200$ GeV and not modified in the way energy loss would produce in high-EA p+Au. The Au+Au evidence is threefold: inclusive jet $R_{\mathrm{CP}} \sim 0.5$ with weak $p_{\mathrm{T}}$ dependence; $R_{\mathrm{AA}}$ for charged jets described by several transport and effective-theory calculations; and semi-inclusive $\gamma$- and $\pi^0$-triggered recoil jet yields suppressed at $R=0.2$ and less so at $R=0.5$, indicating energy redistribution to larger angles. The p+Au evidence is that high-EA events suppress trigger-side and recoil-side jets equally and show no significant change in the ratio of $p_{\mathrm{T}}$ imbalance or azimuthal dijet separation between high- and low-EA events. Because such symmetric suppression is not a quenching signature, the paper concludes the small-system suppression reflects an event-activity/hard-scale anti-correlation rather than jet-medium interaction.

Load-bearing premise

The load-bearing assumption is that the summed BBC signal in the Au-going direction, despite detector saturation, is a valid event-activity proxy whose correlation with the hard-scattering scale is not itself an artifact of autocorrelations with the jets measured at midrapidity.

Editorial extensions

If this is right

  • Central Au+Au collisions at $\sqrt{s_{\mathrm{NN}}}=200$ GeV suppress inclusive charged-jet yields by roughly a factor of two, a signature of strong jet interaction with the quark-gluon plasma at RHIC energies.
  • The weakening of semi-inclusive recoil-jet suppression from $R=0.2$ to $R=0.5$ shows that a larger jet cone recovers more of the lost energy, constraining the angular scale of medium-induced energy redistribution.
  • The $\gamma$- and $\pi^0$-triggered recoil yields are consistent within uncertainties, implying a larger average energy loss for $\pi^0$-triggered recoil jets given their steeper trigger spectrum, which constrains the flavor and path-length dependence of quenching.
  • In p+Au, high-EA and low-EA events show no significant difference in dijet $p_{\mathrm{T}}$ imbalance or azimuthal separation, ruling out a strong in-medium energy-loss component in the observed high-EA jet suppression.
  • The measured inclusive jet spectra extend to about 50 to 60 GeV/c, providing an RHIC baseline for comparing jet suppression patterns with LHC data after accounting for spectral-shape and quark/gluon-fraction differences.

Reading between the lines

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

  • The p+Au result implies that event-activity-based "centrality" in small systems may systematically select lower-$Q^2$ hard scatters; other small-system observables that use the same event-activity classes may carry the same bias.
  • A direct testable consequence is that the high-/low-EA jet-yield ratio in p+Au should be reproducible by Monte Carlo simulations without any medium, provided the simulation implements the same BBC event-activity selection.
  • The same forward-activity method could be applied to asymmetric small systems such as O+Au or d+Au to see whether the anti-correlation scales with the size of the heavy ion, and to future high-luminosity RHIC data for full-jet reconstruction.
  • If the event-activity/hard-scale anti-correlation is the cause, the suppression in p+Au should be independent of jet radius, unlike the Au+Au case where the $R$ dependence of $I_{\mathrm{AA}}$ is a quenching signature.
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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

3 major / 5 minor

Summary. The manuscript is a short proceedings-style report on behalf of the STAR Collaboration, summarizing recent STAR jet measurements at sqrt(s_NN) = 200 GeV. It covers three topics: inclusive charged-particle jet R_CP and R_AA in Au+Au collisions; semi-inclusive direct-photon+jet and pi0+jet I_AA in central Au+Au collisions; and event-activity-dependent semi-inclusive jet spectra in p+Au collisions using a BBC-based event-activity classifier. The central claims are that Au+Au jet yields are significantly suppressed, consistent with strong jet interactions with the quark-gluon plasma, and that high-event-activity p+Au suppression is not due to in-medium energy loss but to an anti-correlation between event activity and the underlying hard scale Q^2. All quantitative results and figures are taken from Refs. [5], [17], and [19].

Significance. If the results hold, the Au+Au R_CP/R_AA and I_AA measurements provide important RHIC-era constraints on jet quenching, and the p+Au event-activity study bears directly on the question of whether small-system suppression is a final-state or selection effect. The manuscript is a useful, concise entry point to these STAR results and clearly credits the underlying references. Its main limitation, however, is that it contains no original numerical data or analysis: every figure is labelled as taken from a prior STAR publication, so the scientific value resides in the referenced papers rather than in this manuscript itself.

major comments (3)
  1. [§3.3, Fig. 5, and Conclusions] The conclusion that high-event-activity suppression in p+Au reflects a negative correlation between event activity and Q^2 rather than in-medium energy loss is not supported by the material presented in this manuscript. The only validation of the BBC ADC event-activity classifier is the sentence: 'Despite detector signal saturation effects, correlations between EA measured by the BBC and midrapidity charged particle density confirm the suitability of this method.' No saturation correction, correlation strength, or demonstration that the 30% low/high event-activity classes are not in a saturated plateau is given. Because the pT-imbalance and dijet azimuthal-separation ratios show no significant differences, they are null results and cannot independently validate the event classes. The authors should include the event-activity validation from Ref. [19] or explicitly cite the specific figure/table there before the Q^2 anti-correlation interpretation can be assessed.
  2. [§3.2, Fig. 4, and text near 'within the same E_trig^T bin'] The text states that IAA is consistent for gamma_direct and pi0 triggers 'within the same E_trig^T bin,' but the figure and surrounding text show different bins: 11 < E_trig^T < 15 GeV for pi0+jet and 15 < E_trig^T < 20 GeV for gamma_direct+jet. Please clarify whether a common trigger-energy bin is used, or correct the text to say that the comparison is made for the highest measured bin of each trigger. As written, the trigger-comparison claim is internally inconsistent and cannot be evaluated.
  3. [§3 (overall), Figs. 2–5] The manuscript reports fully-corrected results and physical interpretations but provides no numerical values, no uncertainty tables, no correction details, and no analysis of its own; all central plots are reproduced from Refs. [5], [17], and [19]. If this is intended as a research article, it is not self-contained. If it is a proceedings summary, that scope should be stated explicitly in the abstract and introduction, and the figures should be labelled as reproduced from those references with a note that the definitive results appear there.
minor comments (5)
  1. [Abstract and §3 intro] In the full text, 'Inp+Au collisions' on page 2 is missing a space; there are also several places where mathematical symbols run into surrounding text (e.g., '√sNN' is used without a separating space before '=').
  2. [Eq. (1)] The phrase 'which compared jet yield measured in central collisions' should read 'which compares the jet yield measured in central collisions'; the current wording is grammatically incomplete.
  3. [Fig. 1 and Ref. [1]] Figure 1 is labelled as taken from Ref. [1], but Ref. [1] is a Universe article on di-hadron correlations, not a STAR detector paper; the authors should cite the appropriate STAR detector publication or the original source of the 3D model.
  4. [§3.1, Fig. 2] The statement that 'the absence of a strong pT dependence in jet RCP contrasts with the more pronounced pT dependence observed for charged hadrons' would be clearer with an explicit statement of the pT range over which the comparison is made, since the hadron RCP data are shown only over a limited range.
  5. [Reference list] Ref. [17] is listed as arXiv:2309.00145 without noting whether it has since been published in a journal; if it has, the published citation should be given. Also, the reference list uses inconsistent formatting for collaboration names and journal titles.

Circularity Check

0 steps flagged · score 0.0 of 10

No circularity: the paper reports previously published STAR measurements through standard ratio observables; the terse BBC event-activity validation is a support gap, not a circular step.

full rationale

This proceedings paper summarizes STAR jet measurements taken from Refs. [5], [17], and [19]. The central observables RCP, RAA, and IAA are defined by ratio formulas that compare data yields, and no parameter is fitted and then relabeled as a prediction. The Au+Au suppression result is a direct experimental observation, and the comparison to theory uses external models (Hybrid, LBT, LIDO, SCET, NLO pQCD) with stated assumptions; there is no derivation chain in which an output is fed back into its own input. The p+Au conclusion, that high-EA suppression reflects an anti-correlation between event activity and the hard scale rather than quenching, is imported from the same collaboration's earlier measurement, Ref. [19]. This is a self-citation in the sense that a STAR author is summarizing STAR results, but it is not circular reasoning: the cited measurement is an independent, falsifiable dataset, not an unverified premise, and the present paper performs no new fit that would force the conclusion. The manuscript's weakest point is the single-sentence validation of the BBC ADC event-activity proxy in Sec. 3.3: 'Despite detector signal saturation effects, correlations between EA measured by the BBC and midrapidity charged particle density confirm the suitability of this method.' That sentence is a limitation of support and a correctness risk if the proxy is biased, but it is not an instance of a quantity being defined in terms of itself or a prediction reducing to its fit. No circular step can be exhibited from the paper's equations or citation structure, so the appropriate finding is no significant circularity.

Assumptions & free parameters 0 free parameters · 4 assumptions · 0 invented entities

The paper introduces no fitted parameters and no new entities. Its experimental results depend on standard analysis choices and on the validity of the referenced STAR reconstructions. The four axioms listed are the load-bearing assumptions that are stated but not derived in this summary.

assumptions (4)
  • domain assumption Glauber model estimates of ⟨N_coll⟩ for central and peripheral Au+Au collisions
    Used in Equations (1) and (2) to scale jet yields for R_CP and R_AA; the summary does not state the model uncertainties or centrality bin values.
  • domain assumption PYTHIA 6.428 with Perugia 2012 tune and CTEQ6L1 PDFs is a valid p+p reference for R_AA
    The R_AA denominator in Figure 3 is the PYTHIA-calculated inclusive charged-particle jet spectrum; the summary does not validate the tune or the scale of the reference uncertainty.
  • domain assumption Mixed-event background subtraction removes the underlying event in Au+Au semi-inclusive recoil jet measurements
    Section 3.2 states mixed-event techniques are used, but gives no detail on normalization, residual background, or closure tests; the I_AA result depends on this subtraction.
  • domain assumption BBC ADC sum in the Au-going direction, after saturation corrections, is a valid event-activity proxy for p+Au
    Section 3.3 uses BBC ADC sum to define high and low event activity; the claim that suppression is an EA-hard-scale correlation rather than quenching rests on this proxy being unbiased.

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Cite this review

Pith. "Pith review of Production of Jets at STAR." pith.science (2026). https://pith.science/paper/ZR6JLCTO

@misc{pith2026250723471,
  author       = {Pith},
  title        = {Pith review of: Production of Jets at STAR},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/ZR6JLCTO}},
  note         = {Machine review of arXiv:2507.23471}
}
abstract

Jets serve as an important tool to probe QCD both in the vacuum and in the hot and dense medium. The STAR experiment at RHIC plays a key role in studying QCD phenomena across different collision systems ($p$+$p$, $p$+A, A+A), offering access to a kinematic regime that complements that of the LHC. Building on recent jet and event activity studies at STAR, we present recent measurements on charged-particle jets at $\sqrt{s_{\mathrm{NN}}}~=~200$ GeV. In $p$+Au collisions, we explore event activity (EA) measured in the Au-going direction and its correlation with particle production at mid-rapidity. While soft particle production increases with EA, high-$p_{\mathrm{T}}$ jets are found to be inversely related to EA. Ratios of $p_{\mathrm{T}}$ imbalance and azimuthal dijet separation between high- and low-EA events show no significant differences, suggesting no strong evidence of jet quenching in high-EA $p$+Au collisions. In Au+Au collisions, we report semi-inclusive measurements of jets recoiling from $\gamma$ and $\pi^0$ triggers, using mixed-event techniques to subtract background and study jet suppression, intra-jet broadening, and acoplanarity. Additionally, we present inclusive charged-particle jet spectra corrected for background fluctuations, extending the kinematic reach of previous measurements. These results provide crucial insight into the modification of jets in the medium and contribute to a deeper understanding of QCD in heavy-ion collisions.

Figures

Figures reproduced from arXiv: 2507.23471 by the authors.

Figure 1
Figure 1. STAR detector and its sub-detectors. Taken from Ref. [1]. [PITH_FULL_IMAGE:figures/full_fig_p002_1.png] view at source ↗
Figure 2
Figure 2. presents a comparison of RCP for charged-particle jets with R = 0.2 and R = 0.3 in Au+Au collisions at √ sNN = 200 GeV to measurements from Pb+Pb collisions at √ sNN = 2.76 TeV [2], as well as to RCP for inclusive charged hadrons at both RHIC [3] and the LHC [4]. In central collisions, significant suppression of charged-particle jet yields is observed, reaching values around RCP ∼ 0.5, largely independent of jet pT.… view at source ↗
Figure 3
Figure 3. presents a comparison of the measured charged-particle jet RAA to various theoretical calculations. The reference distribution is given by the inclusive charged-particle jet spectrum in p + p collisions at √ s = 200 GeV, as calculated using PYTHIA Monte Carlo generator version 6.428 [6], with the Perugia 2012 tune (370) and CTEQ6L1 LO parton distribution functions [7]. The Hybrid [8], LBT [9], and LIDO [11, 10] mode… view at source ↗
Figures from the paper (2 more)
Figure 4
Figure 4. Figure 4: The IAA of semi-inclusive recoil jet distributions in central Au+Au collisions at √ sNN = 200 GeV shown for both γdir and π 0 triggers, with R = 0.2 and R = 0.5. The uncertainty bands reflect the correlated uncertainties in both the numerator and denominator. The dark …
Figure 5
Figure 5. Figure 5: Jet spectra per trigger for the trigger-side ( [PITH_FULL_IMAGE:figures/full_fig_p006_5.png]

Discussion (0). Continue with ORCID to comment.

Reference graph

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