{"id":"bcc1ffcf-c3b5-4381-8cf3-2ea39190274d","arxiv_id":"2501.18683","paper_version":2,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":7.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":4,"one_line_summary":"Hybrid Model simulations show ATLAS large-radius jet data rule out fully coherent jet energy loss, and low-pT jet-shape observables can visualize merging subjet wakes.","lead":"This paper uses simulations of jets in quark-gluon plasma to argue that new ATLAS measurements of large-radius jets made of skinny subjets rule out the idea that a whole jet loses energy as a single coherent object. It then proposes new ways to see the soft wake of particles a jet leaves behind, potentially turning jet wakes into a directly measurable signal.","discovery_kind":"new_application","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The Lres=∞ exclusion rests on a single hand-calibrated value of κsc with no refit or uncertainty band, so 'rule out any picture' is stronger than the evidence; a κsc scan is needed.","rationale":"The reader identifies the energy-loss formula Eq. (2.2) and the ISR treatment as the weakest assumptions. My stress-test converges on a more specific and more directly testable form of the same concern: the Lres=∞ exclusion is established only for a single point-calibrated κsc, with no marginalized uncertainty and no refit against the very observables used for the exclusion. The paper explicitly flags this limitation in Sec. 4, so the manuscript itself supports softening the 'rule out any picture' language to a statement about the Hybrid Model implementation. The wake-shape part of the paper is explicitly labeled non-quantitative (Sec. 6), so it is not the load-bearing claim. Since the reader's verdict is already CONDITIONAL and my concern reinforces rather than changes that conditionality, no change to the verdict is needed, but the manuscript should be revised to soften the exclusion claim and, ideally, to include the κsc-scan or a clear statement that the exclusion is only within the single-calibration model.","tokens_in":44363,"tokens_out":4936,"duration_ms":54694,"concrete_test":"Refit the Lres=∞ scenario by scanning κsc over a physically motivated range (for instance 0.3–0.8) and computing a chi-square or likelihood against the ATLAS R=0.2 jet, R=1 single-subjet, R=1 multi-subjet, and ΔR12-differential RAA data from Ref. [30], including EPS09 nPDF replicas. If any κsc yields acceptable agreement for all these observables simultaneously, the manuscript's statement that the data rule out Lres=∞ should be softened to 'the Hybrid Model with the chosen κsc=0.5 is disfavored'; if no κsc in the range can reproduce the multi-subjet suppression while keeping the single-subjet and R=0.2 predictions within systematics, the exclusion concern is resolved and the central claim stands.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The central claim is that ATLAS RAA data rule out Lres=∞, i.e., any picture in which an entire parton shower loses energy coherently as a single colored object (Abstract; Sec. 4, Figs. 1 and 3). The load-bearing step is the calibration of the Lres=∞ model: κsc=0.5 is set by requiring inclusive R=0.4 anti-kT jet suppression to coincide with the Lres=0 and Lres=2/(πT) cases around pT∼100 GeV (Sec. 3.1, Ref. [37]). No uncertainty on this calibration is propagated into the green bands, no refit including the ATLAS large-radius-jet observables is performed, and nPDF uncertainties are not varied. The paper itself acknowledges that 'quantifying the constraints on Lres implied by comparisons between Hybrid Model calculations and experimental data requires refitting the value of κsc as well as incorporating the uncertainties in the nPDFs' and leaves this Bayesian study to future work (Sec. 4). Because κsc is a free parameter of the excluded model, and because the claim is framed as ruling out 'any picture' rather than 'the Hybrid Model with κsc=0.5', the exclusion is not yet established. The associated ISR assumption in Appendix A is less problematic: it is explicitly tested and only makes Lres=∞ slightly more suppressed, so it does not carry the exclusion by itself. What carries the exclusion is the absence of a demonstrated parameter region for Lres=∞ that can describe the multi-subjet RAA while preserving agreement with the single-subjet and R=0.2 measurements. If a larger κsc or a modified coherent energy-loss functional can do so, the headline conclusion fails.","agreement_with_reader":"partial"},"referee_report":{"model":"deepseek-v4-flash","summary":"This paper uses the Hybrid strong/weak coupling model to analyze ATLAS measurements of large-radius jets reconstructed from skinny R=0.2 subjets in Pb+Pb collisions. The authors compute R_AA for such jets for three choices of the QGP resolution length, Lres = 0, 2/(πT), and ∞, and compare with the published ATLAS data as a function of jet pT and of the angular separation ΔR12 between subjets. They find that Lres = 0 and Lres = 2/(πT) reproduce the qualitative ordering and rough magnitude of the data, while Lres = ∞ predicts too little suppression for multi-subjet jets; they conclude that the data rule out any picture in which an entire parton shower loses energy coherently as a single colored object. In the second half of the paper, for γ-jet events they introduce a new two-dimensional differential jet shape observable adapted to R=2 jets with two skinny subjets, and use it to show that the soft hadrons from the wakes of two subjets merge into a single broad wake until the subjet rapidity separation exceeds Δy12 ~ 1.2-1.4, after which two sub-wakes become visible. They argue that restricting the observable to hadrons with 0.7 < pT < 1.0 GeV provides an experimentally accessible proxy for the wake shape.","tokens_in":44677,"tokens_out":4041,"duration_ms":40853,"significance":"If the central Lres = ∞ exclusion were established, the paper would provide a sharp, data-driven statement that the QGP resolves substructure within a parton shower, strengthening the case for using jet substructure as a quantitative probe of the medium. The wake-visualization observables in Section 5 are new and potentially impactful, and the authors are appropriately cautious there, explicitly noting that the analytic wake formula Eq. (2.4) is oversimplified, that radial flow is not included, and that their predictions are qualitative rather than quantitative. The paper is clearly written, does a service by reproducing the ATLAS selection in a public-style model setup, and includes useful appendices on ISR effects and on the distorting role of negative wakes in inclusive jet events. However, the headline claim in the abstract is stronger than what the analysis actually demonstrates, because the Lres = ∞ prediction is evaluated at a single hand-calibrated value of the strong-coupling parameter κsc with no propagated uncertainty or scan over that parameter.","major_comments":[{"comment":"The claim that ATLAS data rule out Lres = ∞ is load-bearing, but the Lres = ∞ prediction is evaluated at a single hand-calibrated value κsc = 0.5, set in Sec. 3.1 by requiring inclusive R = 0.4 jet suppression to match the other Lres choices near pT ~ 100 GeV. No uncertainty band from κsc or from nPDF variations is propagated into the green bands in Figs. 1 and 3, and no refit that includes the ATLAS large-radius-jet observables is performed. Since κsc is a free parameter of the excluded model, the comparison demonstrates only that Lres = ∞ with this calibration fails to describe the data; the abstract's wording that the data rule out 'any picture' in which an entire parton shower loses energy coherently is stronger than the evidence. The paper itself acknowledges in Sec. 4 that quantifying constraints on Lres requires refitting κsc and incorporating nPDF uncertainties; that refit, or at least a scan over κsc, is needed before the exclusion can be regarded as established.","section":"Sec. 4 (Figs. 1 and 3); Sec. 3.1"},{"comment":"The exclusion is also model-dependent because the energy-loss rate used for each parton is the holographic N = 4 SYM formula Eq. (2.2) with a universal fitted κsc. If this rate, or its scaling with color charge and distance, is not a good approximation for QCD partons in QGP, then the difference in RAA between single- and multi-subjet jets cannot by itself be used to infer that the medium resolves subjet structure. The paper tests only the Hybrid Model; the conclusion should therefore be framed as ruling out Lres = ∞ within this model class, unless the authors provide an argument that the qualitative failure of the Lres = ∞ scenario is insensitive to the choice of energy-loss formula.","section":"Sec. 2.1, Eq. (2.2)"}],"minor_comments":[{"comment":"The word 'cohrently' in the sentence describing Lres = ∞ should be corrected to 'coherently'.","section":"Introduction, p. 4"},{"comment":"The list of resolution lengths is written as '0, 2 π/T, and ∞'; this should be '0, 2/(πT), and ∞' to avoid ambiguity with 2π/T.","section":"Sec. 3.1"},{"comment":"The left-most bin, which denotes single-subjet jets, is placed arbitrarily at ΔR12 = 0.1; the caption should state explicitly that this is an arbitrary placement and not a measured value.","section":"Fig. 3 caption"},{"comment":"Refs. [116] and [130] are the same paper by K. Zapp; they should be merged into a single reference with appropriate cross-referencing.","section":"References"},{"comment":"The vertical scales in panels (a) and (b) of Fig. 4 differ by roughly two orders of magnitude; a sentence in the caption noting this difference would help the reader appreciate the relative size of the wake contribution.","section":"Sec. 5.1, Fig. 4"}],"recommendation":"major_revision","confidential_remarks":"The paper is within the scope of JHEP and is likely to be of interest to the heavy-ion jet-quenching community. The wake-shape study is novel and carefully caveated, but the central Lres = ∞ exclusion is currently supported only at a single calibration point and is framed too strongly. A κsc scan or a Bayesian refit including nPDF uncertainties, or a suitably weakened statement of the conclusion, would make the paper publishable. I do not see a load-bearing error that would require rejection; the issue is fixable within the manuscript's scope."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Two things to know. The genuinely new piece is the (r,r⊥) jet-shape observable for two-subjet wakes in Sec. 5; that is a clean idea, well matched to the ATLAS skinny-subjet selection, and likely to be picked up by experimentalists. The RAA-vs-ΔR12 calculation in Sec. 4 is also new and useful. The headline claim—that published ATLAS data rule out Lres=∞—is plausible within the Hybrid Model but not established as stated.\n\nCredit where due: the paper is careful and self-aware. The authors reproduce the qualitative ordering of the ATLAS results, and the pattern (multi-subjet jets much more suppressed, flat RAA vs ΔR12 for resolved subjets) is the right kind of evidence that the medium resolves subjet structure. The ISR analysis in App. A is a real attempt to kill the residual Lres=∞ suppression, and it works. They also state plainly that the wake-shape predictions are not quantitative (Eq. (2.4) is oversimplified, acknowledged), and that a Bayesian refit of κsc and nPDFs is needed.\n\nThe soft spot is the strength of the exclusion claim. The Lres=∞ band uses κsc=0.5, calibrated by matching R=0.4 jet suppression at one pT. No uncertainty is attached to that calibration, no refit includes the ATLAS large-radius observables, and nPDF uncertainties are not varied. The paper itself says the constraints require a refit. With one free model parameter un-scanned, 'these data are inconsistent with any picture' outruns the evidence. What the data show is inconsistency with this model at this parameter point. The stress-test note is right: a κsc scan, or at least a demonstration that reasonable variations can't rescue Lres=∞, is needed before the strong wording stands.\n\nMinor: no code or data tables are released. For a paper with this much simulation machinery, that hurts reproducibility. The wake-shape section is theory-internal; the experimental proxy should be treated as suggestive, not as a quantitative prediction.\n\nWho should read this: heavy-ion jet-quenching phenomenologists, and experimentalists planning substructure and medium-response measurements. It deserves a serious referee. My recommendation to the editor: send it to review, and ask for softened language on the exclusion plus a parameter scan. The qualitative physics—finite resolution length, subjet-resolved energy loss—probably survives; the 'any picture' framing doesn't.","headline":"New two-subjet wake-shape observable is the real contribution; the Lres=∞ exclusion is plausible but overstated, needing a κsc scan before 'rule out any picture'.","tokens_in":45324,"tokens_out":2445,"would_cite":true,"duration_ms":25594,"reading_group":"yes","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":[],"model":"deepseek-v4-flash","headline":"This paper argues that published ATLAS data on large-radius jets reclustered from skinny subjets rule out the possibility that quark-gluon plasma sees an entire parton shower as one coherent colored object, and introduces a soft-hadron…","keywords":["jet quenching","quark-gluon plasma","resolution length","large-radius jets","jet substructure","jet wakes","jet shapes","heavy-ion collisions"],"falsifier":"Measure RAA for large-radius jets with exactly two skinny subjets as a function of their angular separation with much smaller uncertainties, for example using R=0.1 subjets down to ΔR12 ~0.1–0.2; if the measured suppression of multi-subjet jets matches the flat Lres=∞ prediction, the central claim fails. Alternatively, if a soft-hadron jet shape around two subjets separated by Δy12<1.0 already shows two separated peaks, the predicted single broad wake is wrong.","tokens_in":44095,"feed_emoji":"🌊","tokens_out":5559,"duration_ms":48650,"temperature":0.7,"pith_summary":"The paper uses Hybrid Model simulations to show that the ATLAS measurement of suppression of large-radius R=1 jets built from R=0.2 subjets is incompatible with an infinite resolution length Lres=∞, meaning the quark-gluon plasma must resolve individual hard structures within a parton shower. With Lres=0 or a finite Lres=2/(πT), the model reproduces the ordering and magnitude of RAA for single- versus multi-subjet jets, with current data mildly favoring the finite value. The paper then constructs a new differential jet shape observable for R=2 jets with two skinny subjets in photon-jet events, built in coordinates aligned with the two subjets, and shows that wake hadrons form a single broad cloud until the subjets are separated by Δy12 ~1.2–1.4 in rapidity, after which two distinct sub-wakes appear. Using only hadrons with 0.7<pT<1.0 GeV makes this wake shape visible in an experimentally realistic way. A sympathetic reader would care because these results connect jet quenching to the microscopic resolution scale of the QGP and give a direct way to image the wake a jet leaves behind.","feed_headline":"ATLAS data rule out whole-shower jet quenching","feed_subtitle":"A finite resolution length reproduces the measured jet suppression; soft hadrons reveal two wakes only beyond Δy ≈ 1.2.","key_machinery":"The carrier of the argument is the Hybrid Model's resolution length Lres, the length scale below which two partons from the same splitting lose energy as one unresolved color charge. Energy loss follows the holographic strongly coupled formula dE/dx = -(4/π) Ein/xstop * $x^{2}$/$xstop^{2}$ / $\\sqrt$(1-(x/xstop)^2), with a single fitted κsc; wake hadrons come from the analytic Cooper–Frye expression Eq. (2.4). The new observable is a jet shape ρ(r,r⊥) defined in coordinates whose origin is the higher-pT subjet and whose r-axis points to the lower-pT subjet, so the region between the two subjets is resolved; restricting to 0.7<pT<1.0 GeV isolates the wake contribution.","core_discovery":"The central claim the authors are trying to establish is that the quark-gluon plasma resolves hard partonic substructure within jets: an entire parton shower does not lose energy coherently as a single colored object. In the Hybrid Model, reproducing the measured suppression of large-radius jets requires a finite QGP resolution length Lres, either zero or ~2/(πT), while Lres=∞ badly fails to describe the ATLAS data. The same setup reveals that two skinny subjets, even when well separated by 0.8–1.0 radians, excite a single common wake in the medium; only at separations Δy12 ≳ 1.2–1.4 do two separate sub-wakes emerge, and this merging can be visualized with soft hadrons of pT between 0.7 and 1.0 GeV.","pith_inferences":["Editorial inference: the wake-merging threshold may shift with radial flow, which is known to harden and collimate wake hadrons; a more complete event-by-event wake treatment could move the separation point from ~1.4 to closer to ~1.0.","Editorial inference: the same two-subjet shape observable could be measured in inclusive jet events, but negative wakes from away-side jets will distort it; imposing a rapidity gap between the selected jet and recoiling jets should mitigate that distortion.","Editorial inference: pushing the angular resolution to ΔR12 ~0.1–0.2 with R=0.1 subjets could directly connect the resolution-length picture to perturbative QCD color-coherence predictions, offering a cross-check between strong-coupling and weak-coupling descriptions."],"forward_implications":["If Lres=∞ is excluded, then any model that treats an entire parton shower as a single coherent energy-loss source cannot describe the measured suppression of large-radius jets with multiple skinny subjets.","The QGP resolves hard partonic substructure within jets, so the total energy loss of a jet scales with the number of resolved quenched structures it contains.","The new soft-hadron jet shape observable should show a single common wake cloud until Δy12 ~1.2–1.4, then two separated wakes, providing a direct experimental image of jet wakes.","Measurements using skinnier R=0.1 subjets to reach angular separations ΔR12 ~0.1–0.2 could distinguish Lres=0 from Lres=2/(πT), where the predictions differ most.","A full Bayesian refit including κsc and nuclear PDF uncertainties is needed to determine the optimal value of Lres rather than just excluding Lres=∞."],"supporting_citations":[{"why":"Supplies the ATLAS RAA data and the skinny-subjet reclustering strategy that the paper reproduces and extends.","marker":"[30]"},{"why":"Introduces the Hybrid Model framework that combines a perturbative QCD shower with strongly coupled energy loss.","marker":"[32]"},{"why":"Provides the analytic wake-hadron spectrum, Eq. (2.4), used to construct all wake shapes in the paper.","marker":"[34]"},{"why":"Defines and implements the QGP resolution length Lres in the Hybrid Model, the key parameter under study.","marker":"[35]"},{"why":"Supplies the fitted κsc values used for Lres=0 and Lres=2/(πT).","marker":"[36]"},{"why":"Establishes the connection between jet substructure modification and Lres, and sets κsc=0.5 for Lres=∞.","marker":"[37]"},{"why":"Gives the formation-time assignment τ=2E/Q^2 that endows the parton shower with its spacetime structure.","marker":"[31]"},{"why":"Supplies the holographic strongly coupled energy-loss rate used in Eq. (2.2).","marker":"[89, 90]"},{"why":"Shows that the fraction of subjets originating from initial-state radiation increases with separation, explaining the residual Lres=∞ suppression.","marker":"[116]"}],"fun_headline_variants":["ATLAS: QGP resolves jet substructure, not whole showers","Jet wakes merge until subjets split beyond Δy≈1.2","Single wake for subjets 1 rad apart; two only beyond 1.2","QGP sees jet parts individually—no coherent shower loss","Subjets expose wake shape: one wake until Δy>1.2"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The load-bearing premise is that the holographic strongly coupled energy-loss formula with a universal fitted κsc describes how each parton loses energy in QGP, and that this rate determines how the number of resolved color charges changes with Lres.","fun_headline_variants_meta":{"raw":{"variants":["ATLAS: QGP resolves jet substructure, not whole showers","Jet wakes merge until subjets split beyond Δy≈1.2","Single wake for subjets 1 rad apart; two only beyond 1.2","QGP sees jet parts individually—no coherent shower loss","Subjets expose wake shape: one wake until Δy>1.2"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000748,"raw_usage":{"total_tokens":3411,"prompt_tokens":1101,"completion_tokens":2310,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":717,"completion_tokens_details":{"reasoning_tokens":2214}},"tokens_in":717,"tokens_out":2310,"duration_ms":15510,"temperature":1.0,"reasoning_tokens":2214,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-09T22:51:17.028770+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Measure RAA for large-radius jets with exactly two skinny subjets as a function of their angular separation with much smaller uncertainties, for example using R=0.1 subjets down to ΔR12 ~0.1–0.2; if the measured suppression of multi-subjet jets matches the flat Lres=∞ prediction, the central claim fails. Alternatively, if a soft-hadron jet shape around two subjets separated by Δy12<1.0 already shows two separated peaks, the predicted single broad wake is wrong.","supporting_citations":[{"cited_title":"The role of initial state radiation in quenched jets","cited_arxiv_id":"2208.00813","evidence_quote":"Shows that the fraction of subjets originating from initial-state radiation increases with separation, explaining the residual Lres=∞ suppression."}],"review_version":1}