{"id":"892cee47-b652-415e-8847-534b112b5f53","arxiv_id":"2501.03419","paper_version":3,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":6.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":0,"one_line_summary":"Predicts that the rapidity asymmetry of jet-hadron correlations in di-jets with a rapidity gap is a background-free observable for the jet-induced diffusion wake.","lead":"This paper proposes a new way to spot the 'diffusion wake', a trail of depleted particles left by a fast jet moving through the quark-gluon plasma, using pairs of jets separated in rapidity. The method uses abundant di-jet events instead of rare Z-jet events and is claimed to need no background subtraction.","discovery_kind":"new_method","skeptic_critique":{"model":"deepseek-v4-flash","headline":"Background-free claim rests on an untested cancellation: the p+p and MPI/underlying-event baselines are assumed independent of the di-jet rapidity gap, but the paper's own beam-remnant asymmetry suggests gap-dependent contamination.","rationale":"The paper's main contribution is a proposed observable and a CoLBT-hydro prediction. The strongest claim is that the rapidity asymmetry is 'robust and background-free.' For that claim to hold, the difference in medium-modified correlations between large and small rapidity-gap bins must be free of contributions from the p+p baseline and from selection-dependent underlying-event/bulk effects. The authors assert this in Sec. 3 ('backgrounds... are the same... will be completely canceled') but no calculation is shown to support it. In fact, the paper itself notes a p+p asymmetry caused by beam-remnant interference; whether that remains exactly independent of the sub-leading jet rapidity is not demonstrated, and acceptance cuts plus MPI/hydro longitudinal flow can introduce gap-dependent contributions. Therefore the most load-bearing concern is the untested background-cancellation assumption. The concrete null test — computing the asymmetry with jet-medium coupling off or in p+p alone — would settle it. If the residual baseline is nonzero at the signal level, the central claim is weakened; if it is zero, the observable is as robust as claimed. Since the paper still provides a plausible proposal with model predictions, and the issue is testable rather than demonstrably false, the appropriate verdict remains conditional. This matches the reader's assessment, so no change to the verdict is needed.","tokens_in":10831,"tokens_out":9588,"duration_ms":100666,"concrete_test":"Run the same CoLBT-hydro analysis with jet-medium interactions disabled (or with p+p events) and identical selection: fixed leading-jet pT/rapidity, pT2 > 90 GeV/c, and the same three gap bins. Compute the null asymmetry ΔN_null = N(large gap) − N(small gap) in this background-only sample, with the same rapidity shifts and normalizations. If this null asymmetry is nonzero at the level of the diffusion-wake signal in Figs. 3(c,d), the 'background-free' claim fails. Additionally, repeat the mixed-event subtraction using a background built from events in the opposite gap bin; a stable result would support cancellation, whereas a shift would show gap-dependent backgrounds.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The central claim is that the rapidity asymmetry is 'background-free,' asserted in Sec. 3 because, for fixed leading-jet rapidity, backgrounds from bulk hadron production and MPI are the same for different di-jet rapidity gaps and thus cancel in ΔNAA(gap) − ΔNAA(ref). This cancellation is not demonstrated and is not obviously true. First, the p+p baseline is not shown to be gap-independent: the paper itself notes an intrinsic p+p Δη asymmetry from interference with beam remnants, and that interference should depend on the sub-leading jet's rapidity relative to the beam. Since the observable is defined through a double difference that subtracts p+p, any gap dependence in N_pp enters directly. Second, the event selection itself changes with the gap: requiring a large |Δη_jet1,jet2| with fixed η_jet1 pushes the sub-leading jet toward the edge of the acceptance and changes the sampled MPI/underlying-event activity and, in A+A, the longitudinal flow profile sampled by the sub-leading jet. The theoretical-background subtraction removes only the hydro bulk, not these selection-dependent terms. Figures 3(c,d) show a signal of order ±0.5, but no null test is shown to establish that the residual baseline is below that level.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"The paper proposes a new observable for the jet-induced diffusion wake in heavy-ion collisions: the rapidity asymmetry of jet-hadron correlations in di-jet events, defined as the difference between the medium-modified correlation for a large di-jet rapidity gap and that for a small gap. Using the CoLBT-hydro model with PYTHIA8 di-jet initial conditions, the authors compute this asymmetry for central Pb+Pb collisions at 5.02 TeV, both with a theoretical hydro background subtraction and with a mixed-event subtraction. They find a negative dip in the rapidity region of the shifted diffusion wake and a positive bump in the region of the reference jet, with the separation growing with the gap. The central claim is that this asymmetry is a robust and background-free signal because bulk and MPI backgrounds cancel when the leading-jet rapidity is fixed and only the sub-leading-jet rapidity gap is varied.","tokens_in":11059,"tokens_out":5824,"duration_ms":57311,"significance":"If validated, the proposed asymmetry would give experimentalists a practical observable for studying the diffusion wake in di-jet events, which are far more abundant than Z/γ-jet events at the LHC and would complement recent CMS and ATLAS observations. The predictions are concrete and falsifiable: the sign, magnitude, and gap dependence of the asymmetry are specified, and two independent background-subtraction procedures are presented. A clear strength is that the CoLBT-hydro model parameters were calibrated in earlier work and no parameter is fitted to the asymmetry itself; the processed data are also made available. The main caveat is that the background-free property and the symmetrization convention are asserted rather than demonstrated, and no statistical uncertainties are shown, so the strength of the central claim currently exceeds the evidence presented.","major_comments":[{"comment":"The statement that the rapidity asymmetry is background-free is asserted rather than demonstrated. The cancellation requires that, for fixed leading-jet rapidity, the uncorrelated background from bulk hadron production and MPI is identical for different di-jet rapidity gaps. This is not obvious because the event selection itself changes with the gap: for a fixed η_jet1, a large |Δη_jet1,jet2| pushes the sub-leading jet toward the edge of the acceptance, changing the sampled MPI/underlying-event activity and, in A+A, the longitudinal flow profile. The paper itself notes in the Fig. 4 discussion that the p+p correlation exhibits a rapidity asymmetry from interference with beam remnants; the claim that this p+p asymmetry is independent of the di-jet rapidity gap is not supported by any comparison of p+p gap bins. Since the observable is a double difference involving N_pp, any gap dependence in the p+p baseline enters directly. A null test using background-only events or a p+p-only asymmetry scan as a function of gap is needed to justify the background-free claim.","section":"Sec. 3 (background-free claim near Eq. (1) and Fig. 3(c,d))"},{"comment":"The reference distribution for the smallest gap is symmetrized by construction, so the asymmetry as defined isolates only the odd part of the large-gap distribution. The physical interpretation that the diffusion wake is shifted by the gap presupposes that the small-gap distribution would itself be symmetric, but the authors do not show the raw versus symmetrized small-gap ΔNAA. In addition, for the away-side correlations the distributions are shifted by the p+p away-side peak position for each gap; this per-gap shift changes the rapidity variable and can distort the asymmetry. The authors should quantify how much these choices affect the result and present the unshifted, unsymmetrized distributions for comparison.","section":"Sec. 3 (symmetrization of the reference distribution)"},{"comment":"No statistical uncertainties are shown for the Monte Carlo results, so the significance of the dip/bump structure, whose amplitude is of order ±0.5 in ΔNAA, cannot be assessed. Since the central claim is that the asymmetry is robust, the paper should provide statistical errors from the event samples and, ideally, a control calculation with the diffusion wake artificially suppressed or with a background-only sample to show that the observed asymmetry is not a baseline effect. Without such a null test, the word 'robust' is not supported by the presented evidence.","section":"Figs. 3(c,d) and 4(b)"}],"minor_comments":[{"comment":"The collision energy is given as √sNN = 5.2 TeV, while the text and abstract use 5.02 TeV; this typo should be corrected.","section":"Fig. 2 caption"},{"comment":"The integration limits over Δφ are not specified in the formula; the text refers to near-side (Δφ < π/2) and away-side (Δφ > π/2) regions, so the limits should be written explicitly in the equation.","section":"Eq. (1)"},{"comment":"The data availability statement links to a dataset titled 'single-jet diffusion wake,' which may be different from the di-jet correlation data analyzed here; the authors should clarify the link or provide the correct dataset reference.","section":"Reference [78]"},{"comment":"The terms 'same-hemisphere' and 'opposite-hemisphere' are used for ηjet1 ηjet2 > 0 and < 0, which is unconventional because 'hemisphere' usually refers to azimuthal angle; 'same-sign rapidity' or 'same-side in rapidity' would be clearer.","section":"Sec. 4 and Fig. 4"}],"recommendation":"major_revision","confidential_remarks":"The paper is within scope for a high-energy nuclear physics letter, and the model prediction is coherent and potentially useful. The main concern is that the background-free claim is central and currently rests on an untested cancellation assumption; this is fixable with additional calculations, so major revision rather than rejection seems appropriate. The self-citation pattern is consistent with the authors' long-standing model-development program and is not, in my view, problematic. Please also check the data availability link, which appears to point to a different dataset."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"The real content here is narrow but real. The rapidity-gap idea goes back to Pablos, and the diffusion wake itself was already established in Z/gamma-jet events. What is new is the explicit asymmetry construction -- large-gap minus small-gap medium-modified correlations -- plus its gap dependence and a first mixed-event feasibility study inside CoLBT-hydro. That is a useful package for experimentalists because di-jets are abundant. The model plots show exactly the advertised structure: a depletion on the diffusion-wake side and an enhancement on the reference-jet side, with the separation growing with the gap. The physics argument for why the asymmetry should appear is coherent, and the processed data are on Zenodo, which is good practice.\n\nThe soft spot is the word 'background-free'. In Sec. 3 the paper claims that for fixed leading-jet rapidity, the bulk and MPI backgrounds are the same for different gaps and cancel. That is an assumption, not a demonstration. The selection itself changes with the gap: requiring a larger |Delta_eta| pushes the sub-leading jet toward the acceptance edge and changes the sampled MPI activity and longitudinal flow profile. Those selection-dependent terms are not removed by the theoretical background subtraction, which only removes the hydro bulk. The paper's own mixed-event p+p result also shows an intrinsic asymmetry from beam remnants, and it is asserted to be gap-independent but no test is shown. So the asymmetry may well be dominated by the diffusion wake, but 'background-free' is over-sold. A null test -- e.g., the same asymmetry in p+p or in a background-only simulation -- would settle it.\n\nMinor issues: no error bars on any of the model curves, the small-gap reference is symmetrized by construction, and the data availability statement points to processed data but not the full raw set or the exact run parameters. None of this kills the idea. The central mechanism is plausible and the observable is measurable.\n\nWho should read this: experimentalists in heavy-ion jet correlation analyses, and theorists working on jet-medium response. It deserves a serious referee -- I would send it out. The referee should ask for a null/background-only check, uncertainties on the predictions, and a less absolute claim about being background-free. With those, this could be a solid contribution.","headline":"A genuinely useful observable for diffusion-wake searches in di-jet events, with model predictions that support the idea, but the 'background-free' claim is asserted rather than tested and should be softened.","tokens_in":11585,"tokens_out":1427,"would_cite":true,"duration_ms":16716,"reading_group":"yes","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":["25.75.-q","12.38.Mh"],"model":"deepseek-v4-flash","headline":"The paper proposes the rapidity asymmetry of jet-hadron correlations in di-jets with a rapidity gap as a background-free signal of the diffusion wake induced by jets in the quark-gluon plasma, and predicts it with the CoLBT-hydro model.","keywords":["diffusion wake","jet-hadron correlation","di-jet asymmetry","quark-gluon plasma","medium response","CoLBT-hydro model","rapidity gap","heavy-ion collisions"],"falsifier":"A background-only control—for example, running the same di-jet selection with jet-medium interaction switched off, or measuring the asymmetry in p+p collisions or peripheral A+A collisions where no wake forms—should show no gap-dependent asymmetry; if a depletion/enhancement pattern of comparable size survived there, the background-free claim would fail. Alternatively, high-statistics data could check whether the predicted dip appears at the rapidity position of the sub-leading jet and grows with the rapidity gap as CoLBT-hydro predicts.","tokens_in":10625,"feed_emoji":"💥","tokens_out":11057,"duration_ms":90232,"temperature":0.7,"pith_summary":"When a jet plunges through the quark-gluon plasma made in a heavy-ion collision, it leaves both a cone of enhanced soft particles and a rarer depletion behind it, the diffusion wake. In di-jet events that depletion is normally hidden under the soft-particle enhancement produced by the other jet, so the wake has so far been seen only in rare Z/γ-jet events. This paper argues that if the two jets are selected with a rapidity gap between them, the wake of the sub-leading jet shifts in rapidity away from the leading jet, producing a dip in the near-side rapidity correlation and an enhancement in the region that is no longer suppressed. The difference between large-gap and small-gap correlations, called the rapidity asymmetry, is claimed to be background-free because bulk and multiple-parton-interaction backgrounds cancel once the leading-jet rapidity is fixed. The authors predict the size and gap dependence of this asymmetry using the CoLBT-hydro model, providing an observable that abundant di-jet data at the LHC could measure without dedicated background subtraction.","feed_headline":"Di-jet rapidity gaps expose the quark-gluon plasma's wake","feed_subtitle":"Comparing di-jets with large and small rapidity gaps cancels backgrounds and exposes the wake's depletion dip.","key_machinery":"The central object is the rapidity asymmetry $\\Delta N_{AA}(\\Delta\\eta) - \\Delta N_{AA}(|\\Delta\\eta_{j_1j_2}|<0.5)$, where $\\Delta N_{AA}$ is the medium modification (Pb+Pb minus p+p) of the jet-hadron rapidity correlation projected on the near side ($\\Delta\\phi<\\pi/2$) or away side ($\\Delta\\phi>\\pi/2$) of the leading jet, and the small-gap distribution is symmetrized as the reference. The mechanism is the shift of the diffusion wake in rapidity: once the sub-leading jet is separated from the leading jet by a finite rapidity gap, the depletion that trails one jet no longer overlaps the enhanced soft-hadron ridge of the other, converting an overlap loss into a localized dip and a compensating enhancement. The engine that produces the prediction is the CoLBT-hydro model, which couples the Linear Boltzmann Transport parton shower to (3+1)-dimensional viscous hydrodynamics so that the concurrent evolution of the jets and the medium response is simulated; jet-hadron correlations are formed after either theoretical (same-hydro-event-without-jet) or mixed-event background subtraction.","core_discovery":"The paper's central claim is that the rapidity asymmetry of jet-hadron correlations in back-to-back di-jet events, defined as the difference between the medium modifications for large and small di-jet rapidity gaps, is a clean signal of the jet-induced diffusion wake in the quark-gluon plasma. In a di-jet with a small rapidity gap, the diffusion wake of one jet overlaps with the medium-enhanced soft-hadron ridge of the other jet, so it only reduces the enhancement. When the sub-leading jet sits at a finite rapidity gap, its diffusion wake is shifted in rapidity away from the leading jet, creating a net depletion (negative dip) in the near-side correlation in the rapidity region of the wake, while the reference region that is no longer suppressed by the wake shows an enhancement. Because the backgrounds from bulk hadron production and multiple parton interactions are the same for different rapidity gaps when the leading-jet rapidity is fixed, these backgrounds cancel in the asymmetry, making it measurable without event-by-event background subtraction. The CoLBT-hydro simulation predicts a visible dip whose amplitude and peak separation grow with the rapidity gap, both with theoretical background subtraction and with the mixed-event technique used in experiments.","pith_inferences":["One could test the background-free assumption directly by constructing the asymmetry from events with no reconstructed sub-leading jet but identical leading-jet selection; any residual gap-dependent asymmetry would signal contamination from acceptance or selection effects.","The gap dependence of the dip position encodes the wake geometry and could be inverted, in principle, to extract the plasma sound speed or transport coefficients, a step the paper does not take.","A similar but weaker depletion at large $\\Delta\\eta$ is expected for single-inclusive jets under mixed-event subtraction, which the paper mentions as a follow-up; this could provide a lower-cost cross-check in existing data.","Combining the di-jet asymmetry with Z-jet and γ-jet diffusion-wake measurements would allow systematic tests of whether the wake shape depends on the energy and flavor of the initiating parton, since the three channels probe different jet-energy scales."],"forward_implications":["The rapidity asymmetry can be measured directly with experimental di-jet data without event-by-event background subtraction, since bulk and MPI backgrounds cancel at fixed leading-jet rapidity.","The amplitude of the asymmetry and the separation between its depletion and enhancement peaks increase with the rapidity gap, so the gap dependence maps the position and strength of the diffusion wake.","Because di-jet events are far more abundant than Z/γ-jet events, this observable should give higher-statistics access to the diffusion wake than current CMS and ATLAS measurements.","The same asymmetry survives when the standard mixed-event background subtraction is used, so existing experimental analysis pipelines can apply the method directly.","For same-hemisphere di-jets the asymmetry is weaker but still present, extending the reach of the method to moderate rapidity coverage at RHIC and LHC."],"supporting_citations":[{"why":"First suggested that di-jets with a finite rapidity gap could expose the diffusion wake, which this paper turns into a specific asymmetry observable.","marker":"[35]"},{"why":"Predicted the diffusion-wake valley in the rapidity direction of γ/Z-jet correlations within CoLBT-hydro, establishing the imaging method adapted here to di-jets.","marker":"[58]"},{"why":"The CMS observation of the diffusion-wake valley in Z-hadron correlations that motivates searching for a more abundant di-jet signal.","marker":"[61]"},{"why":"Introduced the CoLBT-hydro model coupling LBT parton transport with hydrodynamic medium response, the simulation framework for the paper's predictions.","marker":"[31]"},{"why":"A further CoLBT-hydro model paper that supplies the jet-medium response simulation used for the correlation predictions.","marker":"[36]"},{"why":"Concurrent jet-hydro evolution implementation of CoLBT-hydro, referenced as part of the model employed for the event-by-event simulations.","marker":"[63]"},{"why":"Introduced the recombinatory background-subtraction technique that isolates the diffusion wake from medium-modified MPI backgrounds, the background problem this paper avoids by construction.","marker":"[57]"}],"fun_headline_variants":["Rapidity asymmetry in di-jets: clean wake signal","Di-jet rapidity gaps unmask diffusion wake","Jet wake probed via di-jet rapidity asymmetry","Background-free wake from di-jet rapidity gaps","Rapidity gap asymmetry exposes jet-induced wake"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The load-bearing premise is that for a fixed leading-jet rapidity, all uncorrelated backgrounds—bulk hadron production and multiple parton interactions—are identical for di-jet events with different rapidity gaps, so they cancel exactly in the rapidity asymmetry; the paper states this but does not test it with a background-only calculation.","fun_headline_variants_meta":{"raw":{"variants":["Rapidity asymmetry in di-jets: clean wake signal","Di-jet rapidity gaps unmask diffusion wake","Jet wake probed via di-jet rapidity asymmetry","Background-free wake from di-jet rapidity gaps","Rapidity gap asymmetry exposes jet-induced wake"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000492,"raw_usage":{"total_tokens":2502,"prompt_tokens":1110,"completion_tokens":1392,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":726,"completion_tokens_details":{"reasoning_tokens":1314}},"tokens_in":726,"tokens_out":1392,"duration_ms":11713,"temperature":1.0,"reasoning_tokens":1314,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-10T21:52:35.907119+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"A background-only control—for example, running the same di-jet selection with jet-medium interaction switched off, or measuring the asymmetry in p+p collisions or peripheral A+A collisions where no wake forms—should show no gap-dependent asymmetry; if a depletion/enhancement pattern of comparable size survived there, the background-free claim would fail. Alternatively, high-statistics data could check whether the predicted dip appears at the rapidity position of the sub-leading jet and grows with the rapidity gap as CoLBT-hydro predicts.","supporting_citations":[{"cited_title":"Wakes in the quark-gluon plasma","cited_arxiv_id":"hep-ph/0606316","evidence_quote":"Predicted the diffusion-wake valley in the rapidity direction of γ/Z-jet correlations within CoLBT-hydro, establishing the imaging method adapted here to di-jets."}],"review_version":1}