{"id":"9c462c4a-ee8b-45cd-a447-18bcfc48c3e8","arxiv_id":"2507.18790","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":5.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":6,"one_line_summary":"Subtracting the product of single-particle energy flows from the energy-energy correlator isolates genuine two-particle correlations in jets, as demonstrated with PYTHIA.","lead":"This paper shows that the standard jet 'energy-energy correlator' contains both uncorrelated pairs and genuine correlations, and proposes subtracting a constructed baseline to isolate the genuine part. The resulting ratio could help separate ordinary QCD splitting from medium effects in heavy-ion collisions.","discovery_kind":"new_application","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The heavy-ion double-ratio claim rests on an unproven cancellation of the medium response; even an uncorrelated, angle-independent response can shift the ratio through the trivial denominator, so the AA conclusions are not yet supported.","rationale":"The pp proposal is clearly stated, and the PYTHIA demonstration supports the existence of a nontrivial difference between the full EEC and the trivial EEC; that part of the paper is credible and does not warrant a stronger objection. The advertised heavy-ion payoff, however, depends on the cancellation of the medium response in the genuine correlation and in the double ratio. The paper asserts this cancellation based on the angular independence of the response, but the necessary condition is a factorization property of the two-particle density, not angular flatness. The reader's weakest assumption identifies exactly this unsupported premise, and I agree with that assessment. The concrete test above would settle whether the cancellation actually holds in a controlled setting; until such a test is performed, the conditional verdict is appropriate. No verdict change is needed relative to the reader's assessment.","tokens_in":10608,"tokens_out":18935,"duration_ms":222907,"concrete_test":"Run a controlled toy with PYTHIA jets from the 300-350 GeV bin of Fig. 3: add a medium-response energy flow R(theta)=R0 (and, as a second variant, a jet-angle-correlated form such as R(theta) proportional to 1+cos(theta)), normalized so the response carries a few percent of the jet energy. Recompute the full EEC and the jet-mixing trivial EEC with the same procedure as Eqs. (1), (7), and (8), and evaluate Eq. (12) against the no-response sample. If the double ratio shifts by more than the statistical uncertainty of the sample, the claimed cancellation of the medium response is disproven; if it is invariant, the assertion survives this test.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The least supported load-bearing step is the AA claim around Eq. (12): that the medium response cancels in the genuine correlations 'because the medium response has no particular angular dependence' (paragraph before the Conclusion). Cancellation in the difference Delta = full - trivial requires that all response-involving pair contributions factorize into single-particle densities, i.e. that the response is emitted independently of the jet and of itself. Angle-independence of the response single-particle distribution is neither necessary nor sufficient for this: a flat but jet-correlated response (e.g. a wake aligned with the jet) would survive in Delta. Moreover, even for an independent flat background, the ratio Eq. (10) divides by the trivial EEC, whose normalization (Ntrivial/Cmix) is chosen to match the full integral and therefore depends on the response; the response can shift the ratio and the double ratio Eq. (12) even when it cancels in the difference. The paper provides no analytic derivation and no AA Monte Carlo check; the PYTHIA demonstration only establishes the pp decomposition. Until the factorization property is demonstrated in a medium-response model, the heavy-ion extraction of the energy-loss fraction and splitting modification is unsupported.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"The paper proposes a decomposition of the in-jet energy-energy correlator (EEC) into a \"trivial\" part built from two independent single energy flows with respect to the jet axis and a \"genuine correlation\" remainder. The authors define the trivial correlator both as a convolution of single energy distributions (Eq. 7) and through a mixed-jet procedure (Eq. 8), demonstrate in PYTHIA pp events at several LHC jet energies that the full and trivial EECs differ, and present the difference (Eq. 9) and ratio (Eq. 10) as observables that expose genuine two-particle correlations at small and moderate/large angles. They further propose AA/pp double ratios (Eqs. 11-12) to isolate medium modification of parton splitting in heavy-ion collisions, arguing that the medium response cancels in the genuine correlations because it has no particular angular dependence. The pp analysis is the central new demonstration; the heavy-ion application is presented as a prediction rather than as a computed result.","tokens_in":10878,"tokens_out":11948,"duration_ms":130835,"significance":"If the pp decomposition is robust, the proposal offers a clearly defined, experimentally accessible jet-substructure observable that separates correlated from uncorrelated pair production and could sharpen the interpretation of EEC measurements in different kinematic regions. The paper has concrete strengths: the PYTHIA demonstration, the explicit mixed-jet algorithm, the comparison with a TMD-based model in Appendix B, and the clear statement of the observable definitions. The main weakness is that the heavy-ion claims rest on an unproven cancellation of the medium response; the paper provides no analytic calculation and no AA Monte Carlo check for that cancellation. The pp part of the paper is sound and publishable in principle, but the AA conclusions as currently stated go beyond what is demonstrated.","major_comments":[{"comment":"The claim that the medium response cancels in the genuine correlations in AA collisions is not established. Cancellation in the difference Δ = full − trivial requires that all response-involving pair contributions factorize into single-particle densities; \"no particular angular dependence\" of the response single-particle distribution is neither necessary nor sufficient (for example, a flat but jet-aligned wake would survive in Δ). Moreover, even if the response canceled in Δ, the ratio in Eq. (10) and the double ratio in Eq. (12) divide by the trivial EEC, whose normalization Ntrivial is set to match the full integral and therefore depends on the response; a response that only shifts the overall normalization can still change these ratios. The paper provides no analytic derivation and no AA Monte Carlo demonstration; the PYTHIA study is pp only. Until the factorization property is demonstrated in a medium-response model, the advertised extraction of the jet energy-loss fraction and the medium modification of parton splitting is unsupported.","section":"Paragraph before Conclusion; Eqs. (9)-(12)"},{"comment":"The two constructions of the trivial correlator are not obviously equivalent, and the equivalence is load-bearing for the subtraction in Eq. (9). Eq. (7) is a convolution of the angle-averaged single energy distributions and, as written, includes pairs drawn from the same original jet, including self-pairs (i=j) and genuine correlated pairs within a jet; the mixed-jet definition in Eq. (8) contains only pairs from different original jets. These same-jet terms are formally suppressed by 1/Njet, but the suppression is not stated or quantified. The paper should provide a derivation of the equivalence, or state the large-Njet approximation and estimate the correction, rather than only showing agreement in one pT bin in Fig. 5. Without this, the claimed isolation of genuine correlations is not fully pinned down.","section":"Section 'Trivial two particle distributions...', Eqs. (5)-(8)"}],"minor_comments":[{"comment":"The phrase \"genuine correlations exists\" should read \"genuine correlations exist\".","section":"Abstract"},{"comment":"The x-axis label \"-10L R\" appears to be a rendering artifact; it should read something like \"log10(RL)\".","section":"Figures 2 and 3"},{"comment":"The parameters c1, c2, and N in the TMD model are free parameters chosen to describe the same PYTHIA distribution; the text should state explicitly that these are fitted values, so the agreement is a description rather than an independent prediction.","section":"Appendix B, Eq. (B8) and Fig. 5"},{"comment":"The text states Ntrivial ≈ 0.85 and that it equals the integral of Eq. (1), but should explicitly note that this normalization is fixed by that equality, so the angular integral of the difference in Eq. (9) vanishes by construction and the ratio in Eq. (10) carries the shape information.","section":"Section 'Trivial two particle distributions...', Eq. (7)"},{"comment":"No statistical uncertainties are shown; since the ratio at large θ involves a ratio of two small quantities, adding error bars or stating that the curves are qualitative would strengthen the claims about the large-angle region.","section":"Figures 2 and 3"}],"recommendation":"major_revision","confidential_remarks":"The heavy-ion section is the weakest part of the manuscript; the cancellation claim for the medium response is stated as an expectation rather than demonstrated. The pp proposal is a reasonable contribution, and the mixed-jet construction is a useful practical element. I would suggest the editors encourage the authors either to provide a medium-response model check or to substantially soften the AA claims, since the abstract and conclusion currently present the cancellation as a firm result."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Zhao, Koch, and Yuan propose constructing a 'trivial' EEC from two independent single-particle energy flows, then look at the difference and ratio against the full EEC. That is a clean idea, and the PYTHIA demonstration for pp jets is convincing: the ratio REEC shows clear structure at small and moderate angles, with the expected energy dependence. The connected-versus-disconnected decomposition is textbook, but applying it to jet EEC with a well-defined jet axis and proposing the AA/pp double ratio is new. As a baseline subtraction observable for jet substructure, this will likely get used.\n\nThe soft spot is the heavy-ion part. The paper claims that medium responses cancel in the genuine correlation and double ratio because the medium response has no particular angular dependence, citing Ref. [47]. That argument is not made. Angle-independence of the response single-particle distribution is neither necessary nor sufficient for the response contribution to factor into a product of single flows; a flat but jet-correlated wake survives in the difference. And even a fully factorized, angle-independent response shifts the ratio, since the trivial denominator is normalized to match the full integral. So the extraction of jet energy loss fraction and splitting modification from Eq. (12) is unsupported. This is not a minor caveat; it is the load-bearing claim for why the double ratio is meaningful in AA. The paper would need an analytic model or a medium-response Monte Carlo (e.g., JEWEL or a thermal wake) to show the factorization.\n\nMinor issues: Ntrivial is fitted to match the full integral, so the ratio is shape-only; fine for the pp demonstration but worth noting in interpretation. The TMD comparison in Appendix B is a fit with parameters c1, c2, N, not a prediction, so it adds little.\n\nVerdict: the pp core is sound and publishable as a method proposal; the AA claims should be reframed as speculation until the cancellation is demonstrated. I would send this to peer review; a good referee will ask for the medium-response check. The paper is honest about its exploratory nature in parts—the conclusion hedges with 'argue'—but the body asserts the cancellation too strongly.","headline":"A clean new jet EEC subtraction observable with a solid pp demonstration, but the heavy-ion medium-response cancellation is asserted, not shown.","tokens_in":11350,"tokens_out":3551,"would_cite":true,"duration_ms":32729,"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 claims that subtracting a 'trivial' energy-energy correlator built from independent single-particle flows from the measured correlator isolates genuine two-particle correlations in jets, and that the same ratio in heavy-ion…","keywords":["energy-energy correlator","jet substructure","particle correlations","jet energy loss","heavy-ion collisions","parton splitting","TMD fragmentation","QCD factorization"],"falsifier":"A heavy-ion Monte Carlo in which the medium response is given an explicit angular distribution (for example, particles added uniformly in annuli of $\\theta$) should leave the double ratio of Eq. (12) unchanged if the cancellation claim is correct; any dependence of that double ratio on the angular distribution of the added response falsifies the claim.","tokens_in":10388,"feed_emoji":"⚛️","tokens_out":8844,"duration_ms":86343,"temperature":0.7,"pith_summary":"The paper argues that the standard energy-energy correlator (EEC) measured inside a jet is not a genuine two-particle correlation: it counts every energy-weighted pair, including pairs of unrelated particles, so it is nonzero even when particles are emitted independently. The authors therefore construct a 'trivial' EEC from two independent single-particle energy flows around the jet axis and compare it with the full EEC, either by subtraction or by ratio. Using Monte Carlo generated jets, they find that the difference and ratio are sizable at both small angles and moderate-to-large angles, and they attribute both to correlated splitting, with non-perturbative fragmentation dominating the smallest angles. If correct, the same comparison becomes a jet-substructure observable that separates hadronization from perturbative splitting and, in heavy-ion collisions, an AA-vs-pp double ratio that exposes medium-modified parton splitting and jet energy loss while cancelling the background from medium response.","feed_headline":"Genuine jet correlations isolated by subtracting trivial pair counts","feed_subtitle":"In heavy-ion collisions, the same ratio exposes jet energy loss and modified parton splitting.","key_machinery":"The machinery is the trivial EEC built from the single-particle energy flows, defined as the angular convolution $\\int \\mathrm{d}^2\\theta_1\\,\\mathrm{d}^2\\theta_2\\, [\\mathrm{d}\\langle E(\\theta_1)\\rangle/\\mathrm{d}^2\\theta_1]\\,[\\mathrm{d}\\langle E(\\theta_2)\\rangle/\\mathrm{d}^2\\theta_2]\\,\\delta^{(2)}(\\vec{\\theta}-(\\vec{\\theta}_1-\\vec{\\theta}_2))$, times a normalization factor $N_{\\rm trivial}\\approx 0.85$ that corrects the normalization to match the full EEC. Equivalently the paper constructs it by 'jet mixing,' assembling fake jets from one particle drawn from many different real jets, which removes all correlations while preserving the single-particle angular and energy-fraction distributions. The full EEC minus this trivial reference, Eq. (9), or divided by it, Eq. (10), is the genuine-correlation observable; because the integral of the difference vanishes by construction, the ratio is used to display the signal in the large-angle region.","core_discovery":"On the paper's own terms, the central discovery is that subtracting the trivial EEC, $\\mathrm{d}\\langle \\mathrm{EEC}(\\theta)\\rangle_{\\mathrm{trivial}}/\\mathrm{d}^2\\theta$, from the measured $\\mathrm{d}\\langle \\mathrm{EEC}(\\theta)\\rangle_{\\mathrm{full}}/\\mathrm{d}^2\\theta$ leaves a nonzero genuine-correlation signal in every angular region, not just at the angles that are usually associated with correlated radiation. The ratio $R_{\\mathrm{EEC}}(\\theta)$ defined in Eq. (10) rises above 1 at small $\\theta$ and again at larger $\\theta$ toward the jet boundary, with a central region where it approaches 1, and the structure matches the 'free hadron', 'transition', and 'collinear' classifications of the jet EEC. The paper interprets the nonzero signal as evidence that the two particles come from a common source, namely a correlated splitting, rather than from two independent energy flows. The paper further claims that in AA collisions the double ratio of Eq. (12) is greater than 1 at small angles because the genuine-correlation ratio is nearly proportional to jet energy, providing a direct handle on the jet energy loss fraction, and that the large-angle behavior exposes medium modification of parton splitting.","pith_inferences":["Inference: the same subtraction could be applied to other jet-substructure distributions, such as angularities or generalized energy correlators, to separate genuine correlations from phase-space and normalization effects, provided a suitable axis and a normalization factor are defined.","Inference: the paper's assumption that the medium response has no angular dependence is testable in heavy-ion Monte Carlo simulations with an explicit medium-response model; if the double ratio changes when the response is angularly modulated, the cancellation premise fails.","Inference: if the near-linearity of $R_{\\mathrm{EEC}}$ with jet energy at small angles is confirmed, the double ratio could be promoted from a qualitative indicator to a quantitative estimator of the fraction of energy lost by the jet, with the uncertainty dominated by the size of the subtraction.","Inference: the claim that two particles at small angle come from a single non-perturbative fragmentation event could be checked by measuring the genuine correlation in electron-positron annihilation, where there is no nuclear medium and hadronization dominates the small-angle region."],"forward_implications":["Measuring $R_{\\mathrm{EEC}}(\\theta)$ in pp collisions gives a direct, model-independent view of genuine two-particle correlations in jets, with the three angular regions mapping to free-hadron emission, the transition region, and collinear parton splitting.","The AA/pp double ratio of Eq. (12) at small angles should exceed 1 and scale with jet energy, allowing the jet energy loss fraction to be read off from the energy dependence.","At moderate/large angles the same double ratio isolates the medium modification of parton splitting, because the trivial background and the medium response cancel.","The method extends to proton-nucleus collisions, where the analogous comparison probes the nuclear modification of EEC observables without single-particle contamination.","It also extends to multi-point energy correlators, offering a family of observables sensitive to higher-order correlations."],"supporting_citations":[{"why":"Original derivation of the EEC from the two-angle correlator, grounding Eq. (4).","marker":"[3]"},{"why":"Provides the collinear factorization and resummation used for the perturbative theta > 0.1 region.","marker":"[13]"},{"why":"Classification of EEC regions into free-hadron, transition, and collinear regimes, used to interpret the ratio structure.","marker":"[22]"},{"why":"Non-perturbative TMD fragmentation mechanism invoked for the small-angle region.","marker":"[40]"},{"why":"Cited for the claim that the medium response has no angular dependence and therefore cancels in the genuine-correlation observables.","marker":"[47]"},{"why":"Supplies the interferometry-style subtraction of uncorrelated pairs that motivates the jet-mixing construction.","marker":"[62]"},{"why":"Supplies the event generator used for the numerical demonstration and figures.","marker":"[63]"},{"why":"TMD fragmentation parameterization for the single energy flow that underpins the small-angle trivial EEC description.","marker":"[70]"}],"fun_headline_variants":["Subtracting trivial pair counts exposes genuine jet correlations","Jets hide genuine correlations that survive trivial subtraction","Genuine correlations in jets appear once trivial pairs are removed","Jet correlations: real signal emerges after removing trivial background","Genuine correlations expose jet energy loss in heavy ions"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The heavy-ion application stands or falls on the assumption that the hot-medium response adds to the EEC with no angular dependence, so that it cancels in the genuine-correlation ratio and double ratio; the paper cites a reference for this but gives no calculation or simulation showing it.","fun_headline_variants_meta":{"raw":{"variants":["Subtracting trivial pair counts exposes genuine jet correlations","Jets hide genuine correlations that survive trivial subtraction","Genuine correlations in jets appear once trivial pairs are removed","Jet correlations: real signal emerges after removing trivial background","Genuine correlations expose jet energy loss in heavy ions"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000742,"raw_usage":{"total_tokens":3286,"prompt_tokens":893,"completion_tokens":2393,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":509,"completion_tokens_details":{"reasoning_tokens":2330}},"tokens_in":509,"tokens_out":2393,"duration_ms":17313,"temperature":1.0,"reasoning_tokens":2330,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-15T18:08:50.970771+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"A heavy-ion Monte Carlo in which the medium response is given an explicit angular distribution (for example, particles added uniformly in annuli of $\\theta$) should leave the double ratio of Eq. (12) unchanged if the cancellation claim is correct; any dependence of that double ratio on the angular distribution of the added response falsifies the claim.","supporting_citations":[{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Original derivation of the EEC from the two-angle correlator, grounding Eq. (4)."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Supplies the interferometry-style subtraction of uncorrelated pairs that motivates the jet-mixing construction."}],"review_version":2}