{"id":"8ba912c6-daec-4116-943d-d6f1e0fccbaa","arxiv_id":"2506.19033","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":5.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":1,"one_line_summary":"In the AMPT model, the medium-induced enhancement of the groomed jet mass at high Mg/pT in PbPb collisions comes from large-angle elastic scattering during the parton cascade, not from hadronization.","lead":"Using the AMPT transport model, this paper computes jet grooming observables in proton-proton and lead-lead collisions at 5.02 TeV and finds that the groomed jet mass grows at high values in central events because of elastic jet-medium interactions at large angles. The same model reproduces CMS baseline data, which makes the comparison useful for interpreting jet quenching measurements.","discovery_kind":"extension","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The large-angle conclusion is confounded: the two Soft Drop settings differ in both z_cut and beta, so the null result under strong grooming does not isolate angular dependence.","rationale":"The reader's weakest assumption focuses on the absence of radiative/inelastic energy loss in AMPT's ZPC parton cascade. That is a real limitation, and the authors explicitly acknowledge it in Sec. IV when they say incorporating radiative losses is expected to add more small-angle splittings. However, the paper is framed as an AMPT model study, so the elastic-only nature of the cascade does not by itself invalidate the internal comparison between 3 mb and 0 mb runs; it mainly limits extrapolation to full QCD. The more directly load-bearing gap is the inference from the two grooming settings to 'large-angle scattering.' Because Eq. (3) couples z_cut and beta, the difference between (0.1,0.0) and (0.5,1.5) cannot be attributed uniquely to the angular suppression. The 'no significant changes' under strong grooming is a null result that is equally consistent with the modification being carried by asymmetric splittings with moderate angles, which the higher z_cut removes. This concern targets the paper's headline physics conclusion rather than just its model completeness. I also credit the paper for the pp baseline agreement with CMS data in Figs. 2 and 4 and for the staged-evolution control in Fig. 7, which genuinely supports the claim that the enhancement appears during the parton cascade rather than in later stages. The recommendation remains CONDITIONAL, as the reader originally concluded, because the enhancement and its parton-cascade origin are plausible but the large-angle interpretation needs either a direct phase-space decomposition or control grooming settings to be established.","tokens_in":15967,"tokens_out":14067,"duration_ms":160365,"concrete_test":"Recompute the PbPb/smeared-pp Mg/pT,jet ratio in the same 0-10% centrality and 160<pT,jet<180 GeV bin as Fig. 5 for two additional Soft Drop settings: (z_cut=0.1, beta=1.5) and (z_cut=0.5, beta=0.0). If the enhancement survives at (0.1,1.5) or disappears at (0.5,0.0), the large-angle attribution is unsupported; if it follows the angular factor rather than the z_cut threshold, the conclusion is corroborated. Also add bootstrap or run-to-run uncertainties to the ratio curves.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The abstract and Sec. III B conclude that the Mg/pT,jet enhancement is 'predominantly associated with large-angle scattering' solely from the contrast between the (z_cut=0.1, beta=0.0) and (z_cut=0.5, beta=1.5) settings. These settings change two parameters at once in Eq. (3): raising z_cut from 0.1 to 0.5 excludes all but nearly symmetric splittings, while increasing beta from 0 to 1.5 additionally suppresses large-angle splittings. A vanishing modification under the second setting therefore does not identify the angular factor as the cause; it is equally consistent with the enhancement living in asymmetric splittings with moderate angles and z_g just above 0.1, which the z_cut=0.5 condition removes. Fig. 1 documents where the two groomings operate in the Lund plane but not where the medium modification resides. The claim is not rescued by the stage analysis, which only establishes that the modification appears during the parton cascade. The elastic-only limitation acknowledged in Sec. IV qualifies the QCD extrapolation, but the confounded grooming comparison is a more immediate internal gap. Additionally, Sec. III B itself calls the z_cut=0.1 effect 'a hint' while the abstract says 'pronounced,' and the model curves carry no statistical uncertainties, so the positive evidence is not quantitatively secured.","agreement_with_reader":"partial"},"referee_report":{"model":"deepseek-v4-flash","summary":"This manuscript presents an AMPT (string melting) study of the Soft Drop groomed observables z_g and M_g/pT_jet in pp and PbPb collisions at sqrt(s_NN) = 5.02 TeV, using constituent subtraction to mitigate background and the CMS-like smearing procedure for pp comparisons. The authors report a slight enhancement of asymmetric z_g splittings in central PbPb events, a pronounced enhancement of the high-M_g/pT_jet tail at low pT_jet and in central events, and a stage-by-stage analysis indicating that this enhancement appears during the parton cascade and is largely preserved through hadronization and hadronic rescatterings. They further find that a stronger grooming setting (z_cut=0.5, beta=1.5) removes the M_g/pT_jet modification, and interpret this as evidence that the medium-induced modification is predominantly associated with large-angle scattering. The paper compares the model with CMS data in pp and PbPb and reports qualitative agreement, with the 0 mb parton-cross-section setting serving as a no-interaction baseline.","tokens_in":16212,"tokens_out":3216,"duration_ms":38038,"significance":"If the conclusions are supported, the paper offers a controlled and parameter-free-with-respect-to-the-target-observables model study of jet-medium interactions, with a clean 3 mb versus 0 mb comparison and a dynamical-stage decomposition. The strengths are that the parton cross section (3 mb) is fixed by earlier flow studies rather than fitted to the substructure data, and that the four-stage analysis in Fig. 7 is a useful diagnostic for separating partonic and hadronic effects. The comparison with CMS data for both z_g and M_g/pT_jet also anchors the model. However, the central attribution of the effect to large-angle scattering is not uniquely determined by the presented grooming comparison, and the quantitative significance of the enhancement is not established because the model curves carry no statistical uncertainties. These points are load-bearing for the abstract's claims, so the current version is not yet ready for acceptance.","major_comments":[{"comment":"All model curves are shown without statistical uncertainties, although the central positive claim is a 'pronounced enhancement' in the high-M_g/pT_jet region. Without uncertainties on the ratios, a reader cannot judge whether the enhancement in the last bin of Fig. 5 (left) or the low-pT_jet enhancement in Fig. 6 (left) is statistically significant or a fluctuation. The manuscript itself calls the effect 'a hint' in Sec. III B while the abstract calls it 'pronounced'; this inconsistency underscores the need for uncertainty quantification. The authors should either include statistical error bands on the AMPT ratios or explicitly report the statistical significance of the enhancement bins.","section":"III B, Figs. 4–7"},{"comment":"The AMPT parton cascade used here contains only two-body elastic scatterings; there are no radiative or inelastic energy-loss processes in the model. Since the claimed enhancement is traced entirely to the parton cascade stage, the conclusion that 'jet-medium interactions' produce the enhancement is a statement about elastic scattering only. The manuscript acknowledges this in Sec. IV, but the abstract and Sec. III B state the large-angle conclusion without this qualification. The wording should be changed to make explicit that the model predicts that elastic scattering produces the effect, and that a radiative-energy-loss implementation may alter the small-angle behavior, which is already noted in the final paragraph. This is a scope limitation rather than an internal inconsistency, but it is essential to the interpretation of the central claim.","section":"II A (2), IV"}],"minor_comments":[{"comment":"The terminology is inconsistent: the abstract says a 'pronounced enhancement' while Sec. III B (after Fig. 5) calls the same effect 'a hint of enhancement'; the authors should use one consistent descriptor once statistical significance is quantified.","section":"Abstract and III B"},{"comment":"The sentence 'In a word, our analysis demonstrates...' is informal for a journal article; 'In summary' would be more suitable.","section":"III B"},{"comment":"The captions list centrality and pT_jet offset labels, but the figures themselves do not define the offset constants; a brief explanation of the '(+N)' notation in the caption would improve readability.","section":"Fig. 5 and Fig. 6 captions"},{"comment":"The definition of M_g via the two Soft Drop subjets is correct for the working point used, but a sentence clarifying that the groomed jet mass is computed from the two subjets, rather than from all groomed constituents, would remove a possible ambiguity for readers familiar with other Soft Drop implementations.","section":"II C, Eq. (5)"},{"comment":"In the discussion of JEWEL, the phrase 'with four-momentum subtraction method' could be expanded to 'with the four-momentum subtraction scheme for medium response' to be more precise, though the reference is clear.","section":"III A"}],"recommendation":"major_revision","confidential_remarks":"The paper is within the journal's scope and uses a well-established model. The lack of uncertainties and the two-parameter confounding are the main technical obstacles; both are addressable with additional runs and revised wording, so rejection is not warranted. I would encourage the editor to request a revision that either adds a beta-scan or a z_cut-scan at fixed beta, and that either adds statistical error bands or quantifies the significance of the enhancement bins. The self-citation of Ref. [61] is appropriate and does not appear to mask a conflict."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Plain take: this is a legitimate, well-scoped AMPT study that deserves a serious referee, but the headline conclusion — that the M_g/pT enhancement is 'predominantly associated with large-angle scattering' — outruns the evidence in the paper.\n\nThe genuinely useful parts: the authors extend their earlier ungroomed jet mass work [61] to groomed z_g and M_g/pT, and add a four-stage decomposition of the modification. The controlled 3 mb vs 0 mb comparison plus the stage analysis credibly shows that the high-M_g/pT tail appears during the parton cascade and that grooming suppresses the hadronization and hadronic-rescattering contributions. The pp baseline agrees with CMS; no parameter is fitted to the target observables (the 3 mb cross section is from flow calibration, the Soft Drop settings from CMS). That is honest, reproducible modeling, and the self-citation to [61] is contextual, not self-serving.\n\nWhere it gets soft, in order of importance:\n\n1. The large-angle claim is confounded. The two grooming settings differ in both z_cut (0.1 vs 0.5) and beta (0 vs 1.5). Since z_cut=0.5 removes all but nearly symmetric splittings, the null under the stronger grooming is equally consistent with the enhancement living in asymmetric splittings at moderate angles. Fig. 1 shows where each grooming operates, not where the medium modification lives, and the stage analysis only localizes the effect to the parton cascade. An intermediate setting (e.g., z_cut=0.5, beta=0) is needed to separate the two parameters. This is an internal gap in the argument, distinct from the acknowledged elastic-only limitation of the ZPC cascade.\n\n2. The evidence strength is described inconsistently: the abstract says 'pronounced enhancement' while Sec. III B calls it 'a hint.' The model curves carry no uncertainties, so the significance of the tail enhancement cannot be assessed by the reader.\n\n3. The elastic-only parton cascade is acknowledged in Sec. IV, rightly, but it should be stated earlier and more prominently, since the physical reading of 'jet-medium interactions' rests on a model without radiative energy loss.\n\nMinor: no code or data release; the comparison to CMS is qualitative but reasonable given the smeared-pp procedure.\n\nThe central result — the enhancement originates in the elastic parton cascade and grooming suppresses non-perturbative contributions — holds up within the model. The angular attribution needs to be softened or re-derived with a better-controlled comparison. I'd send it to peer review with a request for that, plus uncertainties and a consistent description of the effect's size. Worth a reading group slot mainly to argue about the Lund-plane logic.","headline":"Useful AMPT stage-decomposition study of groomed jet mass, but the headline 'large-angle scattering' claim is confounded: the two Soft Drop settings change both z_cut and beta, so the null under strong grooming does not isolate angular dependence.","tokens_in":16753,"tokens_out":4607,"would_cite":true,"duration_ms":42825,"reading_group":"maybe","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":"This paper shows that the enhancement of groomed jet mass in central lead-lead collisions originates from elastic jet-medium scattering at large angles, not from hadronization or hadronic rescatterings.","keywords":["jet substructure","groomed jet mass","soft drop grooming","jet-medium interactions","AMPT model","parton cascade","heavy-ion collisions","large-angle scattering"],"falsifier":"Run the same AMPT setup with radiative energy loss added while leaving elastic scatterings unchanged: if the high-mass tail in $M_g/p_{T,\\mathrm{jet}}$ disappears rather than persisting, the claim that elastic large-angle scattering is the dominant mechanism is falsified.","tokens_in":15752,"feed_emoji":"⚛️","tokens_out":12112,"duration_ms":96864,"temperature":0.7,"pith_summary":"This paper argues that the enhancement of the groomed jet mass over jet transverse momentum ($M_g/p_{T,\\mathrm{jet}}$) seen in central lead-lead collisions at 5.02 TeV is produced by elastic jet-medium interactions in the partonic phase, and that these interactions act predominantly at large angles from the jet axis. The claim is established by comparing transport-model simulations with and without partonic scatterings, and by turning the Soft Drop grooming handles: a weak grooming setting ($z_{\\mathrm{cut}}=0.1,\\beta=0.0$) preserves the enhancement, while a strong setting ($z_{\\mathrm{cut}}=0.5,\\beta=1.5$) removes it. The paper therefore identifies soft-drop groomed jet mass as a practical observable for isolating large-angle elastic energy transport in the quark-gluon plasma.","feed_headline":"Groomed jet mass reveals large-angle scattering in heavy-ion jets","feed_subtitle":"In central PbPb collisions, the high-mass tail comes from elastic parton scatterings, not hadronization.","key_machinery":"The load-bearing mechanism is the Soft Drop grooming algorithm applied with two parameter sets, operating on jets reconstructed with the anti-$k_T$ algorithm ($R=0.4$) after constituent subtraction. The weak setting ($z_{\\mathrm{cut}}=0.1,\\beta=0.0$) keeps peripheral subjets, exposing the large-angle medium response; the strong setting ($z_{\\mathrm{cut}}=0.5,\\beta=1.5$) restricts the groomed jet to its core, hiding that response. The argument also relies on the stage-by-stage decomposition of the AMPT model (initial state, parton cascade, hadronization, hadronic rescatterings), which isolates the parton-cascade contribution from non-perturbative late-stage effects.","core_discovery":"In central PbPb collisions at $\\sqrt{s_{NN}}=5.02$ TeV, the Soft Drop groomed jet mass ratio $M_g/p_{T,\\mathrm{jet}}$ develops a pronounced high-mass tail that grows as events become more central and as $p_{T,\\mathrm{jet}}$ decreases, while the splitting fraction $z_g$ shows only a slight shift toward asymmetric splittings. Tracing the observable stage by stage through the AMPT multi-phase transport model evolution, the entire enhancement appears at the parton-cascade stage, where the jet's partons undergo two-body elastic scatterings with medium partons; hadronization and hadronic rescatterings add negligible contribution after grooming. Switching off partonic interactions (0 mb cross section) removes the modification entirely, and applying a stronger grooming condition that suppresses large-angle subjets also removes it, indicating that the modification is carried by large-angle scattering.","pith_inferences":["One extension not drawn out in the paper would be to correlate the size of the high-mass tail with the jet path length through the medium; a centrality-selected measurement at fixed $p_{T,\\mathrm{jet}}$ could test that dependence directly.","Applying the same stage-decomposition to the groomed splitting radius $r_g$ would likely show almost no medium modification, since small-angle splittings are dominated by vacuum radiation.","If radiative energy loss were added to the cascade, the generated small-angle splittings might dilute the large-angle high-mass tail; the paper itself flags radiative loss as a future direction."],"forward_implications":["If the claim holds, $M_g/p_{T,\\mathrm{jet}}$ can serve as a targeted probe of large-angle elastic energy transport in the quark-gluon plasma, complementing $z_g$ and $r_g$.","The enhancement is largest in 0-10% central events and at $p_{T,\\mathrm{jet}}<160$ GeV, giving a concrete scaling benchmark for models that include medium response.","The absence of modification under strong grooming implies that the jet core remains essentially unmodified, so the medium acts primarily on the periphery of the jet.","Because the enhancement appears entirely at the parton-cascade stage in this model, late-stage hadronic interactions cannot be its source."],"supporting_citations":[{"why":"Defines the AMPT multi-phase transport model used for the entire simulation and stage decomposition.","marker":"[62]"},{"why":"Implements the two-body elastic parton cascade that the paper identifies as the origin of the enhancement.","marker":"[71]"},{"why":"Provides the Soft Drop grooming algorithm whose parameter settings expose or suppress the large-angle effect.","marker":"[96]"},{"why":"Gives the constituent subtraction method used to remove the heavy-ion background from jet observables.","marker":"[93]"},{"why":"Supplies the measured $z_g$ distribution used as the baseline for the splitting-fraction comparison.","marker":"[46]"},{"why":"Supplies the measured $M_g/p_{T,\\mathrm{jet}}$ distribution that the paper compares against.","marker":"[50]"},{"why":"Earlier AMPT study emphasizing elastic energy transport from the jet core to large angles.","marker":"[87]"},{"why":"Earlier AMPT study supporting the same large-angle elastic transport mechanism.","marker":"[88]"}],"fun_headline_variants":["Large-angle scattering drives jet mass tail in PbPb","Groomed jet mass pinpoints large-angle scattering in heavy-ion jets","Central PbPb jets show mass tail from partonic elastic scatterings","Jet mass probe isolates large-angle scattering in heavy-ion collisions","Groomed jet mass tail in PbPb traced to large-angle parton scattering"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The load-bearing assumption is that the AMPT parton cascade, which contains only two-body elastic scatterings and no radiative energy loss, captures the dominant jet-medium interactions behind the mass enhancement; if inelastic processes such as medium-induced gluon radiation are required to produce the tail, the paper's large-angle elastic interpretation is weakened.","fun_headline_variants_meta":{"raw":{"variants":["Large-angle scattering drives jet mass tail in PbPb","Groomed jet mass pinpoints large-angle scattering in heavy-ion jets","Central PbPb jets show mass tail from partonic elastic scatterings","Jet mass probe isolates large-angle scattering in heavy-ion collisions","Groomed jet mass tail in PbPb traced to large-angle parton scattering"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000663,"raw_usage":{"total_tokens":3055,"prompt_tokens":1000,"completion_tokens":2055,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":616,"completion_tokens_details":{"reasoning_tokens":1965}},"tokens_in":616,"tokens_out":2055,"duration_ms":13979,"temperature":1.0,"reasoning_tokens":1965,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-15T18:38:37.929683+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Run the same AMPT setup with radiative energy loss added while leaving elastic scatterings unchanged: if the high-mass tail in $M_g/p_{T,\\mathrm{jet}}$ disappears rather than persisting, the claim that elastic large-angle scattering is the dominant mechanism is falsified.","supporting_citations":[],"review_version":2}