{"id":"ec2fb9c3-2b29-4b31-ac09-657bd71d1722","arxiv_id":"2501.02794","paper_version":1,"verdict":"CONDITIONAL","confidence":"HIGH","novelty_score":4.0,"correctness_risk":"high","formal_verification":"none","parameter_count":3,"one_line_summary":"AMPT simulations suggest the CME signal-to-background plane ratio b/a is 0.88±0.08 in Au+Au, closer to unity than isobar collisions (0.65±0.18), implying the two-plane CME method is more reliable in Au+Au.","lead":"Using a simulation model of heavy-ion collisions with injected chiral magnetic effect (CME) strength, the authors compare CME-sensitive correlations in gold-gold and isobar collisions at 200 GeV. They conclude the two-plane measurement method is more reliable in gold-gold collisions and that gold-gold may show a stronger CME signal than isobar collisions, especially when measuring relative to the spectator plane.","discovery_kind":"extension","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The claim of stronger CME in Au+Au rests on a chi-square analysis whose participant-plane and spectator-plane fits select incompatible CME strengths (p≈2% vs p≈7.5%); without a combined fit and proper error treatment the conclusion is unsupported.","rationale":"The reader's weakest_assumption focused on the AMPT-model dependence of b as computed by Eq. (13). That is a real concern, since the b/a=0.88 vs 0.65 difference is model-dependent and only marginally significant (about 1.2σ). However, the most load-bearing weakness for the paper's stated conclusion is the internal inconsistency between the participant-plane and spectator-plane chi-square fits. The paper uses the PP fit to claim the data favor small CME signals and the SP fit to claim stronger CME in Au+Au, but these two fits cannot both be valid without a combined treatment. If the PP observable is insensitive to CME, the PP fit says nothing about CME strength; if it is sensitive, then p≈2% and p≈7.5% are contradictory for the same system. The paper does not perform a simultaneous fit, and the chi-square definition in Eq. (14) omits experimental uncertainties, so the quoted best-fit p values are not established with any significance. A concrete combined fit with experimental errors would settle whether the data actually favor a larger CME signal in Au+Au. This is why I recommend keeping the verdict CONDITIONAL rather than accepting the central claim as stated.","tokens_in":20369,"tokens_out":9769,"duration_ms":97951,"concrete_test":"Recompute the Fig. 17 analysis as a simultaneous fit: minimize χ² = Σ_i [ (O_i^PP - E_i^PP)² / (w_i^PP² + σ_i^exp,PP²) + (O_i^SP - E_i^SP)² / (w_i^SP² + σ_i^exp,SP²) ] over a common set (p_Au, p_Ru, p_Zr), using the STAR experimental uncertainties from Refs. [61,76] added in quadrature. Check whether a single p per system can describe both the PP and SP double-ratio observables within errors, and whether the best-fit p_Au is significantly larger than p_Ru and p_Zr. If no common p describes both planes, or if p_Au is not significantly larger, the central claim of stronger CME in Au+Au is unsupported.","verdict_should_be":"CONDITIONAL","load_bearing_attack":"The central claim that Au+Au collisions exhibit a stronger CME signature than isobar collisions is established in the paper through the chi-square analysis shown in Fig. 17 and defined by Eqs. (14)-(15). This analysis is internally inconsistent. For the participant plane (PP), the best fit places all three systems at p≈2% (panels a and c). For the spectator plane (SP), the best fit places Au+Au at p=7.5-10% and the isobars at p=5-7.5% (panels b and d). The paper interprets this as the SP being more sensitive to CME, but that interpretation is not logically available: if the PP observable is insensitive to CME, then the PP fit cannot constrain p and cannot be cited as evidence for small CME signals; if it is sensitive, then the two planes give contradictory CME strengths for the same collision system. Either way, the data do not currently establish that Au+Au has a stronger CME. The statistical basis is additionally fragile because Eq. (14) uses only the model error w_o and omits experimental uncertainties, and the p grid is coarse (0, 2, 5, 7.5, 10%), so the reported differences in best-fit p values (e.g., 7.5% vs 5%, or 10% vs 7.5%) are not shown to be significant. The b/a=0.88 result is a legitimate model output, but the abstract's 'stronger CME signature in Au+Au' conclusion depends on this chi-square analysis, making the inconsistency load-bearing.","agreement_with_reader":"partial"},"referee_report":{"model":"deepseek-v4-flash","summary":"The manuscript extends the authors' previous AMPT-based two-plane study of the chiral magnetic effect (CME) from isobar collisions to Au+Au collisions at sqrt(s_NN)=200 GeV. It implements a CME-like charge separation with tunable strength p, reconstructs spectator and participant planes, and computes the ratio b = Delta-gamma_CME{PP}/Delta-gamma_CME{SP} through Eq. (13). The authors report b/a = 0.88 +/- 0.08 for Au+Au, compare it with their earlier isobar value 0.65 +/- 0.18, and perform a chi-square scan over p for Au+Au, Ru+Ru, and Zr+Zr using the double ratio Delta-gamma/(v2 dNch/deta). On this basis they claim that the two-plane method is less biased in Au+Au collisions and that Au+Au exhibits a stronger CME signal, especially with respect to the spectator plane.","tokens_in":20743,"tokens_out":6670,"duration_ms":61930,"significance":"The algebraic derivation of fCME{b} in Eq. (12) is correct, and the systematic use of AMPT to track a and b through the evolution stages is informative; the paper offers a falsifiable, quantitative framework for interpreting two-plane measurements. If the claimed b/a contrast and the chi-square hierarchy were statistically robust, the result would be valuable for planning Au+Au measurements. However, the central cross-system conclusion currently rests on a marginally significant b/a difference and on chi-square fits that use only model errors and a coarse p grid; the internal inconsistency between participant-plane and spectator-plane fits prevents the data from establishing the stronger-CME claim. The paper is a useful model study, but its headline conclusion is not yet supported at the claimed level.","major_comments":[{"comment":"The headline comparison b/a(Au+Au) = 0.88 +/- 0.08 versus b/a(isobar) = 0.65 +/- 0.18 is not statistically significant: the difference is roughly 0.23 while the quadrature-summed uncertainty is about 0.20, corresponding to about 1.2 sigma. Statements in the abstract and in Sec. IV that Au+Au shows a 'reduced difference' and 'enhances the experimental reliability' therefore go beyond what the two model outputs establish. Please provide a proper propagation of the two determinations, or soften the claim to a suggestive trend.","section":"Sec. III, Fig. 11 and Sec. IV"},{"comment":"The chi-square definition in Eq. (14) uses only the model error w_o in the denominator and omits the experimental uncertainties on E_i, and the p grid is coarse (0, 2, 5, 7.5, 10%) with no confidence intervals or Delta-chi^2 thresholds. The reported differences between best-fit p values, for example Au+Au at 7.5% versus Ru+Ru at 5% and Au+Au at 10% versus Zr+Zr at 7.5%, are therefore not shown to be significant. A combined fit that includes experimental errors and reports Delta-chi^2 contours is needed before these values can support the claim of stronger CME in Au+Au.","section":"Sec. III, Eqs. (14)-(15) and Fig. 17"},{"comment":"The participant-plane fits select p about 2% for all three systems, while the spectator-plane fits select p = 7.5-10% for Au+Au and p = 5-7.5% for the isobars. The text interprets this as greater SP sensitivity, but no combined fit is performed. If the PP observable is insensitive to the CME, the PP fit cannot constrain p and cannot be used to argue that the CME is small; if it is sensitive, the two planes give mutually inconsistent CME strengths for the same systems. Either way, the present analysis does not establish that Au+Au has a stronger CME signal.","section":"Sec. III, Fig. 17 panels (a)-(d)"},{"comment":"The value b/a = 0.88 +/- 0.08 is an internal AMPT output, computed from the same model used to generate the CME signal, and the extraction procedure is underspecified: the text does not state which p values, centrality bins, and error treatment enter the constant-fit value, and the p = 2% point is excluded 'due to its large statistical uncertainties' without a documented criterion. Because the claimed Au+Au advantage is driven by the stage-dependent decrease of b/a in Figs. 15-16, the model uncertainty on b/a (for example, from parton cross-section or string-melting parameters) should be quantified for the conclusion to be robust.","section":"Sec. II C, Eqs. (12)-(13) and Figs. 9-11"}],"minor_comments":[{"comment":"The sum is written as 'nX k=0' and the indices k and n are inconsistent; please define all indices and clarify what 'normalized chi-square' means.","section":"Eq. (14)"},{"comment":"The quantity fCME{p} is plotted but never defined in the text; please add its definition or cite the precise equation from Ref. [64].","section":"Fig. 14"},{"comment":"The notation <...> is used both for event averages in Eqs. (2)-(3) and in the double-average notation of Eqs. (4)-(5); please define the averaging convention explicitly.","section":"Eqs. (2)-(5)"},{"comment":"There are several typographical issues, including the stray Chinese comma after 'AMPT model ，' in the introduction and inconsistent comma usage in the Fig. 6 caption.","section":"Introduction and Fig. 6 caption"},{"comment":"Ref. [57] is an arXiv preprint from 2024; please update it if a published version now exists.","section":"References"}],"recommendation":"major_revision","confidential_remarks":"The paper fits the scope of the journal and the model study is competent. My main concern is that the abstract and summary overstate the strength of the evidence: the b/a difference between systems is not significant, and the chi-square analysis is internally inconsistent between the participant and spectator planes. I would encourage the editor to request the statistical reanalysis described in the major comments; with those changes the paper could become publishable."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"The new thing here is an AMPT-based estimate of b/a for Au+Au collisions, 0.88 ± 0.08, using the same two-plane framework as the authors' earlier isobar study, plus a first attempt at a simultaneous three-system comparison against STAR data. The derivation of the corrected fCME{b} formula is clean, and the stage-evolution plots—showing b decreasing through the parton cascade and hadronic rescatterings—are physically sensible and useful. That part is worth reading.\n\nThe soft spot is the headline conclusion. The chi-square fits in Fig. 17 put all three systems near p≈2% when using the participant plane, but put Au+Au at 7.5–10% and the isobars at 5–7.5% when using the spectator plane. The paper interprets this as the SP being more sensitive, but that reading is not logically available: if the PP observable is insensitive to CME, then the PP fit cannot constrain p and cannot be cited as evidence for small CME; if it is sensitive, then the two planes give contradictory CME strengths for the same system. Either way, the data do not establish a stronger CME in Au+Au. The statistical basis is also thin: Eq. (14) uses only the model error, omitting experimental uncertainties, and the p grid (0, 2, 5, 7.5, 10%) is too coarse to resolve differences like 7.5% vs 5%.\n\nThe b/a difference between Au+Au and isobar is about 1.2σ when errors are combined (0.88 ± 0.08 vs 0.65 ± 0.18), so the phrase \"reduced difference\" is overstated. And b itself is computed from the same AMPT model that provides the simulated CME signal, with no external validation and no code or data release. That doesn't invalidate the model study, but it means the central claim is a model-dependent translation, not an independent finding.\n\nMy take: the b/a=0.88 result and the stage-evolution mechanism are worth publishing, but the \"stronger CME in Au+Au\" conclusion should be removed or reworked. The paper deserves peer review because a good referee can push for a combined fit with proper error propagation and a clearer statement of what the PP fits can and cannot constrain. I would not cite the central claim in its current form, but I might cite the b/a value as a model prediction.\n\nRecommendation: send it to review, but expect the conclusion to be substantially softened in revision.","headline":"The b/a=0.88 result for Au+Au is a credible model output, but the paper's central claim of a stronger CME in Au+Au rests on a chi-square analysis that is internally inconsistent across the two planes and statistically fragile.","tokens_in":21281,"tokens_out":2149,"would_cite":true,"duration_ms":21502,"reading_group":"maybe","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":[],"model":"deepseek-v4-flash","headline":"The paper claims that the two-plane CME extraction is more reliable in Au+Au than in isobar collisions, with $b/a = 0.88 \\pm 0.08$, and that Au+Au shows a stronger CME signal when the spectator plane is used.","keywords":["chiral magnetic effect","two-plane method","spectator plane","participant plane","charge-dependent azimuthal correlations","AMPT model","isobar collisions","Au+Au collisions"],"falsifier":"In STAR data for 20–50% centrality, the spectator-plane double ratio $(\\Delta\\gamma/v_2)\\,dN_{\\rm ch}/d\\eta$ should order Au+Au > Ru+Ru > Zr+Zr if the paper's chi-square conclusion is right; a measurement with small enough errors that breaks this ordering would falsify the claim of a stronger CME in Au+Au.","tokens_in":20158,"feed_emoji":"🧲","tokens_out":15668,"duration_ms":111372,"temperature":0.7,"pith_summary":"The paper tries to establish where the chiral magnetic effect (CME) shows up most cleanly in relativistic heavy-ion collisions at 200 GeV, by comparing Au+Au collisions with the isobar systems Ru+Ru and Zr+Zr. It uses the two-plane method: the charge-separation observable $\\Delta\\gamma$ is measured relative to the participant plane (the overlap zone of the collision) and to the spectator plane (non-interacting nucleons, which track the magnetic field better). The central quantitative result is that the CME signal-to-background ratio between the two planes, $b/a$, is $0.88 \\pm 0.08$ for Au+Au, much closer to unity than the isobar value $0.65 \\pm 0.18$; because the standard extraction formula assumes $b/a=1$, a value closer to 1 means the method is less biased. A chi-square fit of the transport model to STAR data then indicates that Au+Au carries a stronger CME signal than Ru+Ru or Zr+Zr, especially when the spectator plane is used. If correct, future CME searches should favor Au+Au over isobar systems and treat the spectator-plane $\\Delta\\gamma$ as the more sensitive observable.","feed_headline":"b/a = 0.88 makes Au+Au the more reliable CME probe","feed_subtitle":"The two-plane method's key assumption holds better in Au+Au than in isobars, making its CME extraction more reliable.","key_machinery":"The machinery is the two-plane decomposition of the charge-dependent azimuthal correlator $\\Delta\\gamma\\{\\psi\\} = \\Delta\\gamma_{\\rm Bkg}\\{\\psi\\} + \\Delta\\gamma_{\\rm CME}\\{\\psi\\}$, where $\\psi$ is either the spectator plane $\\psi_{\\rm SP}$ or the participant plane $\\psi_{\\rm PP}$. The ratios $a = v_2\\{SP\\}/v_2\\{PP\\}$ and $A = \\Delta\\gamma\\{SP\\}/\\Delta\\gamma\\{PP\\}$ enter the standard extraction formula $f_{\\rm CME} = (A/a - 1)/(1/a^2 - 1)$, which assumes the CME signal ratio is the same as the flow ratio; the paper replaces this with $b = \\Delta\\gamma_{\\rm CME}\\{PP\\}/\\Delta\\gamma_{\\rm CME}\\{SP\\}$, obtained from Eq. (13) as the difference between CME-on and CME-off AMPT simulations. The key mechanism is that final-state rescattering rotates and damps the CME current, decorrelating it from the participant plane while the spectator plane keeps tracking the magnetic field direction; this decorrelation is weaker in Au+Au than in Ru+Ru, which is why $b/a$ stays closer to 1 in Au+Au.","core_discovery":"The paper's central claim is that the ratio $b = \\Delta\\gamma_{\\rm CME}\\{PP\\}/\\Delta\\gamma_{\\rm CME}\\{SP\\}$, computed in the AMPT model by subtracting the no-CME ($p=0$) simulation from the CME-on ($p>0$) simulation via Eq. (13), is not equal to $a = v_2\\{SP\\}/v_2\\{PP\\}$, and that the discrepancy is smaller in Au+Au than in isobar collisions. In 20–50% centrality Au+Au collisions the paper finds $b/a = 0.88 \\pm 0.08$, whereas its earlier isobar study found $0.65 \\pm 0.18$. Because the modified two-plane formula $f_{\\rm CME} = (A/a - 1)/(1/ab - 1)$ reduces to the standard formula only when $b=a$, the Au+Au value shows the correction is mild there. Stage-by-stage evolution in the AMPT model shows $b$ falling as final-state interactions decorrelate the CME current from the participant plane, but less steeply in Au+Au than in Ru+Ru. A simultaneous chi-square fit to STAR data for the three systems prefers a CME strength near 2% when the participant plane is used, but 7.5–10% for Au+Au (5–7.5% for isobars) when the spectator plane is used, which the authors read as a stronger CME signature in Au+Au.","pith_inferences":["If the trend $b/a \\to 1$ with increasing system size is real, then the two-plane method should be even more reliable in larger collision systems such as U+U or Pb+Pb, and less reliable in smaller systems; this extrapolation is not made in the paper.","The gap between the participant-plane fit ($p \\approx 2\\%$) and the spectator-plane fit ($p \\approx 7.5$–$10\\%$) suggests the CME signal may be partly hidden in the participant-plane view; a measurement constraining both planes with better non-flow control would decide which plane carries the truth.","A natural independent test would be to compute $b$ in a different framework, such as anomalous hydrodynamics with a time-dependent magnetic field; agreement with $b/a=0.88$ for Au+Au and $0.65$ for isobars would confirm that the AMPT decorrelation mechanism is the right physics.","Because the paper uses the initial-state spectator plane as a proxy for the magnetic field direction, a direct reconstruction of the field direction (or a calculation with a fully dynamical field) could either strengthen or weaken the claimed spectator-plane advantage."],"forward_implications":["Two-plane extractions of the CME fraction should quote $f_{\\rm CME}\\{b\\}$ using a transport-model value of $b$, rather than assuming $b=a$; in Au+Au the correction is mild, so the standard formula is a better approximation there than in isobars.","The spectator-plane $\\Delta\\gamma$ is the observable to focus on: the model fits require a CME strength of 7.5–10% in Au+Au versus about 2% for the participant plane, so a positive CME signal of that size should be visible in STAR data.","The stage-by-stage decrease of $b/a$ in the AMPT model means the two-plane method's reliability is system-size dependent, not a fixed property of the observable.","If Au+Au indeed has a stronger CME signature than Ru+Ru and Zr+Zr, then the isobar upper limits do not directly constrain the CME in Au+Au.","The double-ratio $\\Delta\\gamma/v_2 \\, dN_{\\rm ch}/d\\eta$ with respect to the spectator plane is the discriminator that separates Au+Au from the isobar systems in the chi-square analysis."],"supporting_citations":[{"why":"Previous AMPT two-plane study of Ru+Ru and Zr+Zr giving $b/a = 0.65 \\pm 0.18$; supplies the isobar baseline and the method for computing $b$.","marker":"[64]"},{"why":"Proposes the spectator-plane/participant-plane two-plane method for CME detection.","marker":"[58]"},{"why":"Introduces the two-plane $\\Delta\\gamma$ formalism and the relation $a = \\langle \\cos 2(\\psi_{PP}-\\psi_{SP}) \\rangle$.","marker":"[59]"},{"why":"STAR two-plane Au+Au and isobar data used for the comparisons and chi-square fits.","marker":"[61]"},{"why":"STAR isobar results for CME fractions, averaged and compared in the ratio analysis.","marker":"[76]"},{"why":"AMPT implementation of initial CME-like charge separation and demonstration that final-state interactions damp it; basis of Eq. (13).","marker":"[75]"},{"why":"Shows non-flow effects in event-plane reconstruction and motivates the need for the $b$ correction.","marker":"[62]"},{"why":"Critically notes that the CME ratio $b$ may differ from the flow ratio $a$, motivating the modified formula.","marker":"[63]"},{"why":"The AMPT multiphase transport model in which all simulations in the paper are performed.","marker":"[65]"},{"why":"Shows that final-state interactions rotate the CME current direction in the anisotropic overlap zone, the decorrelation mechanism behind the $b/a$ decrease.","marker":"[52]"}],"fun_headline_variants":["b/a=0.88 in Au+Au: two-plane method holds","Au+Au: b/a=0.88, so two-plane method reliable","b/a discrepancy smaller in Au+Au, so CME probe is robust","Au+Au yields b/a≈1, making CME extraction reliable"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The central conclusion depends on the AMPT model correctly capturing how final-state rescattering rotates and damps the chiral-magnetic-effect current relative to the participant plane; if that decorrelation is unrealistic, the $b/a = 0.88$ value and the Au+Au advantage would not transfer to experiment.","fun_headline_variants_meta":{"raw":{"variants":["b/a=0.88 in Au+Au: two-plane method holds","Au+Au: b/a=0.88, so two-plane method reliable","b/a discrepancy smaller in Au+Au, so CME probe is robust","Au+Au yields b/a≈1, making CME extraction reliable"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000783,"raw_usage":{"total_tokens":3507,"prompt_tokens":1046,"completion_tokens":2461,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":662,"completion_tokens_details":{"reasoning_tokens":2378}},"tokens_in":662,"tokens_out":2461,"duration_ms":17687,"temperature":1.0,"reasoning_tokens":2378,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-10T22:04:05.479271+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"In STAR data for 20–50% centrality, the spectator-plane double ratio $(\\Delta\\gamma/v_2)\\,dN_{\\rm ch}/d\\eta$ should order Au+Au > Ru+Ru > Zr+Zr if the paper's chi-square conclusion is right; a measurement with small enough errors that breaks this ordering would falsify the claim of a stronger CME in Au+Au.","supporting_citations":[],"review_version":1}