{"id":"572ac395-6daa-43fb-9a03-9bfd454e476d","arxiv_id":"2608.10496","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":4.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":5,"one_line_summary":"An event-by-event CME source in an improved AMPT model predicts a surviving charge-separation signal in p+A collisions, strongest for the IV minus II geometry difference.","lead":"This paper uses a modified AMPT transport model to simulate chiral magnetic effect (CME) charge separation in polarized proton-gold collisions. It reports that a new geometric difference observable survives hadronic evolution and could isolate CME from ordinary background.","discovery_kind":"extension","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The 7% CME ceiling in Eq. (6) is calibrated to the background-dominated Au+Au γSS; if the isobar-constrained CME fraction is lower, the predicted ΔγIV − ΔγII of 1–2×10^-4 scales down and may fall below detectability.","rationale":"The reader's weakest_assumption identifies the 7% calibration in Eq. (6) as the most load-bearing risk. I agree: the calibration observable γSS in Au+Au is explicitly background-dominated (Sec. I, [25]), so deriving a CME source strength from it is circular unless the model's own background is shown to be negligible. The paper provides no such check. The central claim's quantitative part, the 1–2 × 10^-4 difference, is proportional to this ceiling, and the isobar constraint suggests the true CME fraction could be far below 7%, potentially reducing the signal to an unobservable level. The qualitative hierarchy and the background-cancelling nature of the inter-scheme difference would survive, but the paper's headline prediction would not. I therefore find no reason to change the reader's CONDITIONAL verdict: the concept is plausible, but the normalization needs independent validation. No new concern beyond the reader's is identified.","tokens_in":10995,"tokens_out":9378,"duration_ms":81919,"concrete_test":"Recompute the final-state ΔγIV − ΔγII with the ceiling in Eq. (6) reduced to 1% (the isobar-constrained upper bound on the CME fraction in Au+Au), keeping all other settings fixed. If the difference falls below ~10^-5 at both σ = 0.3 and 0.7 mb, the quantitative claim in Sec. IV C is not robust. A complementary check: compute the model's no-CME γSS in 30–50% Au+Au and compare with the measured value; if the no-CME result already matches within uncertainty, the 7% calibration is fitting background, not CME.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The central quantitative claim, that ΔγIV − ΔγII is of order 1–2 × 10^-4 after full evolution (Sec. IV C), depends linearly on the 7% ceiling in Eq. (6). That ceiling is fixed by reproducing the γSS correlator in 30–50% Au+Au (Sec. II C), an observable the authors themselves note is contaminated by large v2-driven background (Sec. I, citing the STAR isobar result [25]). The isobar measurement constrains the CME fraction in Au+Au to be small, so matching the full γSS with a CME-injection model may substantially overestimate the true CME strength. Since f scales as |B|_event/|B|_max, all predicted Δγ values, including the claimed visible splitting and the 1–2 × 10^-4 estimate, scale proportionally. The authors provide no uncertainty or sensitivity analysis for this normalization, and the qualitative scheme ordering alone does not establish the quantitative \"clearly non-zero\" claim.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"The paper studies CME-induced charge separation in transversely polarized p+Au collisions at 200 GeV using an AMPT string-melting model with two additions: an impact-parameter-dependent hadron formation-time delay, tuned to reduce the peak Bjorken energy density to about 0.3 GeV/fm3 and to reproduce the PHENIX v2(pT) data, and an event-by-event CME source in which the fraction of quark momentum-exchange scales as |B|_event/|B|_max and is capped at a 7% value calibrated to the Au+Au γSS correlator. The authors define four collision-geometry schemes via the reaction-plane orientation relative to the proton polarization axis, and they report an initial scheme hierarchy tracking B^2, a parton-cascade survival of about 80–90%, a hadronic-phase reduction to about 10–30% of the initial signal, and a final-state inter-scheme difference ΔγIV − ΔγII of order 1–2×10^-4, which they propose as an essentially background-free CME observable.","tokens_in":11208,"tokens_out":6563,"duration_ms":65453,"significance":"If the final-state hierarchy and the inter-scheme difference survive realistic partonic and hadronic evolution, the proposal of using p↑+Au inter-scheme differences as a background-suppressed CME probe is interesting and experimentally testable. The paper has concrete strengths: the model is checked against the PHENIX v2(pT) data and the Bjorken energy-density target; the result is robust to a factor-of-two variation in the parton cross section; and the authors are transparent about the ART hadronic cascade being the dominant source of model dependence. However, the central quantitative claim scales linearly with the externally calibrated 7% CME ceiling, which is anchored to an observable that the authors themselves note is background-dominated, and the paper provides no sensitivity analysis, no control run without CME injection, and no statistical uncertainties on the final-state correlators. The significance of the quantitative prediction is therefore contingent on additional robustness checks.","major_comments":[{"comment":"The quantitative claim that ΔγIV − ΔγII is of order 1–2×10^-4 and 'clearly non-zero' after full evolution scales linearly with the 7% ceiling in Eq. (6). That ceiling is fixed by reproducing the γSS correlator in 30–50% Au+Au [29,43,44], an observable the authors themselves describe as background-dominated, citing the STAR isobar result [25]. If the isobar-constrained CME fraction is smaller than 7%, all quoted Δγ values scale down proportionally and the predicted difference may fall below experimental sensitivity. The paper gives no sensitivity scan over f_max and no isobar-informed upper bound; without such an analysis the central quantitative claim is not established.","section":"Sec. II C / Sec. IV C, Eq. (6)"},{"comment":"The assertion that ΔγIV − ΔγII is an 'essentially pure CME observable' is not demonstrated in the improved model. No control run without the CME exchange is presented, and no explicit estimate is given of the v2-related background contribution to the inter-scheme difference. Because the formation-time delay and the reduced parton cross sections modify the hadronic phase relative to Ref. [29], the small-background conclusion from that earlier setup does not automatically carry over; a no-CME control run or an explicit background calculation should be added to support Eq. (8).","section":"Sec. IV C, Eq. (8)"},{"comment":"The central claims of a 'clearly visible' γOS/γSS splitting and a preserved hierarchy after full evolution are based on central values only; no statistical uncertainties, event counts, or significance tests are reported. Since the final-state effect is at the 10^-4 level, statistical errors are essential to support the word 'clearly' and the 'non-zero' statement in Sec. IV C. Please add error bars or state the number of events and the resulting uncertainty before the detectability claim can be evaluated.","section":"Sec. IV, Figs. 7–18"},{"comment":"The initial-state scheme hierarchy |Δγ|IV ≫ |Δγ|I,III > |Δγ|II is largely built in by construction: Eq. (6) makes the exchange fraction f proportional to |B|_event, and the four schemes are defined so that they pick out different |B| distributions. The final paragraph of Sec. V acknowledges this ('By construction...'), but Sec. IV still presents the hierarchy as a physics message. It should be reframed as a consistency check of the injection mechanism rather than as independent validation of the CME geometry.","section":"Sec. IV A / Sec. II C"},{"comment":"The formation-time delay parameters (A, B, C) are hand-tuned to the energy-density target, and no sensitivity study is presented. Because the delay shifts the onset of the hadronic phase, it can affect the ART-stage dilution that is responsible for most of the signal loss; the final-state survival fraction and the visibility of scheme IV could therefore depend on this tuning. A scan over at least A and C, within values still consistent with the PHENIX v2 data, would show whether the final-state conclusions are robust to this choice.","section":"Sec. II B / Sec. IV C"}],"minor_comments":[{"comment":"Please correct typos: Abstract 'illiptic' → 'elliptic'; Sec. II B 'standand' → 'standard' and 'magnetude' → 'magnitude'; Sec. II A and IV A 'oritation' → 'orientation'; Sec. I 'difficulty' → 'difficulty'.","section":"Throughout"},{"comment":"The pair transverse momentum P+ is defined only in the running text; please display it as an equation, e.g. P+ = (pT,α + pT,β)/2, so that the P+ projections in Figs. 7–12 are self-contained.","section":"Sec. IV A"},{"comment":"The event-plane resolution correction is described briefly; please specify whether the shown v2 values are already corrected for the FVTX event-plane resolution and provide the resolution magnitude, since this is needed to compare the model output directly with the PHENIX data points.","section":"Sec. III B"},{"comment":"Eq. (6) is the key normalization of the paper, but the text does not state the centrality or event-selection details of the Au+Au calibration beyond '30–50%'; please add the relevant kinematic cuts and the statistical precision of that calibration, since the final prediction inherits it linearly.","section":"Sec. II C"}],"recommendation":"major_revision","confidential_remarks":"The main risk is that the 7% ceiling calibration via the background-dominated Au+Au γSS correlator is not a clean anchor for the CME fraction, and the STAR isobar results suggest it could be an upper limit. The paper would be publishable after the authors add a sensitivity scan over the ceiling, a no-CME control run, and statistical uncertainties on the final-state correlators. The work is incremental over the authors' Refs. [28,29], but the event-by-event source and the formation-time tuning add enough new content for a transport-oriented journal in this field."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"First thing to know: this is the third paper in the group's p↑+A CME program, and it is the strongest of the three. The genuinely new bits are the event-by-event CME source that scales with |B|_event/|B|_max, the p+Au retuned formation-time delay, and the stage-by-stage accounting of how the correlator survives. The most useful result is the decomposition: ZPC removes only 10–20% of the initial Δγ, while coalescence plus ART removes most of the rest, leaving 10–30% at the final state. That staging is clearly presented and is the paper's real contribution.\n\nThe paper does several things right. It validates the retuned model against two independent targets – the Bjorken energy density and PHENIX v2(pT) – and the agreement is non-trivial because the formation-time parameters were tuned only on the energy density. The factor-of-two variation in parton cross section provides a reasonable robustness check. And the authors own their main model dependence: they explicitly say ART is the dominant uncertainty. That is honest.\n\nNow the soft spots, in proportion to how soft they actually are. The stress-test note holds up. The 7% ceiling in Eq. (6) is calibrated to the γSS correlator in 30–50% Au+Au, which the authors themselves describe as background-dominated following the STAR isobar result. Because f scales linearly with |B|, every predicted Δγ magnitude, including the 1–2×10^-4 estimate for ΔγIV − ΔγII, scales linearly with that ceiling. If the real CME fraction is below 7%, the 'clearly non-zero' claim shrinks toward zero. The authors provide no sensitivity analysis on this normalization. That is the most serious gap.\n\nThe other issues are minor. The formation-time parameters are hand-tuned; no error bars are reported; the 'essentially background-free' label rests on a self-cited earlier estimate [29]. The initial-state scheme ordering is partly built in by construction, since f scales with |B| and the four schemes select different |B| distributions. The final-state ordering is not trivially inherited, though, so the central qualitative result stands.\n\nMy verdict matches the reader's CONDITIONAL: the paper is a credible, incremental contribution with honest caveats. It is written for the CME/small-system transport community, and a referee should engage with it seriously – but should ask for a sensitivity scan over the 7% ceiling before the quantitative claim is accepted. I would send it to peer review.","headline":"The stage-by-stage survival analysis is the real contribution; the quantitative signal size rests on a 7% calibration that the authors do not stress-test.","tokens_in":11799,"tokens_out":3439,"would_cite":true,"duration_ms":30464,"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":"The paper claims that a difference between two impact-parameter schemes of polarized proton–gold collisions yields an essentially background-free chiral magnetic effect signal that survives the full quark–gluon plasma evolution.","keywords":["chiral magnetic effect","charge separation","polarized proton-gold collisions","AMPT model","gamma correlator","elliptic flow","small collision systems","quark-gluon plasma"],"falsifier":"Measure $\\Delta\\gamma_{\\mathrm{IV}} - \\Delta\\gamma_{\\mathrm{II}}$ in $0$–$5\\%$ central $p^\\uparrow$+Au at $\\sqrt{s_{NN}} = 200\\,\\mathrm{GeV}$ using zero-degree calorimeters to tag the impact-parameter orientation; if the difference is consistent with zero within the expected $1$–$2\\times 10^{-4}$ band, the paper's central claim would be ruled out.","tokens_in":10741,"feed_emoji":"🧲","tokens_out":6060,"duration_ms":48743,"temperature":0.7,"pith_summary":"The paper argues that the chiral magnetic effect (CME)—the separation of electric charge along a transient magnetic field in a quark–gluon plasma—can be isolated in collisions of a transversely polarized proton with a gold nucleus by comparing two impact-parameter orientations. Using an improved transport model, the authors inject an event-by-event CME source whose strength scales with the local magnetic field, and they track how the resulting charge-separation correlator survives parton cascading, quark coalescence, and hadronic rescattering. They find that the difference between the two most separated geometry schemes, $\\Delta\\gamma_{\\mathrm{IV}} - \\Delta\\gamma_{\\mathrm{II}}$, remains at the level of $1$–$2\\times 10^{-4}$ after full evolution, even though most of the signal is dissipated in the hadronic phase. If correct, this offers an essentially background-free observable for the CME in small systems, free of the elliptic-flow backgrounds that have blocked heavy-ion searches.","feed_headline":"A scheme difference isolates the chiral magnetic effect","feed_subtitle":"In polarized proton–gold collisions the inter-scheme difference survives hadronization at about 1–2 x 10^-4.","key_machinery":"The mechanism carries through three ingredients: (1) four collision-geometry schemes defined by the reaction-plane orientation relative to the proton polarization axis, which pick out well-separated values of the magnetic-field strength $B^2$; (2) an event-by-event CME source in which the fraction of quark pairs whose transverse momentum is exchanged scales as $f = 7\\% \\times |\\mathbf{B}|_{\\mathrm{event}}/|\\mathbf{B}|_{\\mathrm{max}}$, capped at the value calibrated to the Au+Au $\\gamma_{\\mathrm{SS}}$ correlator; and (3) an impact-parameter-dependent hadron formation-time delay that reduces the peak energy density to a physical $\\sim 0.3\\,\\mathrm{GeV/fm^3}$. The observable is the three-point correlator $\\gamma_{\\alpha\\beta} = \\langle \\cos(\\phi_\\alpha + \\phi_\\beta - 2\\Psi_{\\mathrm{RP}})\\rangle$ and its charge-dependent difference $\\Delta\\gamma = \\gamma_{\\mathrm{OS}} - \\gamma_{\\mathrm{SS}}$; the key identity is that the scheme difference $\\Delta\\gamma_{\\mathrm{IV}} - \\Delta\\gamma_{\\mathrm{II}}$ cancels flow-driven backgrounds because the background is small in p+Au, leaving $\\Delta\\gamma^{\\mathrm{CME}}_{\\mathrm{IV}} - \\Delta\\gamma^{\\mathrm{CME}}_{\\mathrm{II}}$.","core_discovery":"The central claim is that the inter-scheme difference $\\Delta\\gamma_{\\mathrm{IV}} - \\Delta\\gamma_{\\mathrm{II}}$ — the difference in the charge-dependent azimuthal correlator between two impact-parameter orientations of a polarized proton–gold collision — is an essentially pure CME observable. The paper shows with its improved transport model that while the initial correlator displays a clear hierarchy $|\\Delta\\gamma|_{\\mathrm{IV}} \\gg |\\Delta\\gamma|_{\\mathrm{I}} \\approx |\\Delta\\gamma|_{\\mathrm{III}} > |\\Delta\\gamma|_{\\mathrm{II}}$ tracking $B^2$, the parton cascade preserves $80$–$90\\%$ of the signal, and it is the subsequent hadron-coalescence and hadronic-rescattering stages that dissipate the bulk, leaving roughly $10$–$30\\%$ in the final state. Despite this, the $\\gamma_{\\mathrm{OS}}/\\gamma_{\\mathrm{SS}}$ splitting remains visible and the central-value hierarchy survives, so $\\Delta\\gamma_{\\mathrm{IV}} - \\Delta\\gamma_{\\mathrm{II}}$ is predicted to remain nonzero (order $1$–$2\\times 10^{-4}$) after full evolution. The paper also reports that the correlator is essentially flat in pseudorapidity gap, consistent with a long-range CME source, and that the result is robust against varying the parton cross section by a factor of two.","pith_inferences":["If the scheme difference survives in real data, the same geometric tagging could be applied to other small systems such as d+Au or $^3$He+Au, where the field geometry differs, sharpening the test across collision systems.","A dedicated experimental limit on $\\Delta\\gamma_{\\mathrm{IV}} - \\Delta\\gamma_{\\mathrm{II}}$ could independently bound the $7\\%$ calibration: a null result would either put an upper limit on the CME strength in small systems or force a lower ceiling.","Because the hadronic phase is the dominant source of dilution, the prediction specifically targets improved hadronic-transport models; hybrid hydrodynamics-plus-cascade codes could confirm whether the $\\sim10$–$30\\%$ survival is model-specific or generic.","The flat $\\Delta\\eta$ profile at the final state is a distinctive signature that event-shape engineering in existing p+Au data could search for even without polarization tagging."],"forward_implications":["The difference $\\Delta\\gamma_{\\mathrm{IV}} - \\Delta\\gamma_{\\mathrm{II}}$ is predicted to remain nonzero, at the level of $1$–$2\\times 10^{-4}$, after full partonic and hadronic evolution, making it measurable with impact-parameter tagging.","The scheme hierarchy $|\\Delta\\gamma|_{\\mathrm{IV}} > |\\Delta\\gamma|_{\\mathrm{I,III}} > |\\Delta\\gamma|_{\\mathrm{II}}$ should be visible in the final-state correlator, not only at the initial state.","The correlator is essentially flat in pseudorapidity gap, distinguishing a long-range CME source from short-range $v_2$-related backgrounds.","The result is robust to a factor-of-two change in the parton cross section, suggesting that the pattern is dictated by the magnetic-field geometry.","The bulk of the CME signal is lost in the hadronic rescattering phase, so the final-state observable carries only $\\sim10$–$30\\%$ of the initial charge separation."],"supporting_citations":[{"why":"Supplies the four collision-geometry schemes and the $B^2$ hierarchy across them that the prediction is built on.","marker":"[28]"},{"why":"Prior work proposing $\\Delta\\gamma_{\\mathrm{IV}} - \\Delta\\gamma_{\\mathrm{II}}$ as a background-free observable and the fixed $7\\%$ exchange prescription being replaced here.","marker":"[29]"},{"why":"PHENIX $v_2(p_T)$ data in p+Au that the improved model is validated against.","marker":"[30]"},{"why":"Introduces the impact-parameter-dependent hadron formation-time delay adopted to fix the energy-density overshoot.","marker":"[32]"},{"why":"Provides the local-nuclear-scaling AMPT improvements that underpin the model version used here.","marker":"[33]"},{"why":"Describes the quark momentum-exchange mechanism (swapping $p_y$ of co-moving quark–antiquark pairs) used to inject the CME-like charge separation.","marker":"[42]"},{"why":"STAR Au+Au measurement of the $\\gamma_{\\mathrm{SS}}$ correlator used to fix the $7\\%$ ceiling.","marker":"[43]"},{"why":"Companion STAR measurement providing the same $\\gamma_{\\mathrm{SS}}$ calibration point.","marker":"[44]"}],"fun_headline_variants":["Inter-scheme difference exposes background-free CME in p+Au","Chiral magnetic effect isolated via scheme difference in p+Au","Polarized p+Au: scheme-difference CME probe survives evolution","Δγ_IV−Δγ_II: pure chiral signal in p+Au collisions","Hadronization keeps CME scheme difference visible in p+Au"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The magnitude of the predicted signal rests on a single calibration: the $7\\%$ ceiling on the quark-exchange fraction, set by reproducing the Au+Au $\\gamma_{\\mathrm{SS}}$ correlator in $30$–$50\\%$ centrality — if that ceiling does not represent the true CME fraction in p+Au, all predicted $\\Delta\\gamma$ values scale with it, although the scheme ordering itself would survive.","fun_headline_variants_meta":{"raw":{"variants":["Inter-scheme difference exposes background-free CME in p+Au","Chiral magnetic effect isolated via scheme difference in p+Au","Polarized p+Au: scheme-difference CME probe survives evolution","Δγ_IV−Δγ_II: pure chiral signal in p+Au collisions","Hadronization keeps CME scheme difference visible in p+Au"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000308,"raw_usage":{"total_tokens":1845,"prompt_tokens":1115,"completion_tokens":730,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":731,"completion_tokens_details":{"reasoning_tokens":632}},"tokens_in":731,"tokens_out":730,"duration_ms":6793,"temperature":1.0,"reasoning_tokens":632,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-15T14:18:50.950103+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Measure $\\Delta\\gamma_{\\mathrm{IV}} - \\Delta\\gamma_{\\mathrm{II}}$ in $0$–$5\\%$ central $p^\\uparrow$+Au at $\\sqrt{s_{NN}} = 200\\,\\mathrm{GeV}$ using zero-degree calorimeters to tag the impact-parameter orientation; if the difference is consistent with zero within the expected $1$–$2\\times 10^{-4}$ band, the paper's central claim would be ruled out.","supporting_citations":[{"cited_title":"A new method to clarify contribution of chiral magnetic effect in small collision system $p^{\\uparrow} + A$ involving a transversely polarized proton","cited_arxiv_id":"2408.02939","evidence_quote":"Supplies the four collision-geometry schemes and the $B^2$ hierarchy across them that the prediction is built on."}],"review_version":1}