{"id":"8132bfda-20e0-4ef5-976e-f2894d9782d7","arxiv_id":"2607.10644","paper_version":1,"verdict":"ACCEPT","confidence":"HIGH","novelty_score":6.5,"correctness_risk":"low","formal_verification":"none","parameter_count":3,"one_line_summary":"First joint C/O double-differential νμ CC0πNp cross sections in δpT–δαT and pN–cosθμ show current generators fail to describe the data.","lead":"T2K's ND280 measured the first joint double-differential cross sections for muon-neutrino pionless charged-current interactions on carbon and oxygen using kinematic-imbalance variables. The data expose clear failures in current nuclear models that limit oscillation precision.","discovery_kind":"extension","skeptic_critique":{"model":"grok-4.5","headline":"No significant objection identified","rationale":"The reader correctly isolates the only soft spot (the δpT–αT post-fit p-value) and correctly notes that Appendix A already demonstrates its practical irrelevance for the signal. The physics-pseudo-data suite (Sec. V.C.2) further shows that even large signal- and background-model reweightings (SF\to LFG/CRPA, FSI \times3, GENIE reweight, etc.) are recovered within uncertainties, confirming that the free-template construction is not secretly locked to the NEUT prior. Statistical dominance of the uncertainties and the quantitative model-by-model χ^{2} tables supply independent support for the claim that generators are inadequate and that KI observables discriminate. No stronger load-bearing concern exists; the verdict remains ACCEPT.","tokens_in":51711,"tokens_out":493,"duration_ms":5870,"concrete_test":"Re-extract the δpT–αT signal cross sections with the free-background-template configuration of Appendix A and recompute the χ^{2}/p-values of Tables VI–IX against the same five generator models; if any model’s joint C+O p-value changes by more than ~0.1 or crosses the 0.05 threshold relative to the published values, the background-model residual would affect the model-discrimination claim.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The central claim—that current generators fail to describe the joint C/O double-differential KI data while the same observables discriminate nuclear-effect contributions—rests on a free-signal-template extraction whose model independence is supported by extensive pseudo-data tests (Table V, all p-values ≈ 1) and by the Appendix A study showing that freeing background templates raises the δpT–αT p-value from ~0.008 to ~0.09 without shifting the extracted signal beyond a fraction of the reported uncertainty. The low p-value is therefore a statement about residual background-model tension, not a bias in the signal cross sections that enter the model comparisons of Sec. VII. No internal inconsistency or untested assumption that would overturn the claim is present.","agreement_with_reader":"agree"},"referee_report":{"model":"grok-4.5","summary":"The paper reports the first joint measurement of νμ CC0πNp cross sections on carbon and oxygen with the T2K ND280 detector, presented as double-differential distributions in the kinematic-imbalance spaces δpT–δαT and pN–cosθμ. Signal selection, control samples for the dominant CC1π+ background, phase-space constraints, a full systematic covariance (detector, flux, interaction modeling, target nucleons), and a free-signal-template unfolding with GUNDAM are documented in detail. Coverage tests and extensive physics pseudo-data fits (SF→LFG/CRPA, FSI strength, GENIE reweight, etc.) support model independence of the extracted cross sections. The data are then compared with a suite of NEUT and GENIE nuclear models; several configurations are disfavored while others (NEUT SF/ED-RMF, GENIE SuSAv2+hN) describe the joint C/O data better, illustrating the discriminating power of the KI observables.","tokens_in":51923,"tokens_out":690,"duration_ms":8316,"significance":"If the result holds, the measurement supplies a high-value, joint C/O double-differential data set in observables that isolate initial-state motion, multi-nucleon correlations and FSI. The free-signal-template extraction, control-sample constraints, and exhaustive pseudo-data validation (Table V, all p ≈ 1) constitute a transparent and largely model-independent procedure. The explicit demonstration that current generators fail in intermediate δpT/pN regions while still discriminating among nuclear-effect models is directly relevant to T2K, Hyper-Kamiokande and DUNE oscillation systematics. The accompanying data release further strengthens the paper’s utility for generator development.","major_comments":[],"minor_comments":[{"comment":"Sec. VI.A and Appendix A: the low post-fit p-value (~0.008) in the δpT–δαT fit is thoroughly investigated and shown not to bias the signal; a short cross-reference in the main text to the quantitative bound (maximum bin-wise shift < 60 % of the uncertainty) would help readers who stop at Sec. VI.","section":null},{"comment":"Figs. 11–19: the vertical scale of the oxygen panels is sometimes compressed relative to carbon; a common scale or an explicit note would ease visual comparison of the two targets.","section":null},{"comment":"Table I and Sec. IV.B: the residual non-C/O and OOFV fractions are small but non-zero; a one-sentence statement of how they are treated in the unfolding (subtracted via MC or absorbed into the free templates) would remove any residual ambiguity.","section":null},{"comment":"Eq. (4) and the definition of ⟨ϵ⟩p: the numerical values 26.1 MeV (C) and 23.0 MeV (O) are taken from Ref. [29]; a brief remark that the uncertainty on these mean excitation energies is negligible compared with the reported cross-section uncertainties would be useful.","section":null}],"recommendation":"accept","confidential_remarks":"The manuscript is long and dense, but the technical content is of high quality and the central claim is solidly supported. I see no reason to delay publication; the minor presentation points can be handled at the proof stage if the journal prefers."},"author_rebuttal":null,"desk_editor":{"model":"grok-4.5","letter":"This is the first simultaneous carbon–oxygen double-differential measurement of νμ CC0πNp in the two KI spaces δpT–δαT and pN–cosθμ. That is the real product: a joint C/O data set that can be used directly for generator tuning and for the nuclear-effect systematics that still dominate T2K/Hyper-K/DUNE oscillation analyses.\n\nWhat they did well is the extraction chain. Free signal templates, control samples for the dominant CC1π+ background, full detector/flux/interaction covariance, coverage tests, and a battery of physics pseudo-data (SF→LFG/CRPA, FSI strength, GENIE reweight, etc.) all land with high p-values. The low post-fit p-value (~0.008) in the δpT–δαT fit is investigated in Appendix A; freeing background templates raises it to ~0.09 without moving the signal beyond a fraction of the reported uncertainty. So the low p-value is a statement about residual background-model tension, not a bias in the cross sections that enter the model comparisons. The quantitative χ2 tables against NEUT (SF, ED-RMF, LFG) and GENIE (CRPA, SuSAv2, hA/hN/Bertini) are the most useful part of the paper for people who actually write generators.\n\nSoft spots are real but proportionate. Statistics dominate every bin (20–70 % total uncertainty). Oxygen is thinner than carbon. The background parameterization that produces the low p-value is the same one used in the latest T2K oscillation paper, so the tension is not unique to this analysis, but it does mean the “model-independent” claim still rests on the adequacy of those priors. None of this overturns the central claim that current generators fail to describe the joint data while the KI variables discriminate nuclear-effect contributions.\n\nThis is for people who tune NEUT/GENIE or who need exclusive C/O inputs for oscillation systematics. It is not a broad-impact particle-physics result, but it is a clean, well-documented data product from a major collaboration with a public data release. I would send it to peer review without hesitation; the referee time is justified.","headline":"First joint C/O double-differential KI cross sections from T2K; solid extraction, useful model discrimination, statistics-limited but ready for generator work.","tokens_in":54823,"tokens_out":548,"would_cite":true,"duration_ms":9220,"reading_group":"yes","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":[],"model":"grok-4.5","headline":"First joint carbon-oxygen double-differential KI cross sections show neutrino-nucleus models fail to describe T2K data.","keywords":["neutrino-nucleus cross section","kinematic imbalance","CC0πNp","T2K ND280","carbon oxygen targets","double-differential measurement","nuclear effects","final-state interactions"],"falsifier":"A future high-statistics measurement in the same KI spaces that finds a generator model simultaneously describing both the δpT peak at low δαT and the high-pN tail at large muon scattering angle within the reported uncertainties.","tokens_in":52663,"feed_emoji":"⚛️","tokens_out":997,"duration_ms":16183,"temperature":0.7,"pith_summary":"This paper reports the first joint measurement of muon-neutrino charged-current interactions that leave no pions and at least one proton on both carbon and oxygen, expressed as double-differential cross sections in two kinematic-imbalance spaces. Those spaces are built from the transverse momentum imbalance between the muon and the leading proton and from the inferred initial nucleon momentum versus muon angle. The measurement is performed with the T2K near detector and extracts the signal with a free-template fit that is validated to be largely independent of the interaction model used as a prior. The extracted cross sections disagree with every current generator model in at least part of the phase space, while the same observables cleanly separate regions dominated by initial-state nucleon motion from regions dominated by final-state interactions and multi-nucleon currents. Because carbon and oxygen are the principal targets in long-baseline oscillation experiments, the result supplies a direct, model-independent constraint that must be satisfied by any improved nuclear model if oscillation-parameter precision is to improve.","feed_headline":"Neutrino models fail first joint carbon-oxygen KI test","feed_subtitle":"Double-differential T2K cross sections expose gaps that limit oscillation precision","key_machinery":"Double-differential kinematic-imbalance (KI) observables — specifically δpT–δαT and pN–cosθμ reconstructed from the muon and leading proton — which map distinct nuclear processes onto distinct regions of phase space and thereby allow a free-template, model-independent extraction of the joint carbon-oxygen signal.","core_discovery":"Current neutrino-nucleus interaction generators do not adequately describe the measured double-differential CC0πNp cross sections on carbon and oxygen in the δpT–δαT and pN–cosθμ spaces; the same kinematic-imbalance observables possess strong discriminating power among the nuclear-effect contributions that currently limit oscillation analyses.","pith_inferences":["Because oxygen is the far-detector target, a model that fails oxygen KI data while fitting carbon will still bias Hyper-Kamiokande and DUNE oscillation parameters.","The same free-template method can be reapplied to antineutrino and electron-neutrino beams once statistics allow, testing lepton-flavor universality of nuclear effects.","Discrepancies that persist after reweighting final-state-interaction strength suggest that the problem is not merely cascade tuning but the treatment of two-body currents already at the primary vertex."],"forward_implications":["Generator builders must revise nuclear ground-state, multi-nucleon and final-state-interaction modelling until both carbon and oxygen KI distributions are reproduced simultaneously.","Oscillation analyses that rely on the same interaction models inherit a residual bias that can only be reduced by incorporating these double-differential constraints.","The upgraded ND280 Super-FGD, with larger active mass and better low-momentum proton acceptance, will convert the present statistics-limited result into a precision test of nuclear models.","Regions of intermediate δpT and pN remain under-predicted, pointing to a need for stronger multi-nucleon or continuum-random-phase-approximation contributions."],"fun_headline_variants":["T2K joint C-O KI data expose neutrino model shortfalls","First dual-target double-diff cross sections challenge nuclear models","KI observables show generators fail on T2K carbon-oxygen data","Neutrino models miss T2K CC0πNp cross sections on C and O","Joint carbon-oxygen KI results demand improved interaction models"],"cache_read_input_tokens":49280,"weakest_assumption_plain":"The background model constrained by control samples is flexible enough that residual tension with data (post-fit p-value ~0.008 in one space) does not bias the extracted signal cross section.","fun_headline_variants_meta":{"raw":{"variants":["T2K joint C-O KI data expose neutrino model shortfalls","First dual-target double-diff cross sections challenge nuclear models","KI observables show generators fail on T2K carbon-oxygen data","Neutrino models miss T2K CC0πNp cross sections on C and O","Joint carbon-oxygen KI results demand improved interaction models"]},"model":"grok-4.5","effort":"low","cost_usd":0.003866,"raw_usage":{"total_tokens":1171,"prompt_tokens":694,"num_sources_used":0,"completion_tokens":94,"cost_in_usd_ticks":38660000,"prompt_tokens_details":{"text_tokens":694,"audio_tokens":0,"image_tokens":0,"cached_tokens":256},"completion_tokens_details":{"audio_tokens":0,"reasoning_tokens":383,"accepted_prediction_tokens":0,"rejected_prediction_tokens":0}},"tokens_in":694,"tokens_out":94,"duration_ms":4807,"temperature":1.0,"reasoning_tokens":383,"cache_read_input_tokens":256,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-07-14T10:14:59.120809+00:00","model_set":{"reader":"grok-4.5"},"falsifier":"A future high-statistics measurement in the same KI spaces that finds a generator model simultaneously describing both the δpT peak at low δαT and the high-pN tail at large muon scattering angle within the reported uncertainties.","supporting_citations":[],"review_version":1}