{"id":"628077ca-e99c-4161-a9e6-e4b21156f464","arxiv_id":"2506.03934","paper_version":2,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":5.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":5,"one_line_summary":"SuSAM-v2 separates longitudinal and transverse scaling functions, makes the transverse one depend on momentum transfer, and improves fits to low-q electron data and T2K neutrino data.","lead":"This paper builds SuSAM-v2, a new version of a nuclear scattering model that treats the longitudinal and transverse responses of nuclei to electrons with separate, momentum-dependent scaling functions. The model improves predictions for neutrino-nucleus cross sections used in neutrino oscillation experiments such as T2K.","discovery_kind":"extension","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The fT extraction in Eq. (23) absorbs any unsubtracted SRC and any MEC-model error; since the same 2p2h channels are later added to the neutrino predictions, the claimed improvement may be partly a double-counting artifact.","rationale":"This is a useful and honest phenomenological update: fL is fitted to longitudinal response data, fT is an analytic q-dependent Gaussian, and comparisons with separated responses, T2K, and MINERvA are presented. The main scientific content is the claim that the q-dependence of fT is determined by the 1p1h transverse response and that this improves neutrino predictions. The load-bearing premise is the subtraction in Eq. (23): whatever remains after removing the MEC 2p2h model and the fL-based longitudinal contribution is assigned to 1p1h transverse strength. As written, the SRC/correlated-pair 2p2h term is not subtracted in Eq. (23), while it is added back later in the neutrino calculations. Thus the fitted Table II coefficients can absorb the SRC tail and any MEC-model error, and the neutrino prediction can double count these channels. This is not an accusation of inconsistency; it is a concrete ambiguity in the extraction pipeline. The proposed test settles it: redo the extraction with and without the SRC subtraction and with an independent 2p2h model, and see whether Table II and the T2K comparison move materially. If they do, the central claim of improved neutrino prediction should be conditional on the 2p2h model; if they do not, the concern is resolved. The reader identified the same root cause, and the resulting conditional verdict remains appropriate.","tokens_in":19209,"tokens_out":7077,"duration_ms":66134,"concrete_test":"Re-run the Section III.b extraction with Eq. (23) modified to also subtract the SRC/correlated-pair 2p2h term of Refs. [40,41], and separately replace the RMF-MEC subtraction with an independent 2p2h model (e.g., Nieves et al., Phys. Rev. C 83, 045501). Re-fit Table II and recompute the T2K double-differential predictions (Fig. 7). If a(q), b(q), c(q) shift by more than the bin-to-bin variation in Table II, or if the T2K description changes by more than the visible differences in Fig. 7, the neutrino improvement is not robust to the 2p2h subtraction assumption.","verdict_should_be":"UNCHANGED","load_bearing_attack":"Section III.b defines the empirical transverse scaling function via Eq. (23): the inclusive electron cross section is reduced by the RMF-MEC 2p2h calculation of Refs. [41,42] and by the fL-determined longitudinal contribution, and the remainder is declared 1p1h transverse. This is load-bearing because the central claim is that the fitted a(q), b(q), c(q) in Table II represent genuine QE transverse strength and that SuSAM-v2 therefore improves neutrino predictions. As written, Eq. (23) subtracts only the MEC 2p2h contribution; the SRC/correlated-pair 2p2h term of Refs. [40,41] is not subtracted at this stage. Any SRC tail and any systematic error in the MEC subtraction can therefore migrate into the fitted QE Gaussian. SuSAM-v2 then evaluates neutrino cross sections as fT-based 1p1h responses plus additive MEC and SRC 2p2h terms (Section IV.B, Figs. 7-8). If fT already contains part of the EM 2p2h strength, the weak predictions may double count or mistune that strength, especially because weak MEC and SRC enter with different axial and isospin couplings. The T2K improvement could thus be an artifact of the subtraction scheme rather than more accurate longitudinal/transverse separation. The claim that fT is obtained in a model-independent way is too strong, since the extraction depends on a specific 2p2h model and on the visual rejection of low-q points.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"The paper presents SuSAM-v2, a superscaling model for quasielastic lepton-nucleus scattering. Whereas SuSAM-v1 used a single scaling function fitted to inclusive (e,e') cross sections, v2 first fits a longitudinal scaling function fL*(ψ*) to separated longitudinal response data for 12C (Eq. (22), Table I) and then extracts a transverse scaling function fT*(ψ*,q) from inclusive electron cross sections by subtracting a 2p2h-MEC contribution and the fL-based longitudinal part (Eqs. (23)-(25)). The transverse function is fitted bin-by-bin in q as a single Gaussian, and the resulting parameters a(q), b(q), c(q) are smoothed with Fermi functions (Tables II and III). The model is compared with separated RL and RT responses, inclusive (e,e') spectra, and flux-averaged charged-current neutrino cross sections from T2K and MINERvA, with 2p2h (MEC and SRC) contributions added. The authors claim the model simultaneously describes electron responses and cross sections and improves neutrino predictions relative to SuSAM-v1.","tokens_in":19641,"tokens_out":7751,"duration_ms":69971,"significance":"The proposed analytic, q-dependent transverse scaling function is a potentially useful object: if robustly extracted, it offers a transparent and efficient parametrization for event generators and a natural route to improving low-q neutrino predictions. The paper correctly identifies longitudinal/transverse separation as the key limitation of v1, and the neutrino comparisons in Figs. 7-8 are independent of the electron fit, which makes them a genuine test. The analysis of axial-form-factor sensitivity in Figs. 9-10 is also a strength. However, as presented, the electron-scattering validation is largely in-sample: fT is constructed from the same inclusive data that are later compared in Figs. 5-6, no uncertainties are reported for the fitted parameters, the low-q selection is visual, and the neutrino predictions inherit assumptions about the subtracted 2p2h strength. The paper's significance therefore depends on whether these points can be addressed with out-of-sample checks and sensitivity analyses.","major_comments":[{"comment":"The claim that the agreement with RT in Fig. 5 constitutes a 'genuine prediction' is not supported by the construction. In Eq. (23) the experimental transverse response is defined by subtracting the 2p2h-MEC contribution and the fL-determined longitudinal part from the inclusive cross section, and Eq. (25) fits fT to these same data. Consequently, the RT panels in Fig. 5 and the inclusive cross sections in Fig. 6 are in-sample consistency checks rather than independent tests. This bears directly on the central claim, stated in the abstract, that the model 'simultaneously describes' inclusive cross sections and both response functions. Please provide an out-of-sample validation, for example by refitting fT after excluding selected q-bins or kinematics and then predicting the excluded data, and report residuals or chi-square values for data not used in the fit.","section":"Sections III.b and IV.A (Eqs. (23)-(25), Fig. 5)"},{"comment":"The q-dependence of fT is the main new content of the paper, but the evidence for it is presented without uncertainties. The a(q), b(q), c(q) values in Table II are fitted bin-by-bin from roughly 3000 points, and the paper states that for low-q intervals 'certain data points that clearly do not exhibit scaling behavior were not taken into account' after visual inspection. Without parameter errors, per-bin point counts, and a reproducible selection criterion, the reader cannot judge whether the 18-bin model is overfitting, whether the low-q reduction is statistically significant, or whether the improvement over SuSAM-v1 is meaningful. Please report fit uncertainties (including propagation into the Fermi-function parameters of Table III), the number of points per q-bin, and a quantitative description of the data-selection procedure.","section":"Section III.b, Tables II and III"},{"comment":"There is a potential double-counting or mismatch of 2p2h strength between the electron extraction and the neutrino predictions. Eq. (23) subtracts only the RMF-MEC 2p2h contribution from the inclusive cross section before fT is fitted; the SRC/correlated-pair 2p2h contribution of Refs. [40,41] is not subtracted at this stage. The neutrino cross sections in Figs. 7-8 then add both MEC and SRC 2p2h contributions on top of the fT-based 1p1h responses. If any part of the subtracted or unsubtracted 2p2h strength leaks into the fitted QE Gaussian, the weak predictions inherit that leakage; because the weak MEC and SRC channels enter with different axial and isospin couplings than the electromagnetic channels, the claimed T2K improvement could be an artifact of the subtraction scheme. The manuscript should clarify whether the Gaussian decomposition removes SRC strength from fT, and should test the sensitivity of the neutrino results to the assumed 2p2h subtraction model.","section":"Section III.b and Section IV.B"}],"minor_comments":[{"comment":"The sentence preceding Eq. (22) says the parameters ai, bi, ci are 'center', 'width', and 'height', respectively, but in Eq. (22) a is the height, b the center, and c the width; the wording should be corrected.","section":"Section III.a, Eq. (22) and Table I"},{"comment":"The text says the transverse scaling function is obtained by dividing (RT)exp by the single-nucleon transverse response, but the denominator shown is the prefactor Z r_T^p + N r_T^n of Eq. (19), not the response itself; the wording should be aligned with Eqs. (18)-(19).","section":"Section III.b, Eq. (24)"},{"comment":"fT is described as extracted from 'purely transverse data', whereas Eqs. (23)-(25) show it is extracted from inclusive cross sections after subtracting a 2p2h model and the longitudinal contribution; the wording should be adjusted.","section":"Abstract"},{"comment":"The abbreviation 'RFGM*' is not defined in the caption or in the text; please define it explicitly.","section":"Fig. 2 caption"},{"comment":"The combined citation 'Ref. [3, 48]' should be split into two separate references or formatted consistently with the journal style.","section":"Fig. 1 and Fig. 5 captions"},{"comment":"The assumption that the same fT applies to both RT and RT' is stated without comment; given that this is a new ingredient of v2, a brief justification or reference to the corresponding SuSA-v2 treatment would help the reader assess the weak predictions.","section":"Section IV.B"}],"recommendation":"major_revision","confidential_remarks":"The manuscript is within the journal's scope and represents a reasonable incremental contribution to neutrino-nucleus phenomenology. The main concern is not the formalism but the validation protocol: the electron-scattering comparisons are in-sample, and the neutrino improvement may be coupled to the 2p2h subtraction scheme. I would encourage the editor to seek a revision that adds out-of-sample checks and uncertainty estimates rather than rejecting. I also note that the manuscript relies heavily on the authors' own previous 2p2h models (Refs. [40-42]) for the subtraction that defines fT; this is legitimate but increases the need for a sensitivity analysis."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Bottom line: this is a worthwhile incremental contribution. It separates fL and fT in the SuSAM effective-mass framework, gives the transverse function a smooth q-dependence via Fermi-parametrized Gaussians, and shows real improvement in low-q electron responses and in T2K comparisons. The analytic form is a practical advantage for event-generator use, and the paper is honest about being a phenomenological update.\n\nThe main soft spot is exactly the one you flagged: the fT extraction in Eq. (23) subtracts only the MEC 2p2h term, not the SRC term, and then fits the remainder to inclusive cross sections. So the \"transverse prediction\" in Fig. 5 is partly a refit, not a clean out-of-sample result. The claim that RT is a genuine prediction is overstated: fT is constrained by the same inclusive cross sections that define RT. The neutrino comparisons are more independent, but they inherit whatever systematic error is baked into fT from the 2p2h subtraction and from the visual rejection of low-q points. The paper gives no uncertainties for a(q), b(q), c(q), which makes it hard to judge how significant the improvement over v1 actually is.\n\nThe double-counting concern in the stress-test is plausible. If fT already contains part of the EM SRC strength (because only MEC was subtracted), then adding SRC additively in the neutrino channel can double count. The authors should address this explicitly, either by subtracting both 2p2h pieces in the extraction or by showing that the fitted QE Gaussian does not include the SRC tail. This is the main thing I'd want fixed in revision.\n\nThe formalism is standard and the paper is clearly written. The citation pattern is fine; the paper builds directly on the SuSAM line and SuSA-v2.\n\nWho should read it: anyone working on neutrino event generators or oscillation systematics who wants a compact, portable QE response. It's not a breakthrough, but it's a solid engineering improvement. I'd send it to review, with a request that the authors clarify the in-sample status and the SRC subtraction.","headline":"A useful analytic upgrade of the SuSAM scaling model, with a q-dependent transverse function and better low-q behavior, but the validation is partly in-sample and the fT extraction absorbs model-dependent 2p2h chunks.","tokens_in":20102,"tokens_out":4325,"would_cite":false,"duration_ms":37719,"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":"A revised superscaling model splits the nuclear response into a longitudinal function fitted to separated data and a transverse function that must carry explicit momentum-transfer dependence, improving low-q electron and neutrino…","keywords":["superscaling","quasielastic electron scattering","nuclear response functions","effective mass","transverse scaling function","momentum transfer dependence","neutrino-nucleus scattering","two-particle-two-hole excitations"],"falsifier":"Re-derive $f_T$ from the same electron dataset after replacing the model calculation of two-nucleon meson-exchange currents with an independent microscopic calculation; if the fitted Gaussian parameters $a(q)$, $b(q)$, $c(q)$ shift enough to change the predicted low-angle neutrino cross sections beyond the experimental error bars, then the extracted transverse function is an artifact of that subtraction.","tokens_in":19029,"feed_emoji":"⚛️","tokens_out":12926,"duration_ms":111615,"temperature":0.7,"pith_summary":"This paper builds an improved superscaling model of quasielastic lepton–nucleus scattering, SuSAM-v2. Superscaling is the phenomenological idea that the nuclear response factorizes into a single-nucleon cross section and a function of one scaling variable $\\psi^*$; the improvement is to replace the single universal function of the previous version with two independent ones, a longitudinal $f_L(\\psi^*)$ fitted directly to separated longitudinal response data and a transverse $f_T(\\psi^*,q)$ extracted from inclusive cross-section data after subtracting the longitudinal part and two-nucleon (2p2h) contributions. The central finding is that $f_T$ must depend explicitly on the momentum transfer $q$ to describe all kinematics, so it is parametrized as a single Gaussian whose height, width, and peak position are smooth Fermi functions of $q$. With this separation, the model simultaneously describes the inclusive quasielastic electron cross section and the separated longitudinal and transverse responses, and it improves charged-current neutrino predictions relative to SuSAM-v1, especially at low momentum transfers. The practical payoff is that an analytic, $q$-dependent transverse scaling function is cheap and transparent enough for use in neutrino event generators and oscillation analyses.","feed_headline":"Splitting nuclear responses fixes low-energy neutrino predictions","feed_subtitle":"A q-dependent transverse scaling function replaces one universal curve and sharpens fits to electron and neutrino data.","key_machinery":"The carrying mechanism is the factored form of the response, $R_K = (\\text{single-nucleon prefactor}) \\times \\text{scaling function}$, built on the relativistic Fermi gas with effective mass $M^*$ and the scaling variable $\\psi^*$. The new content is two scaling functions: $f_L(\\psi^*)$, a sum of two Gaussians fitted to separated longitudinal data, and $f_T(\\psi^*,q)$, a single Gaussian per $q$-bin whose parameters $a(q)$, $b(q)$, $c(q)$ are each parametrized by a Fermi function. The factorization turns the nuclear response into a product of known single-nucleon kinematics and a phenomenological function, so separating responses in the neutrino channel reduces to assigning $f_L$ to the CC, CL, and LL responses and $f_T$ to the $T$ and $T'$ responses. That identification — longitudinal response inherits the $L$ scaling function, transverse and axial-transverse interference inherit the $q$-dependent $T$ function — is what carries the improved neutrino prediction.","core_discovery":"SuSAM-v2 claims that the transverse nuclear response in quasielastic scattering is not governed by the same scaling function as the longitudinal response, and that the transverse scaling function carries an unavoidable dependence on the momentum transfer $q$. The evidence is assembled by fitting $f_L(\\psi^*)$ to separated longitudinal response data for $^{12}$C and then using roughly three thousand inclusive electron cross-section points to extract $f_T$ per $q$-bin, subtracting the fixed longitudinal contribution, a microscopic two-nucleon meson-exchange current term, and a short-range correlation contribution, while masking the resonance and deep-inelastic backgrounds with additional Gaussians. The authors report that the resulting model reproduces the separated transverse response — which was not directly fitted — across $q = 300$, $380$, and $570$ MeV/c, and that flux-averaged charged-current neutrino cross sections for T2K and MINERvA are described as well as or better than with SuSAM-v1. Their formulation deliberately keeps $f_T$ analytic, with coefficients $a(q)$, $b(q)$, $c(q)$ written as Fermi functions of $q$, so the model can be implemented without numerical tables.","pith_inferences":["If the $q$-dependence of $f_T$ mostly encodes final-state interactions, the same analytic parametrization may need target-specific adjustments beyond effective-mass scaling; applying the extraction to heavier nuclei from electron data alone and then comparing with their neutrino data would test that.","Because the extraction subtracts a model calculation of two-nucleon processes, the neutrino success of SuSAM-v2 doubles as a test of that two-nucleon model; a future calculation that changes the subtracted strength would renormalize $f_T$ and could move the low-angle neutrino predictions.","The explicit momentum-transfer dependence means traditional zeroth-kind scaling fails in the transverse channel, so neutrino event generators should treat the transverse response as kinematics-dependent rather than universal.","Comparing this analytic $f_T$ with the numerically defined transverse function obtained from full relativistic mean-field calculations would quantify how much of the apparent $q$-dependence is nuclear-physics content versus modeling choice."],"forward_implications":["SuSAM-v2 reproduces the separated longitudinal and transverse response functions for $^{12}$C at $q = 300$, $380$, and $570$ MeV/c, where SuSAM-v1 failed, making the transverse description a genuine consequence of the fit rather than a direct fit to $R_T$.","In neutrino scattering, the corrected relative weight of longitudinal and transverse responses lowers the predicted cross section at small muon angles in the T2K bins, bringing it into better agreement with data.","MINERvA comparisons show both model versions describe the high-energy data well, so the practical gain of v2 is concentrated at lower momentum transfer, where the $q$-dependence of $f_T$ matters.","Two-nucleon (2p2h) terms from meson-exchange currents and short-range correlations remain necessary, contributing roughly 20 percent of the T2K cross section and about 30 percent in the MINERvA bins.","Replacing the dipole axial form factor with newer parametrizations changes the predicted quasielastic peak cross section by up to 25 percent, so the response separation alone does not remove axial-vector uncertainty."],"supporting_citations":[{"why":"Establishes the SuSAM baseline: the effective-mass scaling variable, the Gaussian ansatz, and the global fits to inclusive quasielastic data that SuSAM-v2 refines.","marker":"[33, 34]"},{"why":"Provides the separated longitudinal response data for carbon used to fit $f_L(\\psi^*)$.","marker":"[3, 48]"},{"why":"Supplies the roughly three thousand inclusive carbon electron-scattering cross-section points from which $f_T$ is extracted in each momentum-transfer bin.","marker":"[46, 47]"},{"why":"Supplies the microscopic two-nucleon meson-exchange current responses subtracted from the inclusive data before isolating the transverse one-body response.","marker":"[41, 42]"},{"why":"Supplies the semi-empirical short-range correlation and one-body two-nucleon term subtracted alongside the meson-exchange currents in the extraction.","marker":"[40, 41]"},{"why":"Defines the neutrino-nucleus response decomposition and kinematic coefficients used to convert the electron-derived scaling functions into charged-current cross sections.","marker":"[44]"},{"why":"Provides the T2K flux-averaged charged-current neutrino data used to demonstrate the low-angle improvement over SuSAM-v1.","marker":"[53]"},{"why":"Provides the MINERvA hydrocarbon-target charged-current data used to test the model at high momentum transfer.","marker":"[54]"}],"fun_headline_variants":["Separating nuclear responses sharpens neutrino predictions","Transverse nuclear response needs momentum dependence for better fits","q-dependent transverse scaling improves neutrino cross-section predictions","Improved superscaling with q-dependent transverse response"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The transverse scaling function is defined as whatever remains after subtracting the longitudinal response and two-nucleon background contributions from the measured cross sections; if those subtracted models are wrong, the fitted function and every neutrino prediction built on it inherit the error.","fun_headline_variants_meta":{"raw":{"variants":["Separating nuclear responses sharpens neutrino predictions","Transverse nuclear response needs momentum dependence for better fits","q-dependent transverse scaling improves neutrino cross-section predictions","Improved superscaling with q-dependent transverse response"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000574,"raw_usage":{"total_tokens":2723,"prompt_tokens":973,"completion_tokens":1750,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":589,"completion_tokens_details":{"reasoning_tokens":1691}},"tokens_in":589,"tokens_out":1750,"duration_ms":15264,"temperature":1.0,"reasoning_tokens":1691,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-07T10:53:29.042485+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Re-derive $f_T$ from the same electron dataset after replacing the model calculation of two-nucleon meson-exchange currents with an independent microscopic calculation; if the fitted Gaussian parameters $a(q)$, $b(q)$, $c(q)$ shift enough to change the predicted low-angle neutrino cross sections beyond the experimental error bars, then the extracted transverse function is an artifact of that subtraction.","supporting_citations":[{"cited_title":"Amaro, M.B","cited_arxiv_id":null,"evidence_quote":"Defines the neutrino-nucleus response decomposition and kinematic coefficients used to convert the electron-derived scaling functions into charged-current cross sections."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Provides the T2K flux-averaged charged-current neutrino data used to demonstrate the low-angle improvement over SuSAM-v1."},{"cited_title":"Abe et al., (T2K Collaboration), Phys","cited_arxiv_id":null,"evidence_quote":"Provides the MINERvA hydrocarbon-target charged-current data used to test the model at high momentum transfer."}],"review_version":1}