{"id":"38f05f06-fc40-44a0-a352-593aaad5ef68","arxiv_id":"2504.14607","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":6.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":3,"one_line_summary":"New ACTAR TPC measurements of two-proton emission from 48Ni and 45Fe are compared with Gamow Coupled-Channel and 3-body calculations, favoring small-angle emission but exposing disagreements in half-lives and decay energies.","lead":"An experiment at GANIL used a time projection chamber to record the rare two-proton decay of 48Ni and 45Fe, adding new decay events to earlier measurements. The paper compares the measured proton angles and energies with two theoretical models and finds partial agreement plus unresolved discrepancies.","discovery_kind":"extension","skeptic_critique":{"model":"deepseek-v4-flash","headline":"Angular-distribution 'confirmation' of Vpp is not robust because the GCC model space suppresses the s-wave continuum; the paper's own caveat plus the 48Ni half-life tension leave the central claim conditional.","rationale":"The reader identified the GCC s-wave suppression as the weakest assumption, and the paper itself locates the same limitation in its Conclusions. My independent reading agrees: the angular distribution is the only observable used in the abstract to claim confirmation of the proton-proton interaction strength, and that observable is precisely the one whose theoretical prediction depends on the least-secure model-space assumption. The fact that the 48Ni half-life comparison favors the opposite Vpp value within the same framework shows that the confirmation is not coherent across observables, which reinforces the conditional verdict. I do not see a reason to move beyond CONDITIONAL: the paper is an honest experimental contribution with new data and a clear statement of its own inconsistencies, so rejection is unwarranted. At the same time, the abstract's confirmatory language should not be accepted at face value without the s-wave sensitivity check described above.","tokens_in":10457,"tokens_out":5009,"duration_ms":48308,"concrete_test":"Re-run the GCC calculations for 48Ni and 45Fe with the s1/2 continuum included, or without the 7% s-channel suppression, for both Vpp=100% and Vpp=125%, renormalized to the same Q2p values, and recompute the likelihood comparison against the combined angular data. If Vpp=100 is no longer preferred, or if the two Vpp predictions become statistically indistinguishable, then the abstract's 'confirms the adopted strength' statement must be weakened to a model-dependent consistency claim. As a supplementary check, report the s-wave flux fraction in the emitted two-proton current for both Vpp values to quantify the suppression that the current calculation imposes.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The abstract's central claim rests on a two-point model comparison: GCC calculations with Vpp=100% and Vpp=125%, both performed in a model space in which the s-wave continuum is suppressed. The Theoretical Approach section states that the Woods-Saxon depth was adjusted, 'decreasing the s-channel strength by 7%,' to match the two-proton decay energies. The Conclusions then explicitly admit that 'a contribution of the s-wave continuum, highly suppressed in the present GCC calculations, could possibly retrieve the agreement with the experimental results.' This is a decisive caveat: the s-wave is the channel most sensitive to the proton-proton interaction and to the centrifugal barrier, so the observed preference for Vpp=100 over Vpp=125 in the angular distributions (Tables III and IV) does not confirm the adopted Vpp strength. It shows only that, within a truncated basis and between two hand-picked variants, one matches better. The load is further increased by the internal inconsistency for 48Ni: the same GCC framework favors Vpp=125 when the half-life is compared (Fig. 3a), the opposite of the angular-distribution conclusion. For 45Fe, the angular sample also includes ten events re-identified from 46Fe, so classification risk compounds the model-space risk. The 'confirms' wording is therefore stronger than the evidence supports; the paper is best read as showing consistency under a stated model assumption, not as confirmation of that assumption.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"The paper reports a new experimental study of two-proton radioactivity in 48Ni and 45Fe using ACTAR TPC at GANIL/LISE3. It presents half-lives, branching ratios, total decay energies, individual proton energies, and energy/angular correlations, and compares these observables with new Gamow Coupled-Channel (GCC) calculations and existing 3-body model predictions. The central claim is that the measured two-proton angular distributions confirm the adopted proton-proton interaction strength (100% Vpp) and the predominant small-angle emission, and that the comparisons indicate an f7/2 shell closure in 48Ni and substantial p-orbital occupancy in 45Fe. The paper also reports discrepancies for half-lives, total decay energies, and energy correlations, and explicitly discusses unresolved inconsistencies between experiment and theory.","tokens_in":10717,"tokens_out":5853,"duration_ms":48711,"significance":"If the main claims hold, the paper provides rare and valuable experimental constraints on two-proton continuum correlations, including the first comparison of the 48Ni angular distribution with theoretical calculations. The experimental work is careful: event identification is based on a multi-parameter analysis with cross-checks, proton energies are obtained from track lengths and cross-checked against total charge deposits, and the paper honestly exposes internal inconsistencies. The new GCC calculations for both nuclei extend the theoretical comparison to energy and angular correlations. However, the confirmatory claim is weakened by the model-space suppression of the s-wave continuum, the low event counts for 48Ni, the re-identification of 46Fe events for 45Fe, and the internal tension between the angular-distribution and half-life conclusions. The paper is therefore best read as reporting consistency under stated model assumptions rather than an independent confirmation of the proton-proton interaction strength.","major_comments":[{"comment":"The central claim that the angular distributions 'confirm the adopted strength of the proton-proton interaction' is stronger than the evidence supports. The Conclusions state that 'A contribution of the s-wave continuum, highly suppressed in the present GCC calculations, could possibly retrieve the agreement with the experimental results.' Because the s-wave continuum is precisely the channel most sensitive to the proton-proton interaction and to the centrifugal barrier, the two-point model comparison (Vpp=100% versus Vpp=125%) demonstrates consistency within a truncated model space rather than confirmation of the interaction strength. Please soften the abstract and conclusions accordingly, for example to 'is consistent with' or 'does not contradict'.","section":"Abstract and Conclusions"},{"comment":"For 48Ni, the GCC framework gives opposite preferred Vpp values for different observables: Table III shows that the angular distribution favours Vpp=100% (chi2/dof 0.54 versus 1.38), while the half-life comparison shown in Fig. 3(a) favours Vpp=125%. The paper acknowledges this inconsistency in the text, but the abstract's confirmatory claim does not. Before the angular-distribution result can confirm the interaction strength, the half-life discrepancy must either be resolved or explicitly treated as a model failure that limits the confirmatory power of the angular comparison.","section":"Results, 48Ni, Comparison with theory"},{"comment":"The 48Ni angular-distribution conclusion is based on only three new events combined with previous data. With such low statistics, the difference between chi2/dof=0.54 and 1.38 is not statistically decisive, and the likelihood probabilities in Table III are extremely small for every model (e.g., 4.7e-5 for GCC 100% Vpp), indicating a poor absolute fit. The paper itself notes that 'higher statistics is certainly needed to conclude.' The word 'confirms' in the abstract is therefore not supported by the statistical weight of the data.","section":"Table I and Fig. 2(a)"},{"comment":"For 45Fe, ten of the fifteen angular events are re-identified as 45Fe decays rather than 46Fe decays on the basis of the identification analysis described in the experimental set-up. The contamination study is performed with beta-delayed proton emitters (45Cr, 44Cr, 43Cr, 46Fe, 47Fe) and may not have the same selection sensitivity for two-proton events. Since these ten events carry about two-thirds of the angular distribution shown in Fig. 2(b), the paper should state explicitly how a misclassification of 46Fe events would change the extracted Vpp preference and the p2 occupancy.","section":"Results, 45Fe"},{"comment":"The GCC core-valence potential is adjusted by 'decreasing the s-channel strength by 7%' to align with the experimental two-proton decay energies. Consequently, the comparisons of Q2p between GCC and experiment shown in Table II and Fig. 3 are not independent tests of the model; the potential is fitted to the same observable. This circularity should be acknowledged wherever the Q2p agreement is discussed, or the adjusted parameter should be shown to have negligible effect on the angular correlation predictions.","section":"Theoretical Approach"}],"minor_comments":[{"comment":"Reference [34] contains a sentence ('The same analysis was also performed for 49Ni, but no two-proton events were found in this case') that is not a citation; it should be moved to the main text or a footnote.","section":"References"},{"comment":"The likelihood probability L is quoted without a definition or normalization recipe. Please add a sentence specifying how L is computed and what probability it represents, so that the reader can judge the absolute quality of the fits.","section":"Table III and Table IV"},{"comment":"The figure legend should distinguish the GCC Vpp=100% and Vpp=125% curves and the 3-body omega(p) curves more explicitly; in the current figure the orange and purple curves are difficult to separate, especially in grayscale printing.","section":"Figure 2"},{"comment":"The text reports T1/2(fit)=1.31(37) ms and T1/2(Schmidt)=1.22+0.39/-0.24 ms and adopts the Schmidt value 'to avoid a small dependence from the time range considered for the fit.' Please state the range of half-lives obtained for different fit windows, since this is the justification for discarding the fit result.","section":"Results, 45Fe"},{"comment":"The symbols Vpp=100% and Vpp=125% are used without defining the reference interaction; one sentence explaining that these correspond to scaling the FHT force by those factors (as in [32]) would help non-specialist readers.","section":"Theoretical Approach"}],"recommendation":"major_revision","confidential_remarks":"The manuscript presents genuinely new experimental data and an honest discussion of inconsistencies, and it is well within the scope of the journal. My main concern is the gap between the confirmatory language in the abstract and the model-dependence and low statistics of the angular-distribution comparison; a major revision that softens the claims and adds a sensitivity analysis would address this."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Read it. The genuinely new things are modest but real: three new 2p events from 48Ni (added to Pomorski's four), the first beta-delayed 3p branch observed for 48Ni, six new 45Fe events plus ten re-identified from 46Fe, and the first angular-distribution comparison against Gamow coupled-channel (GCC) calculations. The event reconstruction looks careful, and the paper is admirably candid about its own inconsistencies — the TPC Q2p values sit systematically below silicon values, the 48Ni angular preference for Vpp=100% conflicts with the half-life preference for Vpp=125%, and the s-wave suppression caveat is stated openly. That honesty is the best part of the paper.\n\nThe soft spot is the abstract's 'confirms the adopted strength' claim. It overstates what the evidence supports. The angular evidence is statistically thin — three new 48Ni events, 15 total for 45Fe including ten from the neighbouring isotope — and the model comparison is two hand-picked GCC variants in a basis where the s-wave continuum is strongly suppressed. The paper itself notes that adding s-wave could restore agreement. On top of that, the Woods-Saxon depth is adjusted to reproduce Q2p, so the Q2p agreement is not independent, and for 48Ni the half-life points the other way. So the data are consistent with Vpp=100% under the adopted model assumptions, not a confirmation of the interaction strength.\n\nThe Q2p discrepancy between TPC and silicon measurements is an unresolved systematic that the authors flag and partly test with simulations. Good that they checked; still, until it is understood, the total-energy comparisons should be treated as tentative. The re-identification of ten 46Fe events as 45Fe is plausible given the cross-contamination they describe, but it makes the 45Fe angular distribution riskier than the paper fully admits.\n\nThe citation pattern is standard for a compact experimental letter; no obvious missing key references. Who is this for? The two-proton radioactivity community. They will want the new events and the first GCC angular comparison. The paper deserves a serious referee — the data are hard to get and the honesty is rare — but the 'confirms' wording needs to be softened to something like 'is consistent with' and the model-space caveat needs to move from the conclusions into the abstract's claim.\n\nRecommendation: send to peer review. Expect revision, mostly tone and framing, not new data.","headline":"Honest experimental paper with new events and a first GCC angular comparison, but the abstract's 'confirms' claim outruns the statistics and the model-space caveat.","tokens_in":11433,"tokens_out":2025,"would_cite":true,"duration_ms":18224,"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 two-proton angular distributions of 48Ni and 45Fe match Gamow coupled-channel calculations with the standard proton-proton interaction strength, supporting small-angle emission and constraining valence shell structure.","keywords":["two-proton radioactivity","proton-proton correlations","Gamow Coupled-Channel","48Ni","45Fe","angular distribution","proton drip line","time projection chamber"],"falsifier":"Measure the 48Ni two-proton angular distribution with at least 30 events and compare the binned distribution to GCC predictions at 100% and 125% $V_{pp}$; if the small-angle peak is reproduced only by the 100% curve, the claimed interaction-strength confirmation stands, whereas a compatible fit from the 125% curve would leave the strength underdetermined.","tokens_in":10238,"feed_emoji":"⚛️","tokens_out":8036,"duration_ms":65965,"temperature":0.7,"pith_summary":"This paper reports new measurements of the two-proton radioactivity of 48Ni and 45Fe and uses them to test how well current few-body models capture the decay. The central claim is that the angular distribution between the two emitted protons, combined with earlier data, agrees with Gamow coupled-channel (GCC) calculations using the standard proton-proton interaction strength, and favors the expected small-angle emission in both nuclei. The same angular data, viewed through 3-body model predictions, point to a closed $f_{7/2}$ shell in 48Ni and a substantial $p$-orbital occupancy in 45Fe. The paper also finds that half-lives, total decay energies, and the proton energy-sharing distribution are not reproduced by the same models, so the full two-proton emission process remains incompletely understood.","feed_headline":"Two-proton decay angles confirm proton-proton force strength","feed_subtitle":"New data on 48Ni and 45Fe match small-angle emission and constrain shell structure, but half-lives still disagree.","key_machinery":"The load-bearing object is the two-proton angular distribution, i.e., the distribution of the opening angle $\\theta_{pp}$ between the two emitted protons, reconstructed in three dimensions from the tracks left in a time-projection chamber. The theory side is the Gamow Coupled-Channel (GCC) framework, which treats the emitter as a spherical daughter core plus two valence protons and uses the Berggren ensemble of bound, resonant, and scattering states, together with a finite-range Furutani-Horiuchi-Tamagaki proton-proton force and a Woods-Saxon core potential. The paper varies the proton-proton interaction strength between 100% and 125% of the nominal value, and compares the predicted angular distributions with the 3-body model predictions, which are parametrized by the $p$-orbital occupancy $\\omega(p)$. Agreement is quantified by likelihood probabilities and chi-square per degree of freedom.","core_discovery":"The paper's central claim is that the two-proton angular correlation is a discriminating observable for the decay dynamics: comparing the measured $\\theta_{pp}$ distributions for 48Ni and 45Fe with new GCC calculations and with 3-body model predictions supports the standard proton-proton interaction strength ($V_{pp}=100\\%$) for both nuclei and a predominantly small-angle emission geometry. For 48Ni, the comparison with 3-body predictions indicates a low $p$-orbital occupancy, consistent with the $f_{7/2}$ shell closure expected for a doubly magic nucleus; for 45Fe, the comparison requires a substantial $p$-orbital occupancy. These structural conclusions are presented as the paper's positive result, while the discrepancies among half-life, total decay energy, and energy-sharing observables are acknowledged as unresolved complexities that may involve $s$-wave continuum contributions or different decay configurations.","pith_inferences":["If $s$-wave continuum contributions are responsible for the half-life and total-energy discrepancies, then angular distributions alone underdetermine the proton-proton interaction strength; energy and width observables must be fitted jointly.","The narrower-than-predicted proton energy-sharing distribution in 45Fe suggests a decay configuration with a larger centrifugal barrier; a testable extension would be to measure the same distribution in the two-proton emitter 54Zn, where the $p$-orbital occupancy is predicted to be smaller.","A tandem time-projection chamber plus silicon detector measurement, suggested by the authors, would settle whether the total decay-energy offset is instrumental; if confirmed, previous silicon-based decay-energy values for 48Ni and 45Fe may need downward revision, with consequences for mass extrapolations."],"forward_implications":["If the angular-distribution agreement holds, the standard proton-proton interaction strength is validated in the continuum regime for two-proton emitters, not just in bound nuclear structure.","For 48Ni, the data support a closed $f_{7/2}$ shell, reinforcing its doubly magic character from a decay-correlation observable.","For 45Fe, the angular distribution requires substantial $p$-orbital occupancy, implying configuration mixing in the valence system.","The failure of the same models to reproduce half-lives, total decay energies, and energy sharing means angular correlations alone are not sufficient to pin down the decay mechanism; additional observables or model extensions, such as $s$-wave continuum contributions, are needed.","A systematic offset between TPC-based and silicon-based total decay-energy values, if real, would affect comparisons to mass predictions and needs a dedicated tandem measurement."],"supporting_citations":[{"why":"Supplies the earlier 48Ni two-proton angle measurements that are combined with the present data for the angular-distribution comparison.","marker":"[27]"},{"why":"Supplies the earlier 45Fe two-proton angle measurements and branching ratio that the present work adds to and compares with.","marker":"[3]"},{"why":"Provides the 3-body model predictions for angular distributions used in the shell-occupancy comparison.","marker":"[5]"},{"why":"Defines the Gamow Coupled-Channel framework used for the new calculations.","marker":"[14]"},{"why":"Provides the finite-range proton-proton interaction whose strength is varied as $V_{pp}=100\\%$ and $125\\%$.","marker":"[19]"},{"why":"Supplies the nucleon-nucleon interaction parametrization used to set the proton-proton strength variation.","marker":"[32]"},{"why":"Supplies previous 48Ni and 45Fe half-life and total decay-energy values used in the comparison and in identifying the TPC/silicon offset.","marker":"[23]"},{"why":"Provides the flux-current method used to compute decay widths from the GCC wave function.","marker":"[17]"}],"fun_headline_variants":["Two-proton angles confirm force, half-lives resist theory","Small-angle proton pairs match theory, half-lives don't","48Ni and 45Fe two-proton angles: force confirmed, lifetimes elusive","Two-proton decay: angles validate interaction, half-lives challenge theory"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The conclusion assumes that the $s$-wave continuum contribution is strongly suppressed in the GCC model space; if $s$-wave components contribute non-negligibly, the inferred proton-proton interaction strength and orbital occupancies from the angular distributions would not be reliable.","fun_headline_variants_meta":{"raw":{"variants":["Two-proton angles confirm force, half-lives resist theory","Small-angle proton pairs match theory, half-lives don't","48Ni and 45Fe two-proton angles: force confirmed, lifetimes elusive","Two-proton decay: angles validate interaction, half-lives challenge theory"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.001281,"raw_usage":{"total_tokens":5225,"prompt_tokens":926,"completion_tokens":4299,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":542,"completion_tokens_details":{"reasoning_tokens":4222}},"tokens_in":542,"tokens_out":4299,"duration_ms":28464,"temperature":1.0,"reasoning_tokens":4222,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-16T11:44:48.788408+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Measure the 48Ni two-proton angular distribution with at least 30 events and compare the binned distribution to GCC predictions at 100% and 125% $V_{pp}$; if the small-angle peak is reproduced only by the 100% curve, the claimed interaction-strength confirmation stands, whereas a compatible fit from the 125% curve would leave the strength underdetermined.","supporting_citations":[{"cited_title":"Pomorski et al","cited_arxiv_id":null,"evidence_quote":"Supplies the earlier 48Ni two-proton angle measurements that are combined with the present data for the angular-distribution comparison."},{"cited_title":"Miernik et al","cited_arxiv_id":null,"evidence_quote":"Supplies the earlier 45Fe two-proton angle measurements and branching ratio that the present work adds to and compares with."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Provides the 3-body model predictions for angular distributions used in the shell-occupancy comparison."},{"cited_title":"Furutani et al","cited_arxiv_id":null,"evidence_quote":"Provides the finite-range proton-proton interaction whose strength is varied as $V_{pp}=100\\%$ and $125\\%$."},{"cited_title":"Thomson et al","cited_arxiv_id":null,"evidence_quote":"Supplies the nucleon-nucleon interaction parametrization used to set the proton-proton strength variation."},{"cited_title":"Dossat et al","cited_arxiv_id":null,"evidence_quote":"Supplies previous 48Ni and 45Fe half-life and total decay-energy values used in the comparison and in identifying the TPC/silicon offset."}],"review_version":1}