{"id":"565afdc2-ccec-4b86-b5aa-8cf2929fc47f","arxiv_id":"2608.04997","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":6.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":7,"one_line_summary":"New electrocouplings for five nucleon resonances in the third resonance region were extracted from CLAS pi+pi- p cross sections using the JM23 reaction model.","lead":"This paper reports the first extraction of nucleon resonance electroexcitation amplitudes from pi+pi- p electroproduction data in the third resonance region at Q2 between 2 and 5 GeV2. The results include the first high-Q2 amplitudes for the Delta(1700) and N(1720) resonances and new evidence for a second N(1720)-like state.","discovery_kind":"extension","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The new N'(1720) claim is not tested against fits without the state, and per-bin non-resonant flexibility could absorb the same strength; this leaves the central resonance-isolation claim under-supported.","rationale":"The reader's weakest assumption is that the JM23 non-resonant amplitudes do not absorb the s-channel resonant strength; my concern is a specific, testable case of that general assumption, centered on the new N'(1720) state that is part of the paper's strongest claim. I do not see a reason to change the CONDITIONAL verdict: the paper has real independent support in the consistency between piN and pi+pi-p results for N(1675) and N(1680), and the across-W consistency of several extracted electrocouplings is a positive signal. However, the paper's claim to have 'conclusively demonstrated' the new state (Sec. IV E) goes beyond what is shown, because no fit without that state is presented and the per-bin non-resonant flexibility provides a plausible absorption mechanism. The proposed test directly addresses whether the central construction is secure: if removing N'(1720) degrades the fit clearly and leaves the other electrocouplings unchanged, the claim is strengthened; if not, the claim and the associated resonance parameters should be presented as model-dependent rather than established. The verdict remains conditional pending such an exclusion test or an alternative model comparison.","tokens_in":32834,"tokens_out":3126,"duration_ms":40635,"concrete_test":"Repeat the Sec. III fits in the 1.61-1.71 and 1.66-1.76 GeV windows with the N'(1720) contribution removed, allowing the same non-resonant parameters to vary (and, if needed, relaxing the 20% prior on the direct-2pi normalizations). Compare the resulting chi2/d.p. values with Table VII and examine whether the extracted N(1720), Delta(1700), N(1675), and N(1680) electrocouplings shift beyond their quoted uncertainties. If chi2/d.p. stays below about 1.0, or if the other electrocouplings move substantially, the N'(1720) claim and the reliability of the amplitudes extracted in this window are not established. A secondary check: re-fit with N'(1720) present but with an alternative parameterization of the pi+N(1520) or direct-2pi non-resonant terms to test stability of the resonance parameters.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The most load-bearing step is the assertion in Sec. IV E that a new N'(1720)3/2+ is required at Q^2 = 2-5 GeV^2. The fits in Sec. III always include both N(1720) and N'(1720), and the selection criterion (chi2/d.p. < 1, Table VII) is applied only within this two-state model. No alternative fit with N'(1720) removed is reported, so the paper does not demonstrate that the data require the new state. This matters because the non-resonant amplitudes are renormalized per (W,Q^2) bin: the fitted magnitudes of the contact terms, the pi+N(1520) channel, and up to six direct-2pi amplitudes per Q^2 bin are all free (Sec. III). A broad resonance-like enhancement near W ~ 1.72 GeV could in principle be absorbed by these flexible backgrounds, with the conventional N(1720) and Delta(1700) parameters shifting to compensate. The paper's counterargument that Q^2-independent hadronic widths for N'(1720) prove an s-channel origin (Sec. IV E) is not decisive: the resonant electrocouplings carry the Q^2 dependence, while the non-resonant normalizations are adjusted independently in each bin, so the observed success of Q^2-independent masses and widths does not establish uniqueness. The cross-channel consistency for N(1675) and N(1680) is genuine positive evidence, but those states are not the ones whose existence or isolation is most in question.","agreement_with_reader":"partial"},"referee_report":{"model":"deepseek-v4-flash","summary":"The paper analyzes CLAS pi+pi-p electroproduction differential cross sections at W=1.56-1.76 GeV and Q2=2.0-5.0 GeV2 with the JM23 reaction model, extracting gamma_v p N* electrocouplings and hadronic decay parameters for Delta(1600)3/2+, N(1675)5/2-, N(1680)5/2+, Delta(1700)3/2-, N(1720)3/2+, and a new N'(1720)3/2+ state. The results for N(1675) and N(1680) are reported to be consistent with independent CLAS piN analyses, and the paper presents the first electrocouplings for Delta(1700) and N(1720) at Q2>2.0 GeV2. The main evidence for the new N'(1720) state is the good fit quality with Q2-independent masses and widths across the full Q2 range, together with differences in decay patterns and electrocouplings relative to the conventional N(1720).","tokens_in":33430,"tokens_out":4924,"duration_ms":56780,"significance":"If the extraction is reliable, the paper provides a substantial extension of the empirical knowledge of nucleon resonance electroexcitation into the third resonance region at high Q2, with genuinely useful constraints for continuum Schwinger methods, quark models, and future coupled-channel analyses. The cross-channel consistency for N(1675) and N(1680) between piN and pi+pi-p analyses is a real strength, as is the internal consistency across overlapping W intervals. The claimed observation of a new N'(1720)3/2+ state with a measured Q2 evolution would be an important result for the physics of 'missing' resonances. However, the significance is tempered by the strong model dependence of the extraction and by the absence of a direct test of whether the data actually require the new state.","major_comments":[{"comment":"The central claim that the new N'(1720)3/2+ state contributes to the pi+pi-p cross sections at Q2=2-5 GeV2 is not supported by a fit that excludes the state. All fits in Section III include N'(1720) in the resonance set (Table IV), and the selection criterion chi2/d.p.<1 in Table VII is applied only within this two-state model. To demonstrate that the data require the new state, the paper should report the chi2/d.p. and the resulting N(1720) parameters from a fit without N'(1720), and show whether the non-resonant amplitudes can compensate for its absence. Without such a test, the statement in Section IV E that the data 'conclusively demonstrated' contributions from both states is overstated.","section":"Section IV E and Table XV"},{"comment":"The description of the fit selection procedure is not sufficient to assess the statistical meaning of the extracted parameter uncertainties. The text says 'we selected the computed cross sections that were closest to the data and satisfied the condition chi2/d.p. < chi2_max/d.p.', but it does not state how the trial parameter sets are generated, how many fits enter the selection, or whether the selected set provides coverage of the parameter space. If only fits below an acceptance threshold are kept, the central values in Eqs. (3)-(5) and the RMS dispersions in Tables XI-XVIII may be biased and the uncertainties underestimated. Please specify the fitting algorithm, the number of trials, and the criteria used to define the 'closest' fits.","section":"Section III, Table VII"},{"comment":"The argument that Q2-independent hadronic masses and widths for N'(1720) provide 'nearly model-independent evidence' for its existence is not decisive. The non-resonant amplitudes are renormalized independently in each (W,Q2) bin through the fitted magnitudes of contact terms, pi+N(1520), pi+N(1680), and direct-2pi mechanisms (Section III), so the fitted electrocouplings carry the Q2 dependence and a broad resonance-like enhancement near W~1.72 GeV could in principle be absorbed by these flexible backgrounds. A sharper test would be a fit with the non-resonant parameterization fixed from a global analysis or varied in a controlled way to see whether the N'(1720) amplitude remains required.","section":"Section IV E"},{"comment":"There is an internal inconsistency in the treatment of N(1720)-N'(1720) mixing. Section II B states that transitions N(1720)3/2+ <-> N'(1720)3/2+ are incorporated into the JM23 model through the dressed resonance propagator, while Section IV E states that the distinct decay patterns of the two states 'prevents their mixing'. These statements cannot both be true. Please clarify which implementation is actually used, and quantify how the mixing transition affects the extracted electrocouplings of the two states.","section":"Section II B and Section IV E"}],"minor_comments":[{"comment":"In the first sentence, 'electroexcitation amplitudes or the gamma_vpN* electrocouplings' should be 'electroexcitation amplitudes of the gamma_vpN* electrocouplings' or similar, since 'or' appears to be a typo.","section":"Abstract"},{"comment":"The text appropriately cautions that the small uncertainties on the masses and widths of N(1675) and N(1680) should be interpreted with care because other decay modes were kept fixed; this caveat should also be stated in the conclusions where the Q2-independence of the widths is used as evidence of an s-channel origin.","section":"Section IV B, Tables IX and X"},{"comment":"The captions say that 'only the statistical uncertainties are shown, except for the particular data points ... dominated by systematic uncertainties', but the figures do not identify which points those are. Please add an explicit marker or explanation so the reader can distinguish the two classes of data points.","section":"Figures 3-5"},{"comment":"Reference [75] appears to be a 1980 proceedings contribution on group-theoretical methods, not a work on lattice QCD, and does not seem to support the statement that progress is being made in lattice simulations of resonance physics. Please check and correct this citation.","section":"Conclusions and Outlook"}],"recommendation":"major_revision","confidential_remarks":"The paper is within the scope of Physical Review C and the data analysis is substantial, but I am not convinced that the new N'(1720) claim is established without a fit excluding the state. The fit-selection procedure also needs to be documented more completely. These are fixable in revision, so I recommend major revision rather than rejection. The authors should be encouraged to provide the requested negative-result fit and a more transparent error treatment."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Colleague — the headline: this is a solid data-analysis paper that fills a genuine kinematic gap, and the cross-channel check for N(1675) and N(1680) is the strongest part. But the claim of a new N'(1720)3/2+ state is not yet demonstrated.\n\nWhat's new: first pi+pi-p extractions of electrocouplings for Delta(1700), N(1720), and N'(1720) at Q2>2 GeV2, and first pi-pi-N results for N(1675) and N(1680) in this W range. The numbers are tabulated with uncertainties derived from the spread across fits in overlapping W bins. The consistency between the pi-N and pi+pi-p channels for N(1675) and N(1680) is genuine positive evidence: two very different reaction models give compatible amplitudes over 2<Q2<5 GeV2. The Delta(1600) results also confirm the earlier CSM prediction, which was made before these data were used, so that part is not circular.\n\nThe soft spots are about the new state and the model systematics. The paper never shows a fit with N'(1720) removed. Given that the non-resonant amplitudes have per-(W,Q2) normalizations, a broad enhancement near 1.72 GeV could in principle be absorbed by those backgrounds. The Q2-independent hadronic widths for N'(1720) are suggestive, but not decisive, because the electrocouplings carry the Q2 dependence. The fit selection procedure (chi2/d.p. below a chosen max, then choose the closest) is a mild form of selection bias; the quoted uncertainties are RMS over selected fits, which likely understate the model dependence. The tails of 1.9-2.0 GeV states are fixed, and the uncertainty from that choice is not quantified. These are real issues, but they are not fatal for the better-established resonances.\n\nThe citation pattern is fine — mostly CLAS's own prior work plus the relevant reaction-model literature. The paper is careful in places, e.g., it cautions against overinterpreting the small mass/width uncertainties.\n\nVerdict: worth refereeing, but major revision. A referee should ask for (1) a fit excluding N'(1720) with a likelihood/chi2 comparison, (2) a stability test of the non-resonant normalization freedom, and (3) a softer statement of the new-state claim unless the test is passed. The N(1675)/N(1680) results and the Delta(1700) first extraction can be published without that, though.","headline":"Fills a real kinematic gap and the N(1675)/N(1680) cross-channel consistency is solid, but the N'(1720) claim needs a fit without the state.","tokens_in":33915,"tokens_out":2853,"would_cite":true,"duration_ms":33908,"reading_group":"maybe","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":["13.40.-f","14.20.Gk","12.40.Nn"],"model":"deepseek-v4-flash","headline":"First electroexcitation amplitudes of six nucleon resonances are extracted from pi+pi-p data, including a new N'(1720)3/2+ state.","keywords":["nucleon resonance electrocouplings","third resonance region","pi+ pi- p electroproduction","JM23 reaction model","N'(1720)3/2+ state","dynamical chiral symmetry breaking","emergence of hadron mass","electron scattering"],"falsifier":"Refit the same nine one-fold differential cross sections with an alternative non-resonant parameterization, for example with different $t$-channel forms or additional contact-term degrees of freedom, and check whether the extracted $A_{1/2}$, $A_{3/2}$, and $S_{1/2}$ for $\\Delta(1700)3/2^-$ and $N'(1720)3/2^+$ move outside the quoted uncertainties.","tokens_in":32632,"feed_emoji":"⚛️","tokens_out":8603,"duration_ms":87622,"temperature":0.7,"pith_summary":"Working from electron-scattering data on the reaction $ep\\to e'\\pi^+\\pi^-p'$, the paper aims to establish the first values of the $\\gamma_v p N^*$ electroexcitation amplitudes (electrocouplings) for the nucleon resonances $\\Delta(1600)3/2^+$, $N(1675)5/2^-$, $N(1680)5/2^+$, $\\Delta(1700)3/2^-$, $N(1720)3/2^+$, and the newer $N'(1720)3/2^+$ in the third resonance region, with $W$ from 1.56 to 1.76 GeV and $Q^2$ from 2.0 to 5.0 GeV$^2$. It reports that the extracted amplitudes for $N(1675)5/2^-$ and $N(1680)5/2^+$ agree with those from independent single-pion analyses, which is the paper's main cross-check that resonant strength is being isolated correctly. For $\\Delta(1700)3/2^-$ and $N(1720)3/2^+$ these are the first electrocouplings available above $Q^2 = 2.0$ GeV$^2$, and the analysis finds clear contributions from the $N'(1720)3/2^+$ state. If the extraction is right, these amplitudes become empirical constraints on how nucleon excited states are built from dressed quarks and on how hadron mass emerges in strong QCD.","feed_headline":"First electrocouplings of six nucleon resonances from pi+pi-p data","feed_subtitle":"Single-pion analyses agree for N(1675) and N(1680); a new N'(1720) 3/2+ state shows up.","key_machinery":"The central object is the set of $\\gamma_v p N^*$ electrocouplings $A_{1/2}$, $A_{3/2}$, and $S_{1/2}$, the photon-transition amplitudes that encode how virtual photons excite each nucleon resonance. The machinery that carries the extraction is the JM23 reaction model, a phenomenological description of $\\gamma_v p \\to \\pi^+\\pi^-p'$ built from $\\pi^-\\Delta^{++}$, $\\pi^+\\Delta^0$, $\\rho p$, $\\pi^+N(1520)$, and $\\pi^+N(1680)$ subchannels plus direct two-pion mechanisms, with $s$-channel resonances described by a unitarized Breit-Wigner ansatz. Fits to nine one-fold differential cross sections in overlapping $W$ intervals allow the resonant amplitudes to be isolated and averaged, and the consistency of parameters across those intervals is the main internal check on the separation.","core_discovery":"The paper's central claim is that the JM23 reaction model, fitted to nine one-fold $\\pi^+\\pi^-p$ differential cross sections measured on a proton target, can separate resonant from non-resonant contributions in the third resonance region and thereby yield the $\\gamma_v p N^*$ electrocouplings $A_{1/2}$, $A_{3/2}$, and $S_{1/2}$ for six resonances. The results for $N(1675)5/2^-$ and $N(1680)5/2^+$ are consistent with the amplitudes obtained independently from $\\pi N$ electroproduction, and the model requires both the established $N(1720)3/2^+$ and a second, nearby $N'(1720)3/2^+$ state with distinct decay patterns to describe the data up to $Q^2 = 5.0$ GeV$^2$. The paper further argues that the resonance masses and hadronic decay widths extracted from the fits do not vary with $Q^2$, which it reads as evidence that these states are genuine $s$-channel excitations with an inner core of three dressed quarks.","pith_inferences":["If the same fit strategy is carried into the 12-GeV energy regime, the $\\pi^+\\pi^-p$ channel could map electrocouplings for other 'missing' resonances over a wider $Q^2$ range, since the method does not rely on the $\\pi N$ decay branch that makes such states hard to see in single-pion data.","The striking difference between the longitudinal-dominated $\\Delta(1700)3/2^-$ excitation and the transverse-dominated $\\Delta(1232)3/2^+$ excitation, if confirmed, would make chiral-partner pairs a sharper diagnostic of the mechanism behind hadron mass than the resonance spectrum alone.","A direct test would be to rerun the same fits with a completely different non-resonant model; if the extracted amplitudes move outside the quoted uncertainties, the model-dependence is larger than the paper's internal consistency checks suggest.","The near-coincidence of results across overlapping $W$ intervals hints that the dominant uncertainty budget is set by the non-resonant parameterization rather than by the data statistics, so future experiments should focus on kinematics that constrain the background."],"forward_implications":["First electrocouplings for $\\Delta(1700)3/2^-$ and $N(1720)3/2^+$ become available for $Q^2 > 2$ GeV$^2$, where these resonances' dominant $\\pi\\pi N$ decays make this channel the primary probe.","The agreement between $\\pi N$ and $\\pi^+\\pi^-p$ extractions for $N(1675)5/2^-$ and $N(1680)5/2^+$ supports using either channel independently for resonance parameters in the third resonance region.","The $N'(1720)3/2^+$ state, previously seen only below $Q^2 = 1.5$ GeV$^2$, is shown to persist up to $Q^2 = 5$ GeV$^2$ with $Q^2$-independent mass and widths, strengthening the case that it is a real baryon state.","The $Q^2$-independent masses and hadronic widths of the six resonances become empirical evidence that they are excited as $s$-channel states with a dressed-quark core, providing direct input for calculations of hadron mass emergence from strong QCD.","The measured $Q^2$ evolution of the electrocouplings, including the longitudinal dominance of $\\Delta(1700)3/2^-$, offers a new testing ground for models of dynamical chiral symmetry breaking."],"supporting_citations":[{"why":"Supplies the measured $\\pi^+\\pi^-p$ differential cross sections that are fitted for the resonance parameters.","marker":"[37]"},{"why":"Provides the JM23 reaction model and its previous extraction of $\\Delta(1600)3/2^+$ electrocouplings, which this analysis extends.","marker":"[15]"},{"why":"Gives the independent $\\pi N$ electrocouplings for $N(1675)5/2^-$ and $N(1680)5/2^+$ used for the cross-channel consistency check.","marker":"[9]"},{"why":"Establishes the $N'(1720)3/2^+$ state and its low-$Q^2$ parameters, which the present analysis confirms at higher $Q^2$.","marker":"[38]"},{"why":"Supplies the published resonance masses, widths, and branching-fraction ranges that constrain the fit parameters.","marker":"[42]"},{"why":"Defines the underlying model amplitudes for the $\\pi^+\\pi^-p$ subchannels on which JM23 is built.","marker":"[12]"}],"fun_headline_variants":["Six nucleon resonance electrocouplings from π+π-p data","First resonance amplitudes from double-pion electroproduction at CLAS","New N'(1720) state revealed in pion-pair electroproduction","Electrocouplings for six resonances: π+π-p vs πN agreement","Third resonance region: electrocouplings from π+π-p cross sections"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The load-bearing premise is that the JM23 model's non-resonant amplitudes, which are adjusted in the fits, describe the background well enough that the $s$-channel resonant strength is not absorbed into those background terms; if that fails, the extracted electrocouplings are not genuine resonance parameters.","fun_headline_variants_meta":{"raw":{"variants":["Six nucleon resonance electrocouplings from π+π-p data","First resonance amplitudes from double-pion electroproduction at CLAS","New N'(1720) state revealed in pion-pair electroproduction","Electrocouplings for six resonances: π+π-p vs πN agreement","Third resonance region: electrocouplings from π+π-p cross sections"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000286,"raw_usage":{"total_tokens":1825,"prompt_tokens":1229,"completion_tokens":596,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":845,"completion_tokens_details":{"reasoning_tokens":500}},"tokens_in":845,"tokens_out":596,"duration_ms":6390,"temperature":1.0,"reasoning_tokens":500,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-06T11:53:45.832862+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Refit the same nine one-fold differential cross sections with an alternative non-resonant parameterization, for example with different $t$-channel forms or additional contact-term degrees of freedom, and check whether the extracted $A_{1/2}$, $A_{3/2}$, and $S_{1/2}$ for $\\Delta(1700)3/2^-$ and $N'(1720)3/2^+$ move outside the quoted uncertainties.","supporting_citations":[{"cited_title":"Measurements of $\\gamma_v p \\to \\pi^+ \\pi^- p'$ Cross Sections with the CLAS Detector for $Q^{2}$ from 2.0--5.0~GeV$^{2}$ and $W$ from 1.400--2.125~GeV","cited_arxiv_id":"2607.06793","evidence_quote":"Supplies the measured $\\pi^+\\pi^-p$ differential cross sections that are fitted for the resonance parameters."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Provides the JM23 reaction model and its previous extraction of $\\Delta(1600)3/2^+$ electrocouplings, which this analysis extends."},{"cited_title":"Parket al.(CLAS Collaboration), Phys","cited_arxiv_id":null,"evidence_quote":"Gives the independent $\\pi N$ electrocouplings for $N(1675)5/2^-$ and $N(1680)5/2^+$ used for the cross-channel consistency check."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Defines the underlying model amplitudes for the $\\pi^+\\pi^-p$ subchannels on which JM23 is built."}],"review_version":1}