{"id":"d7b6cdc9-e403-4525-b8df-1784d0945817","arxiv_id":"2508.06954","paper_version":1,"verdict":"UNVERDICTED","confidence":"LOW","novelty_score":5.0,"correctness_risk":"unknown","formal_verification":"none","parameter_count":0,"one_line_summary":"An inclusive measurement of the top quark width at FCC-ee could bound exotic top decay branching fractions without assuming any specific decay final state.","lead":"This paper proposes using FCC-ee, a future electron-positron collider, to measure the top quark's total decay width inclusively and so set model-independent limits on exotic top quark decays. The value would be a clean, final-state-independent bound on new physics coupled to the top quark, built from the cleanliness of lepton collisions.","discovery_kind":"new_method","skeptic_critique":{"model":"deepseek-v4-flash","headline":"Model-independent branching-fraction limit fails if new physics also modifies the dominant t→Wb partial width; the 'excess equals exotic branching' step needs an unstated assumption.","rationale":"The reader correctly identified that the argument assumes production is independent of decay and that systematics are controlled. My concern is more specific: even granting those assumptions, the inference from a total-width excess to an exotic branching fraction requires the dominant SM partial width to be unaffected by new physics. This is not a minor technicality; it directly undermines the 'model-independent' qualifier in the central claim. The reader's weakest_assumption mentions 'attributed entirely to exotic branching fractions' but does not separate the possibility that new physics alters the t→Wb width. I agree partially because the reader's general formulation covers some of this, but the specific mechanism—modified dominant width compensating an exotic channel—is not articulated. Since the full text is unavailable, I cannot verify whether the paper addresses this in the body, but the abstract as written states the claim unconditionally. The verdict should be conditional on this assumption being explicitly stated and either defended or removed from the claim.","tokens_in":5407,"tokens_out":4592,"duration_ms":58998,"concrete_test":"Construct a minimal benchmark: add an effective dipole operator O_tW = (Q σ^{μν} t) τ^I φ W_{μν}^I / Λ^2 that changes Γ(t→Wb) by an amount δ, and add a single exotic channel t→cZ with width Γ_ex. Choose parameters so Γ_ex = -δ (destructive or compensating), making Γ_total exactly equal to the SM value. Simulate the proposed FCC-ee threshold scan and apply the paper's inclusive extraction. If the method reports no bound on BR(t→cZ), then the model-independence claim is refuted. Alternatively, check whether any equation in the paper explicitly subtracts a measured/SM Γ(t→Wb) separately from the total-width excess.","verdict_should_be":"CONDITIONAL","load_bearing_attack":"The central claim is that measuring the inclusive top-quark width at FCC-ee and comparing it with the SM prediction establishes model-independent bounds on rare/exotic top branching fractions. This works only if the SM partial width Γ(t→Wb) is unchanged by new physics. The measured total width is Γ_t = Γ_SM + Γ_BSM, where Γ_BSM includes both new decay channels and any modification to the dominant t→Wb vertex (e.g., anomalous couplings or mixing). If new physics reduces Γ(t→Wb) while adding an exotic channel, Γ_t can remain equal to Γ_SM, so the inclusive method would report no exotic excess despite a nonzero branching fraction. Conversely, an enhanced t→Wb coupling would mimic an exotic excess. Thus the method is not model-independent in the sense claimed; it bounds the total non-SM width contribution, not specifically rare-decay branching fractions, unless the SM partial width is assumed to be unmodified. This is a logical gap in the abstract's phrasing, and the body should either justify the assumption or weaken the claim.","agreement_with_reader":"partial"},"referee_report":{"model":"deepseek-v4-flash","summary":"The abstract claims that by studying direct t-tbar production at the FCC-ee and measuring the inclusive top-quark width, one can detect any exotic decay contribution and establish model-independent limits on rare top-quark branching fractions. The argument is that the measured total width, compared with the accurately known standard-model prediction, bounds any non-SM partial width regardless of the final state. However, the supplied full text is not this paper; it is an unrelated manuscript on dataset discovery. Thus no derivations, simulations, systematic uncertainties, or numerical results are available to support the abstract's claims.","tokens_in":5651,"tokens_out":2004,"duration_ms":22333,"significance":"If the proposed method works, it would be a valuable complement to direct searches for rare top decays at a future e+e- collider. The inclusive-width approach could in principle be model-independent with respect to the exotic final state. However, the manuscript as submitted cannot be evaluated: the body text is a different paper. Within the abstract alone, the central model-independence claim also requires an unstated assumption about the dominant t→Wb partial width. These issues prevent the current submission from being accepted or meaningfully revised.","major_comments":[{"comment":"The full text of the submission is not the paper described in the abstract. It is a paper on dataset discovery, not a study of top-quark physics at FCC-ee. No equations, simulations, detector assumptions, error budget, or numerical results are present for the claimed method. This makes the manuscript impossible to audit and is a load-bearing deficiency.","section":"Full text"},{"comment":"The abstract states that the method establishes 'model-independent limits for rare decays branching fractions of the top quark.' As written, the comparison Γ_t^meas = Γ_SM + Γ_BSM only constrains the total non-SM contribution to the width. If new physics also modifies the dominant t→Wb partial width, then Γ_BSM includes both that modification and any exotic partial width. A positive exotic branching fraction can be compensated by a reduced t→Wb width, leaving Γ_t^meas ≈ Γ_SM. Conversely, an enhanced t→Wb coupling would mimic an exotic excess. The claim of model-independent rare-decay bounds therefore requires the assumption that Γ(t→Wb) is unchanged; this must be stated and justified, or the claim must be weakened to a bound on the total non-SM width contribution.","section":"Abstract"}],"minor_comments":[{"comment":"The abstract does not specify the FCC-ee center-of-mass energy, integrated luminosity, or the expected precision of the total-width extraction. These are necessary for any quantitative statement and would be expected in the body.","section":"Abstract"},{"comment":"The phrase 'model-independent limits for rare decays branching fractions' contains a grammatical redundancy; consider 'model-independent bounds on rare top-quark branching fractions.'","section":"Abstract"}],"recommendation":"reject","confidential_remarks":"The supplied full text is an unrelated paper (apparently arXiv:2508.06960), so the manuscript is not in a reviewable state. I have nonetheless evaluated the abstract. Even with the correct body, the abstract's model-independence claim needs a careful statement of the assumption that the dominant t→Wb partial width is unaffected by new physics; otherwise the proposed bound is a bound on the total BSM width, not specifically on exotic branching fractions. If the authors resubmit the correct manuscript, that issue should be addressed."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Colleague,\n\nTwo things you should know upfront. First, the full text attached to this review is not the paper — it's an unrelated cs.AI benchmark (arXiv:2508.06960). So I can only judge the abstract of 2508.06954, and anything I say about the body is guesswork. Second, the central idea is sound but the abstract's phrasing is too strong.\n\nThe inclusive strategy — measure the total top width in e+e- → ttbar and compare to the SM prediction — is a clean way to bound non-SM decay contributions without knowing the final state. That's a genuinely useful complement to LHC channel-by-channel searches, and it strengthens the FCC-ee physics case. If the body contains a proper simulation with an error budget, it could be a solid reference for the machine's top program.\n\nThe soft spot is the step from 'width excess' to 'limits on rare decay branching fractions.' A measured excess constrains the total non-SM width, not specifically exotic branching fractions. If new physics also changes the dominant t→Wb partial width — say, suppresses it while adding an exotic channel — the two effects can cancel, leaving no excess. The stress-test note is right about this. The paper can fix it by either justifying the assumption that t→Wb is SM or by reframing the result as a bound on the total non-SM width, with branching-fraction limits derived under a stated benchmark. That's a presentational fix, not a fatal flaw, and the body may already address it.\n\nThe abstract alone has no numbers, no detector assumptions, no error budget, so I can't audit soundness or novelty here. The reference list isn't inspectable, so I can't check prior ILC and FCC-ee width-extraction studies. That's not a knock on the authors; it's a limitation of the material I was given.\n\nWho's this for? People working on FCC-ee physics potential and top-quark EFT interpretations. It's a prospective sensitivity projection, not a constraint on today's data, and it should be labeled that way.\n\nRecommendation: send it to peer review. The idea is worth refereeing, and the caveat is fixable. I'd ask the referee to push on the t→Wb assumption and the interpretation of the bound. For a reading group, wait until you can get the actual paper.\n\nBest,\n[You]","headline":"The inclusive top-width excess idea at FCC-ee is useful and should be refereed, but the abstract's 'model-independent branching fraction' claim is too strong without an explicit assumption about the dominant t→Wb width; also the supplied full text is the wrong paper, so no audit is possible.","tokens_in":6106,"tokens_out":2923,"would_cite":false,"duration_ms":30341,"reading_group":"maybe","serious_thinker":"unclear","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":[],"model":"deepseek-v4-flash","headline":"Measuring the total top decay width at FCC-ee can bound any exotic top decay mode, without knowing what the mode is.","keywords":["top quark","exotic decays","total width","FCC-ee","e+e- collisions","model-independent bounds","rare decays","top pair production"],"falsifier":"A concrete check is to extract the top total width from two different final states at FCC-ee, for example leptonic and hadronic top decays. If the two reconstructed widths disagree beyond combined uncertainties, the inclusive width is not a clean production-plus-decay observable, undermining the model-independent bound. A second check: if the measured t tbar cross section at FCC-ee deviates from the standard-model prediction by an amount comparable to the claimed width sensitivity, the normalization assumption behind the method would fail.","tokens_in":1063,"feed_emoji":"⚛️","tokens_out":2382,"duration_ms":62174,"temperature":0.7,"pith_summary":"This paper proposes using direct top-pair production at a future e+e- collider, FCC-ee, to measure the total width of the top quark and compare it to the standard-model prediction. Because any non-standard decay of the top contributes to the total width, an observed excess would be a model-independent signal of new physics, regardless of the exotic final state. The authors argue that the clean FCC-ee environment makes this inclusive measurement feasible, allowing rare top-quark branching fractions to be constrained more directly than in hadronic collisions. If correct, this would establish a new, final-state-agnostic strategy for probing new physics coupled to the top quark.","feed_headline":"FCC-ee width check bounds every exotic top decay","feed_subtitle":"Measure the top's total decay width in clean e+e- collisions; any excess over theory flags new physics.","key_machinery":"The central object is the inclusive top decay width, $\\Gamma_t$, reconstructed from direct $t\\bar t$ production at FCC-ee. Its measured value is compared with the precisely predicted standard-model total width $\\Gamma_{\\mathrm{SM}}$; the difference, $\\Gamma_t - \\Gamma_{\\mathrm{SM}}$, equals the sum of all non-standard partial widths and therefore bounds any individual exotic branching fraction. The method works because it needs no specific decay-mode tag, only an accurate total-width measurement.","core_discovery":"The central claim is that the total top decay width measured in e+e- -> t tbar events at FCC-ee provides an inclusive, model-independent probe of exotic top decays. In the standard model the top width is predicted with good accuracy; any measured excess over that prediction must come from additional, non-standard partial widths. Summing all possible exotic partial widths, the excess directly bounds the branching fraction of any rare top decay, whether or not the decay products are identified. The method exploits the clean lepton-collider environment, where the t tbar production rate and final-state selection are well understood, so that the total width can be extracted without relying on a s","pith_inferences":["The same inclusive-width logic could be transferred to other proposed lepton colliders and to other short-lived particles, such as the Higgs boson, where a total-width measurement can bound exotic and invisible decays without tagging them.","The practical sensitivity will likely be limited by luminosity and beam-energy uncertainties rather than by detector acceptance; a dedicated differential study of t tbar production shapes could separate production systematics from decay-width effects.","A combined analysis of the total width and specific final-state searches would allow the model-independent excess to be decomposed into contributions from multiple exotic modes, sharpening the physics reach beyond a single inclusive limit."],"forward_implications":["Any beyond-standard-model top decay, whatever its final state, contributes to the measured total width, making the total-width check model-independent.","The clean e+e- environment at FCC-ee can resolve a width excess that would be masked by QCD backgrounds and combinatorics at hadron colliders.","A measured excess translates directly into an upper limit on the branching fraction of rare or exotic top decays.","The method also constrains new-physics models that modify the top width through loops or new decay channels, even when no individual exotic final state is searched for."],"supporting_citations":[],"fun_headline_variants":["Top width at FCC-ee sets model-independent exotic bounds","FCC-ee total top width flags any exotic decay excess","Measure top's full width in e+e- to bound exotic decays"],"cache_read_input_tokens":8064,"weakest_assumption_plain":"The argument assumes the t tbar production rate and event selection are essentially insensitive to how the top decays, so any measured width excess is a true signal of new decay modes rather than an artifact of detection efficiency or luminosity error.","fun_headline_variants_meta":{"raw":{"variants":["Top width at FCC-ee sets model-independent exotic bounds","FCC-ee total top width flags any exotic decay excess","Measure top's full width in e+e- to bound exotic decays"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000167,"raw_usage":{"total_tokens":1036,"prompt_tokens":625,"completion_tokens":411,"prompt_tokens_details":{"cached_tokens":256},"prompt_cache_hit_tokens":256,"prompt_cache_miss_tokens":369,"completion_tokens_details":{"reasoning_tokens":355}},"tokens_in":369,"tokens_out":411,"duration_ms":4759,"temperature":1.0,"reasoning_tokens":355,"cache_read_input_tokens":256,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-05T22:24:57.495586+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"A concrete check is to extract the top total width from two different final states at FCC-ee, for example leptonic and hadronic top decays. If the two reconstructed widths disagree beyond combined uncertainties, the inclusive width is not a clean production-plus-decay observable, undermining the model-independent bound. A second check: if the measured t tbar cross section at FCC-ee deviates from the standard-model prediction by an amount comparable to the claimed width sensitivity, the normalization assumption behind the method would fail.","supporting_citations":[],"review_version":1}