{"id":"d798e667-580e-4c85-b37c-d87cbad7c1e8","arxiv_id":"2505.13323","paper_version":2,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":4.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":5,"one_line_summary":"In the U1 and S1 leptoquark models, the ratio R_Λ_c* for Λ_b -> Λ_c*(2595,2625) τ ν̄_τ decays deviates from the Standard Model prediction, making it a promising probe of new physics.","lead":"This paper predicts how the decay of a bottom baryon into an excited charmed baryon and a tau lepton changes if leptoquarks exist. It finds the ratio of tau to light-lepton decay rates is more sensitive to these particles than other observables, offering a new way to test current flavor anomalies.","discovery_kind":"extension","skeptic_critique":{"model":"deepseek-v4-flash","headline":"Claimed distinguished R_Λ_c* deviation is never quantified against SM uncertainty; the ~13% shift from CVL≈0.065 may lie within the combined form-factor and coupling error budget, so the central sensitivity claim is not yet demonstrated.","rationale":"The reader's verdict is CONDITIONAL, with the weakest assumption identified as the reliability of the lattice form factors from [82,83] and their covariance matrices. My stress-test converges on a closely related but sharper concern: even granting those form factors, the paper never quantifies whether the predicted R_Λ_c* deviation is statistically distinguishable from the SM prediction. The dominant NP effect is a small CVL≈0.065, corresponding to roughly a 13% shift in the ratio; without propagating the fitted-coupling uncertainties and the form-factor covariance into a significance statement, the 'distinguished divergence' asserted in Secs. III-IV could be within the SM uncertainty band. This is not an accusation of error; it is a request for the numeric output that the reader already noted is missing. The known lattice-vs-HQET tension for these transitions further strengthens the need for a form-factor cross-check. Since the reader's CONDITIONAL verdict already requires numeric predictions and comparison with [95], my concern does not change the verdict; it sharpens the condition: report R_Λ_c* values with uncertainties and a significance test, and test sensitivity to the hadronic input. Thus UNCHANGED is appropriate, with agreement 'partial' because my emphasis is on the significance test rather than on form-factor correctness per se.","tokens_in":28674,"tokens_out":8288,"duration_ms":86159,"concrete_test":"Compute R_Λ_c*(q²) for SM, U1, and S1 using the Table I central values and full covariance matrices, and propagate the 1σ uncertainties of the best-fit LQ couplings from Fig. 2. Evaluate the bin-by-bin pull (χ²(SM) − χ²(LQ)) for LHCb-like pseudodata with the Run-3/Run-6 sensitivities projected in Ref. [79], and report for which q² bins the NP hypothesis is preferred at ≥1σ. As a robustness cross-check, rerun the same calculation using the HQET form factors of Ref. [92]; if the distinguished divergence disappears or changes sign, the claim is form-factor-dependent.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The headline claim that R_Λ_c* is 'particularly sensitive' to U1/S1 leptoquarks rests on the size of the NP shift relative to the SM prediction. From the fit, the dominant NP effect is CVL ≈ 0.065, giving a mostly multiplicative enhancement |1+CVL|^2 ≈ 1.13 of the tau-mode rate relative to the mu-mode denominator. The paper shows only central curves and 1σ form-factor bands (Figs. 3-4); it does not give numeric R_Λ_c* values, their uncertainties, or the statistical significance of the SM-vs-LQ separation. Because the SM and NP predictions share the same lattice form factors, uncertainties partially cancel, but the residual cancellation is incomplete and must be computed with the full covariance matrix plus the 1σ uncertainties of the fitted couplings from Fig. 2. Without such a computation, a ~13% central shift could be compatible with the SM band once form-factor and fit errors are propagated. In addition, the lattice form factors of [83] are the sole hadronic input and are in known tension with HQET-based extractions [91,92]; if the true form factors differ, the predicted deviation could shrink, grow, or move in q². Thus the central claim is not falsifiable from the preprint as written; it needs a quantitative significance test and a cross-check with alternative form-factor input.","agreement_with_reader":"partial"},"referee_report":{"model":"deepseek-v4-flash","summary":"The manuscript studies the semileptonic decays Λ_b → Λ_c*(2595,2625) τ^- ν̄_τ in the Standard Model and in two leptoquark scenarios, the vector U_1 and the scalar S_1. The authors derive the effective Hamiltonian, match the U_1 and S_1 Wilson coefficients to b→cτν, give explicit helicity amplitudes for the 1/2^+ → 1/2^- and 1/2^+ → 3/2^- transitions, and construct the q^2-dependent observables: differential decay rate, LFU ratio R_Λ_c*, forward-backward asymmetry, flat term, and τ longitudinal polarization. Using lattice QCD form factors from Refs. [82,83], they fit the LQ couplings to the current R_D, R_D*, R_J/ψ, F_L^{D*}, P_τ^{D*} data and the B_c→τν bound, and then show q^2 spectra of the Λ_b → Λ_c* observables. The headline finding is that R_Λ_c* is particularly sensitive to the U_1 and S_1 leptoquarks, exhibiting a 'distinguished divergence' from the SM prediction.","tokens_in":28979,"tokens_out":6018,"duration_ms":62226,"significance":"If the sensitivity claim is quantitatively established, the paper would be a useful model-dependent addition to the phenomenology of semileptonic Λ_b decays. The helicity formalism is standard and the explicit expressions for the 1/2^+ → 1/2^- and 1/2^+ → 3/2^- amplitudes with all four-fermion structures are a useful reference. A clear strength is that the LQ couplings are fitted to mesonic observables only, so the Λ_b → Λ_c* predictions are independent consequences of the model rather than a refit of the target modes. The use of the lattice covariance matrices is also to be credited. However, the central claim is currently supported only by visual separation of bands in Figs. 3 and 4: no numerical R_Λ_c* values, uncertainties, or significance estimates are provided, and the entire analysis rests on a single lattice form-factor set that the manuscript itself notes is in tension with HQET-based extractions. These shortcomings prevent the paper from demonstrating the headline sensitivity at the quantitative level required for a journal publication.","major_comments":[{"comment":"The central claim that R_Λ_c* shows a 'distinguished divergence' is inferred from the visual separation of the SM and LQ bands, but the paper provides no numeric predictions, no binned R_Λ_c* values, and no significance estimate. With the best-fit vector coefficient C_VL ≈ 0.065, the dominant effect is roughly a multiplicative |1+C_VL|^2 ≈ 1.13 enhancement, and whether this is distinguishable from the SM depends on the full form-factor covariance and on the 1σ spread of the fitted couplings from Fig. 2, which are not propagated into the displayed bands. I request a quantitative statement, for example a table of binned R_Λ_c* values with form-factor and fit uncertainties, and the SM-vs-LQ separation expressed in units of σ.","section":"Sec. III, Figs. 3 and 4, and Sec. IV"},{"comment":"The numerical analysis uses exclusively the lattice QCD form factors of Refs. [82,83]. The manuscript itself cites Refs. [91,92], which report tensions between these lattice results and HQET-based determinations of the same form factors. Since the claimed NP shift in R_Λ_c* is only of order 10%, an alternative form-factor input could change the size, the sign, or the q^2 location of the deviation. A cross-check with HQET-based form factors, or at least a quantitative study of the sensitivity of the predicted R_Λ_c* deviation to the form-factor parameterization, is needed before the headline claim is robust.","section":"Secs. II.D and III"},{"comment":"There is an internal inconsistency in Table I: the rows after h(3/2^-)_+ are labeled h(1/2^-)_⊥ = 1.23(15) and h(1/2^-)_⊥' = -0.02133(95), but the same values appear to belong to the 3/2^- transition (h(3/2^-)_⊥ and h(3/2^-)_⊥'), while the 1/2^- h_⊥ entry was already listed above as 0.91(23). Because the mislabeled quantities enter the F_V4, F_A4 and tensor helicity amplitudes used for Λ_c(2625), this affects the numerical results for the 3/2^- channel. The table labels should be corrected and the numerics rechecked.","section":"Table I"}],"minor_comments":[{"comment":"The abstract states that the distinguished divergence appears in the high-q^2 region, but Sec. III reports that R_Λ_c*(2595) deviates near the lower end of the q^2 spectrum while R_Λ_c*(2625) deviates at higher q^2; these statements should be reconciled.","section":"Abstract and Sec. III"},{"comment":"The sentence 'we used a 1σ bound from the current experimental data of R_D(∗), R_J/ψ, F_L^{D*}, P_τ^{D*}' is imprecise: the analysis uses a χ^2 fit with the full experimental covariance, not a simple 1σ bound. The wording should be corrected.","section":"Sec. IV"},{"comment":"The definition of dO_i in Eq. (35) gives the discrepancy from experiment in units of σ_exp, but the entries in Table V are hard to read and the sign convention (positive/negative superscripts) is not explained. Please clarify the presentation.","section":"Eq. (35) and Table V"},{"comment":"There are minor language issues, including 'the the U_1 and S_1 leptoquark frameworks' and 'provide complimentary probe'; these should be fixed in a final proofread.","section":"Sec. IV"}],"recommendation":"major_revision","confidential_remarks":"The manuscript is within the scope of the journal and I found no obvious novelty or attribution problems. The main risk is that the headline sensitivity claim is not yet quantitatively demonstrated; the requested additions (numerical values, significance estimates, and a form-factor cross-check) are feasible within the scope of the paper, so I did not recommend rejection."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Two things to know. First, this is a competent and useful extension of the EFT analysis of Λ_b→Λ_c*(2595,2625)τν decays to the U1 and S1 leptoquark models. The genuinely new content is the explicit helicity amplitudes for all four-fermion operators, including the tensor amplitudes for both the 1/2+→1/2− and 1/2+→3/2− transitions, and the model-specific predictions for R_Λ_c*. Second, the paper's key claim—that R_Λ_c* is particularly sensitive to these LQs—is not actually demonstrated. The shift is about 13% from |1+C_VL|^2 with C_VL≈0.065, and the paper gives only bands in figures, no numeric R values, no significance, and no propagation of the fit uncertainties on the couplings. The stress-test concern lands.\n\nWhat the paper does well: the helicity formalism is standard and the amplitudes are written out carefully; the fit uses only mesonic inputs (R_D, R_D*, R_J/ψ, F_L^{D*}, P_τ^{D*}, B_c→τν), so the prediction for the baryonic ratio is independent of the target observable. The authors restrict to high q² where the lattice form factors are most reliable, and they are honest about limitations: complex S1 is excluded by LHC bounds, and U1 versus S1 cannot be distinguished in these decays. That is the right behaviour.\n\nThe main soft spot is the absence of quantitative output. Figures 3 and 4 show central curves and form-factor bands, but the reader cannot tell whether the SM-LQ separation is statistically significant. The two predictions share the same lattice form factors, so those uncertainties partially cancel; the residual should be computed with the full covariance matrix and the coupling uncertainties from the χ² fit. A table with R_Λ_c* values and errors, plus a p-value for the separation, would settle the claim. The paper also does not quantitatively compare with the EFT study of Du et al. [95], which is the direct benchmark; stating that they differ by being model-dependent is fine, but a numerical comparison would make the added value clear. The omission of complex-coupling plots is a minor issue since the authors explain why the results are similar.\n\nFor readers working on b→cτν anomalies or LQ models, this is a useful reference. I would send it to a referee but with the request to add numeric predictions and a significance test. No critical flaw; it is a solid, honest calculation that needs finishing.","headline":"Solid but incremental LQ analysis of Λ_b→Λ_c* τν decays; the claimed R_Λ_c* sensitivity is plausible but not quantified, so the paper needs a significance calculation before the headline claim is credible.","tokens_in":29615,"tokens_out":2834,"would_cite":false,"duration_ms":28489,"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":"The lepton-flavor-universality ratio $R_{\\Lambda_c^*}$ in $\\Lambda_b\\to\\Lambda_c^*(2595,2625)\\tau\\bar{\\nu}_\\tau$ decays is particularly sensitive to U1 and S1 leptoquarks, showing a clear departure from the standard-model prediction in…","keywords":["leptoquarks","lepton flavor universality","Lambda_b decays","excited charmed baryons","helicity amplitudes","b to c tau nu transitions","lattice QCD form factors","R_Lambda_c*"],"falsifier":"Measure $R_{\\Lambda_c^*}$ for $\\Lambda_c^*(2595)$ and $\\Lambda_c^*(2625)$ in narrow $q^2$ bins near zero recoil in a high-statistics experiment; if the measured ratios track the standard-model prediction bin by bin while $R_D$ and $R_{D^*}$ remain elevated, the leptoquark interpretation of the claimed shift would be excluded.","tokens_in":28416,"feed_emoji":"⚛️","tokens_out":9917,"duration_ms":84417,"temperature":0.7,"pith_summary":"This paper asks whether decays of the bottom baryon $\\Lambda_b$ into the excited charmed baryons $\\Lambda_c^*(2595)$ and $\\Lambda_c^*(2625)$ with a $\\tau$ lepton can reveal new physics that meson decays hide. It takes the U1 vector and S1 scalar leptoquark models, constrains their couplings with current $b\\to c\\ell\\nu$ data, and computes the full $q^2$ dependence of the decay observables using lattice QCD form factors and explicit helicity amplitudes. The central result is that the lepton-flavor-universality ratio $R_{\\Lambda_c^*}$ is especially sensitive to both leptoquarks and departs from the standard-model prediction in the allowed kinematic region, while angular observables and the $\\tau$ polarization remain close to the standard model. The paper concludes that measuring $R_{\\Lambda_c^*}$ provides a complementary, relatively unexplored test of the anomalies in $b\\to c\\tau\\nu$ transitions.","feed_headline":"Tau decay ratio in excited Lambda_b channels flags leptoquarks","feed_subtitle":"Both U1 and S1 leptoquarks push R_Lambda_c* away from the standard model, giving a new lepton-flavor test.","key_machinery":"The machinery is the helicity-amplitude decomposition of the $1/2^+\\to 1/2^-$ and $1/2^+\\to 3/2^-$ transitions for vector, axial-vector, scalar, pseudoscalar, and tensor operators, with Wilson coefficients obtained from the U1 and S1 leptoquark Lagrangians through Fierz transformations and evolved to the $m_b$ scale. The hadronic input is the set of lattice QCD form factors and covariance matrices for $\\Lambda_b\\to\\Lambda_c^*(2595,2625)$; the analytical work is the explicit construction of the helicity amplitudes, the differential decay rate, and the $q^2$-dependent observables. The controlling mechanism is the factor $|1+C_{V_L}|^2$, which dominates the rate, cancels in normalized angular distributions, and leaves $R_{\\Lambda_c^*}$ as the clear new-physics probe.","core_discovery":"The paper claims that for both final states, the ratio $R_{\\Lambda_c^*}=\\mathcal{B}(\\Lambda_b\\to\\Lambda_c^*\\tau\\bar{\\nu}_\\tau)/\\mathcal{B}(\\Lambda_b\\to\\Lambda_c^*\\ell\\bar{\\nu}_\\ell)$ receives visible upward shifts when a U1 vector or S1 scalar leptoquark at a benchmark mass of 2 TeV is added to the standard model, after fitting the leptoquark couplings to $R_{D^{(*)}}$, $R_{J/\\psi}$, $F_L^{D^*}$, $P_\\tau^{D^*}$, and the $B_c\\to\\tau\\nu$ bound. The deviations appear because vector new physics enters the decay rate through $|1+C_{V_L}|^2$ and survives in the ratio, while scalar and tensor contributions are suppressed near zero recoil by $m_\\tau^2/q^2$. The same structure makes the forward-backward asymmetry, the flat term, and the longitudinal $\\tau$ polarization nearly insensitive to the leptoquarks, singling out the LFU ratio as the observable to measure.","pith_inferences":["If the predicted deviation is confirmed, it would show that vector new physics in $b\\to c\\tau\\nu$ is not an artifact of mesonic form-factor modeling, because baryonic and mesonic transitions carry different hadronic uncertainties.","Because scalar and tensor effects are suppressed by $m_\\tau^2/q^2$ near zero recoil, comparing a high-$q^2$ measurement of $R_{\\Lambda_c^*}$ with one extended to lower $q^2$ could in principle separate the vector Wilson coefficient $C_{V_L}$ from scalar operators.","The excited baryons decay through $\\Lambda_c\\pi\\pi$ final states, so a high-luminosity analysis built around that decay chain could turn $R_{\\Lambda_c^*}$ into a practical observable even though the individual branching fractions are small.","The near-degeneracy of the U1 and S1 predictions suggests that an additional observable, such as the $\\tau$ polarization combined with $R_{\\Lambda_c^*}$, would be needed to break the degeneracy between scalar and vector leptoquark explanations."],"forward_implications":["A measurement of $R_{\\Lambda_c^*}$ in either excited charmed channel supplies a new lepton-flavor-universality test in the tauonic $b\\to c$ sector, complementing the mesonic ratios $R_D$ and $R_{D^*}$.","The LFU ratio is the discriminating observable: the forward-backward asymmetry, flat term, and $\\tau$ polarization overlap with the standard-model predictions, so those observables cannot serve as clean new-physics signals here.","Both U1 and S1 leptoquark scenarios produce similar $R_{\\Lambda_c^*}$ predictions in the studied kinematic region, so observing a deviation would indicate leptoquark-like new physics but would not by itself identify which leptoquark is responsible.","Complex leptoquark couplings leave the predicted observables essentially unchanged near zero recoil, making the conclusions insensitive to unknown CP-violating phases in the fitted couplings.","The high-$q^2$ region, where the lattice form factors are most reliable, is where the claimed deviation is most visible; measurements binned there would be the most informative."],"supporting_citations":[{"why":"Supplies the improved lattice QCD form factors and covariance matrices that drive the numerical predictions.","marker":"[83]"},{"why":"Provides the earlier lattice QCD form factors for $\\Lambda_b\\to\\Lambda_c^*(2595,2625)$ that define the hadronic matrix elements.","marker":"[82]"},{"why":"Defines the U1 and S1 leptoquark Lagrangians and the Fierz relations giving the Wilson coefficients for $b\\to c\\tau\\nu$.","marker":"[28]"},{"why":"Shows that a single U1 leptoquark can simultaneously address the $R_{D^{(*)}}$ and $R_{K^{(*)}}$ anomalies, motivating the scenarios studied here.","marker":"[47]"},{"why":"Provides the current global-fit observables, collider bounds, and Wilson-coefficient expressions used in the $\\chi^2$ fit.","marker":"[10]"},{"why":"Contains the earlier effective-theory study of these decays with a different tensor formalism, the main comparison point for this analysis.","marker":"[95]"},{"why":"Supplies the upper bound on $B_c\\to\\tau\\nu$ used to constrain the leptoquark parameter space.","marker":"[103]"},{"why":"Provides the lattice-QCD uncertainty propagation procedure adopted for combining statistical and systematic form-factor uncertainties.","marker":"[55]"}],"fun_headline_variants":["Leptoquarks shift baryonic tau decay ratio","R_Lambda_c*: new probe for leptoquarks","Excited Lambda_b decays test leptoquark models","U1 and S1 leptoquarks alter Lambda_c* tau ratio"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The lattice QCD form factors for the two excited charmed baryons, including their covariance matrices, correctly describe all hadronic matrix elements in the high-$q^2$ region where the analysis is restricted; if those form factors are inaccurate, the predicted deviations in $R_{\\Lambda_c^*}$ could disappear.","fun_headline_variants_meta":{"raw":{"variants":["Leptoquarks shift baryonic tau decay ratio","R_Lambda_c*: new probe for leptoquarks","Excited Lambda_b decays test leptoquark models","U1 and S1 leptoquarks alter Lambda_c* tau ratio"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.00061,"raw_usage":{"total_tokens":2892,"prompt_tokens":1048,"completion_tokens":1844,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":664,"completion_tokens_details":{"reasoning_tokens":1775}},"tokens_in":664,"tokens_out":1844,"duration_ms":14398,"temperature":1.0,"reasoning_tokens":1775,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-15T20:15:40.503242+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Measure $R_{\\Lambda_c^*}$ for $\\Lambda_c^*(2595)$ and $\\Lambda_c^*(2625)$ in narrow $q^2$ bins near zero recoil in a high-statistics experiment; if the measured ratios track the standard-model prediction bin by bin while $R_D$ and $R_{D^*}$ remain elevated, the leptoquark interpretation of the claimed shift would be excluded.","supporting_citations":[],"review_version":1}