{"id":"f618a919-6bf3-4318-ba23-236a39e0aa8c","arxiv_id":"2412.01956","paper_version":1,"verdict":"ACCEPT","confidence":"MODERATE","novelty_score":6.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":4,"one_line_summary":"New bounds from ATLAS 13 TeV di-lepton searches force the malaphoric B3-L2 Z' to exceed 2.8 TeV to preserve its b to s l+ l- fit, and the HL-LHC is expected to reach 4.2 TeV.","lead":"This paper derives new LHC constraints on the malaphoric B3-L2 model, a kinetic-mixing extension of the B3-L2 Z' model proposed for the b to s l+ l- anomalies. Recasting the 139 inverse femtobarn ATLAS di-lepton search, it finds Z' masses below 2.8 TeV are excluded in the region that fits the anomaly data, with the HL-LHC projected to probe up to 4.2 TeV.","discovery_kind":"new_application","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The 2.8 TeV bound inherits the unproven assumption that additional hadronic charm-loop contributions to b→sℓℓ are small; if that assumption fails, the fit region from Ref. [1] shifts and the quoted mass bound does not follow.","rationale":"The paper's own framing makes the conditional nature explicit: 'We shall investigate the case that the additional effective hadronic contributions are small and fit a new physics contribution to the measurements' (Section 1). The quoted lower bound is therefore the intersection of a collider exclusion with a particular new-physics fit region. The reader's weakest-assumption analysis identifies exactly this point. The recasting itself — the kinetic-mixing diagonalization, the approximate mass relations (21)-(24), the ATLAS limit interpolation (25), and the scan protocol for Fig. 4 — is internally consistent, and the ancillary UFO and iterative solver are positive evidence. The only place where the central statement could fail without any internal error is the external fit region. A re-analysis with hadronic nuisance parameters profiled over the ranges estimated in Refs. [2,3,4,5] would settle it. Since the paper transparently states the assumption and does not overclaim a model-independent bound, no verdict change is warranted; the caveat should be retained in the acceptance.","tokens_in":14122,"tokens_out":16890,"duration_ms":145401,"concrete_test":"Re-run the fit of Ref. [1] with the non-local charm-loop hadronic contribution treated as a nuisance parameter profiled over the uncertainty ranges estimated in Refs. [2,3,4,5], instead of fixed to zero, and recompute the R=1 contour of Eq. (26) over the resulting 95% CL region. If the allowed region at MZ′=2.8 TeV disappears or moves above 2.8 TeV, the headline bound is not robust; if it remains, the concern is laid to rest.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The central numerical claim is not an unconditional collider constraint: it is the intersection of the ATLAS di-lepton limit with the 95% CL good-fit region taken from Ref. [1]. Ref. [1]'s region is obtained under the explicit working assumption, stated in Section 1, that 'additional effective hadronic contributions are small', because the largest theory uncertainty in b→sℓ+ℓ− is the non-local charm-loop contribution (Refs. [2,3,4,5]). The paper does not quantify how the fit contour moves if the hadronic nuisance parameters are allowed to float over the ranges discussed in Refs. [2,3,4,5]; it only states that existing estimates are too small to explain the discrepancy. If a future charm-loop estimate shifts the C9/C10 best-fit point by more than the width of the 95% contour, the scanned quantities x=(3 TeV/MX)gX and y=(3 TeV/MX)sinχ in Fig. 4 would move, and the quoted MZ′>2.8 TeV bound would not follow. The HL-LHC projection to 4.2 TeV inherits the same dependence and also assumes naive sqrt(luminosity) scaling of the expected limit, with the caveat to Ref. [21] noted. This is a conditional statement rather than an internal inconsistency, but it is the least secure link in the argument.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"This paper confronts the malaphoric B3-L2 Z' model with the ATLAS 139 fb^-1 13 TeV resonant di-lepton search. The author derives the Z' couplings in the presence of kinetic mixing, gives an approximate analytic solution for the physical masses/couplings valid to O((M_Z/M_Z')^2), and supplies an iterative numerical method for higher precision. Using MadGraph at tree level, the paper computes pp -> Z' -> e+e-/mu+mu- cross sections times branching ratios, interpolates/extrapolates the ATLAS limits using Eq. (25), and overlays the 95% CL fit region from Ref. [1]. The central result is that, within the fit region, the ATLAS search leaves a non-negligible allowed window only for M_Z' > 2.8 TeV, and the paper estimates that the HL-LHC at 3000 fb^-1 will be sensitive to M_Z' = 4.2 TeV.","tokens_in":14443,"tokens_out":8921,"duration_ms":99255,"significance":"If the result holds, it is an important step for the B3-L2 program: the kinetically mixed 'malaphoric' variant, which is currently preferred by global fits to b -> s l+ l- data, is much more strongly constrained by LHC di-lepton searches than the original B3-L2 model, yet a TeV-scale window survives. The paper's strengths are its transparency and reproducibility: the mixing derivation is clean, the validity range of the epsilon expansion is stated, an iterative solution is provided, and the UFO model and numerical code are made available in the ancillary files. The recasting follows a previously validated method. The main caveat is that the 2.8 TeV lower bound is not a pure collider limit but an intersection with the 95% CL fit region of Ref. [1], which is obtained under the explicitly stated assumption that additional effective hadronic contributions to b -> s l+ l- are small. This is a limitation of the interpretation, not an internal inconsistency; the manuscript is honest about it, though the abstract could state it more prominently.","major_comments":[],"minor_comments":[{"comment":"The fit region is attributed to 'Ref. [17]' twice in Section 3 ('As mentioned above, the malaphoric B3-L2 model was fit ... in Ref. [17]' and 'We pick an example point in parameter space from Ref. [17]'), but that fit is from Ref. [1]; Ref. [17] is the earlier di-lepton recasting paper. Please correct the cross-reference.","section":"§3, recasting paragraph"},{"comment":"The sentence 'Figs. 3d and 3d show that MX = 4 TeV and MX = 6 TeV have some allowed parameter space' should read 'Figs. 3c and 3d'.","section":"§3, Fig. 3 discussion"},{"comment":"The abstract states the 2.8 TeV bound without qualification, but the bound applies under the working assumption, made in Section 1, that additional effective hadronic contributions to b -> s l+ l- are small; making that condition explicit in the abstract and conclusion would prevent a too-strong reading of the result.","section":"Abstract and §4"},{"comment":"The 4.2 TeV HL-LHC projection uses naive sqrt(L) scaling even though Ref. [21] argues against that practice; the text should explicitly label the projection as an optimistic sensitivity estimate rather than a guaranteed exclusion.","section":"§3, Eq. (27)"},{"comment":"The extrapolation of Eq. (25) to z>0.1 is mentioned in the text, but Fig. 4's legend entry 'Gamma_Z'/M_Z' > 0.1' does not by itself demarcate where the extrapolated region affects the R=1 contour; please shade or outline that region directly on the plot.","section":"§3, Eq. (25) and Fig. 4"},{"comment":"The sentence 'sin chi is then scanned between the value consistent with y and -0.95' is hard to parse; spell out the scan range explicitly (for example, sin chi in [-0.95, E] with E = y M_X/(3 TeV)) before introducing E in the footnote.","section":"§3, scan description"}],"recommendation":"minor_revision","confidential_remarks":"The manuscript is a competent and honest recasting. The main risk is that the numerical headline depends on the 95% fit region of the author's own prior paper (Ref. [1]), which is not yet published; the editor may wish to confirm that Ref. [1] is available or will be available by the time this paper appears. The manuscript's handling of the hadronic-uncertainty caveat is acceptable, and the inclusion of the UFO model and numerical code is a strength."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Ben's paper is worth a serious look. The new content is the application of the ATLAS di-lepton resonance search to the malaphoric B3-L2 model, and the result is a concrete bound: within the region of parameter space that fits b→s data, the Z' mass is pushed above 2.8 TeV. The coupling derivation is compact, the (MZ/MZ')^2 approximation is stated with its range, and the paper ships the UFO files and a Python solver for the full kinetic-mixing equations. That is exactly the kind of reproducibility that makes a constraint paper useful.\n\nThe LHC recasting itself follows a method the author and others validated earlier, and the paper is properly careful about the width interpolation and the regions where it extrapolates. The HL-LHC projection is labeled an estimate and cites the known caveat about sqrt(L) scaling. That is fine.\n\nThe soft spot is not in the collider calculation; it is upstream. The 2.8 TeV number is the intersection of the ATLAS limit with the 95% good-fit region taken from the author's earlier paper, and that region was obtained under the explicit assumption that additional hadronic contributions to b→sll are small. The paper says so, but it does not quantify how the fit contour moves if that assumption is relaxed. So the mass bound is conditional. If a future charm-loop estimate shifts the C9/C10 best-fit point, the bound would move. The paper does not hide this—the abstract and Section 1 both state the assumption—but a reader who quotes 'MZ'>2.8 TeV' without the caveat will overstate it.\n\nThe minor points: approximating θsb=0 in the cross-sections is justified at one benchmark point, and the conclusion that it holds over the whole parameter space is plausible but not shown in detail. The wide-resonance region z>0.1 is extrapolated and is excluded from the main plots anyway. Fine.\n\nOverall, this is a honest, focused paper. It does not pretend to solve the hadronic uncertainty; it constrains a model under a stated assumption. The work is formally grounded and reproducible. It deserves peer review. I would send it to a competent referee, asking them to check the coupling derivation and to press on a sensitivity statement about the fit region, but I don't see a load-bearing flaw.","headline":"A clean, reproducible LHC constraint on a specific Z' model; the headline mass bound is real but inherits the author's working assumption about hadronic effects in the b→s fit.","tokens_in":15022,"tokens_out":3082,"would_cite":true,"duration_ms":176040,"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 malaphoric $B_3-L_2$ model can still explain the B-meson flavour anomalies only if its $Z^\\prime$ boson is heavier than 2.8 TeV, and the HL-LHC should reach 4.2 TeV.","keywords":["B-anomalies","beyond the Standard Model","bump hunt","kinetic mixing","Z' boson","di-lepton resonance search","lepton flavour universality","LHC"],"falsifier":"If the HL-LHC accumulates 3000 fb$^{-1}$ and finds no resonant di-muon excess above the expected background in the 3 to 4.2 TeV mass window while the $b \\to s l^+ l^-$ anomalies persist, the model's remaining 95% good-fit region would be excluded, since the paper estimates that luminosity is sufficient to reach $M_{Z^\\prime} = 4.2$ TeV.","tokens_in":13849,"feed_emoji":"⚛️","tokens_out":8636,"duration_ms":72316,"temperature":0.7,"pith_summary":"The paper asks whether the malaphoric $B_3-L_2$ model, a proposed explanation of persistent tensions in $b \\to s l^+ l^-$ transitions, can survive direct production searches at the LHC. Because this model's $Z^\\prime$ boson has order-unity kinetic mixing with hypercharge, it couples to valence quarks, making it far easier to produce at a proton collider than the $Z^\\prime$ of the original unmixed model. Recasting the ATLAS 139 fb$^{-1}$ 13 TeV resonant di-lepton search, the paper finds that the entire 95% good-fit region is excluded for $Z^\\prime$ masses below about 2.8 TeV, while a non-negligible allowed region survives at higher masses. The paper estimates that the HL-LHC, with 3000 fb$^{-1}$, would extend sensitivity to $M_{Z^\\prime} = 4.2$ TeV and cover most of the remaining parameter space.","feed_headline":"B-meson anomaly Z-prime must be heavier than 2.8 TeV","feed_subtitle":"Di-lepton searches at 13 TeV rule out lighter Z' bosons; the HL-LHC would test the region up to 4.2 TeV.","key_machinery":"The load-bearing object is the $Z^\\prime$ boson of the malaphoric $B_3-L_2$ model, defined by a spontaneously broken $U(1)_X$ gauge symmetry with charge $X = B_3 - L_2$ and a sizeable kinetic mixing $\\sin \\chi$ between the $X$ gauge boson and hypercharge. The kinetic mixing generates family-universal $Z^\\prime$ couplings to all fermions, so the $Z^\\prime$ acquires first-generation quark couplings and $u\\bar{u} \\to Z^\\prime$ dominates LHC production, making the model directly testable in di-lepton resonance searches. To scan the parameter space, the paper uses the approximate solution of the neutral gauge-boson mixing equations in the limit $M_Z/M_{Z^\\prime} \\ll 1$, namely $M_{Z^\\prime} = \\sqrt{1 + s_w^2 s_\\chi^2}\\, M_X / c_\\chi$, together with relations connecting $M_{Z^\\prime}$, $M_X$, and $\\sin \\chi$; a fixed-point iteration in the appendix refines this to arbitrary precision. The ATLAS bounds are recast through the interpolation $s(z, M_{Z^\\prime}) = s(0, M_{Z^\\prime})\\left(s(0.1, M_{Z^\\prime})/s(0, M_{Z^\\prime})\\right)^{z/10}$ with $z = \\Gamma_{Z^\\prime}/M_{Z^\\prime}$, and the exclusion is taken as the maximum over muon and electron channels of the ratio of predicted $\\sigma \\times \\mathrm{BR}$ to the observed upper limit.","core_discovery":"The central claim is a model-dependent lower bound obtained by overlaying the model's predicted $\\sigma(pp \\to Z^\\prime) \\times \\mathrm{BR}$ on the observed 95% limits of the ATLAS resonant di-lepton search. Within the 95% CL region preferred by the earlier SMEFT fit to $b \\to s l^+ l^-$ observables, electroweak precision data, and LEP2 di-lepton cross sections, the paper finds that at least $M_{Z^\\prime} > 2.8$ TeV is required after the Run II ATLAS search, with the di-muon channel providing the strongest constraint at $M_X = 2$ and $3$ TeV. For $M_X = 4$ and $6$ TeV, a non-negligible allowed region survives. Scaling the expected ATLAS sensitivity by the square root of the luminosity ratio gives an estimated HL-LHC reach of $M_{Z^\\prime} = 4.2$ TeV. If correct, the malaphoric $B_3-L_2$ model remains a viable explanation of the B-anomalies only for $Z^\\prime$ masses above a few TeV, and the HL-LHC can test the remaining region.","pith_inferences":["If the $b \\to s$ anomalies persist and the 2.8 TeV threshold survives, the model makes a sharp testable prediction: a high-mass $Z^\\prime$ should appear in HL-LHC di-muon spectra between roughly 3 and 4.2 TeV, with $\\mathrm{BR}(Z^\\prime \\to \\mu^+\\mu^-) \\approx 0.48$; this consequence is implicit in the paper.","The paper's equivalence between the kinetically mixed malaphoric model and a zero-mixing model with charge $X = B_3 - L_2 + \\alpha Y$ implies that the same mass bound should transfer to ultraviolet completions phrased in terms of a hypercharge-shifted charge assignment.","The $\\sqrt{L}$ luminosity scaling used for the HL-LHC projection is an approximation, and the paper itself cites a caveat about that procedure; a more detailed treatment including systematic uncertainties could shift the 4.2 TeV reach by a few hundred GeV.","The derived mass bound is conditional on the assumption that additional effective hadronic contributions, notably charm-loop rescattering, are small; if refined estimates enlarge those contributions, the fit region would move and the 2.8 TeV statement would need to be re-derived."],"forward_implications":["If the bound stands, the malaphoric $B_3-L_2$ model can only improve the fit to $b \\to s l^+ l^-$ data when $M_{Z^\\prime} > 2.8$ TeV; at $M_X = 2$ and $3$ TeV the whole 95% fit region is already excluded.","The HL-LHC at 3000 fb$^{-1}$ is expected to exclude the remaining good-fit region up to $M_{Z^\\prime} = 4.2$ TeV, covering almost all currently allowed parameter space.","Although the $Z^\\prime$ couples to electrons through kinetic mixing, the di-muon channel drives the exclusions at low $M_X$, consistent with the model's large branching ratio $\\mathrm{BR}(Z^\\prime \\to \\mu^+\\mu^-) \\approx 0.48$.","Since CMS has performed a similar di-lepton search, the paper expects CMS bounds to be very similar to those derived from ATLAS.","In the region relevant to the fit, LHC production is dominated by $u\\bar{u} \\to Z^\\prime$, so the model's LHC signature is a high-mass di-lepton bump rather than the $b$-associated production of the original unmixed model."],"supporting_citations":[{"why":"defines the malaphoric $B_3-L_2$ model and supplies the 95% CL good-fit region in $\\{g_X/M_X, \\sin\\chi/M_X, \\theta_{sb}\\}$ against which the LHC constraints are tested.","marker":"[1]"},{"why":"the ATLAS 139 fb$^{-1}$ 13 TeV resonant di-lepton search whose observed 95% upper bounds on $\\sigma \\times \\mathrm{BR}$ are re-cast in the present paper.","marker":"[16]"},{"why":"provides the re-casting procedure and the interpolation formula (25) that converts ATLAS limits from narrow-width to arbitrary width-to-mass ratio $z$.","marker":"[17]"},{"why":"supplies the neutral gauge-boson mixing relations (10) and (13)-(15) used to convert the input scale $M_X$ and mixing $\\sin\\chi$ into the physical mass $M_{Z^\\prime}$.","marker":"[12]"},{"why":"gives the estimated charm-loop hadronic uncertainty that underlies the paper's assumption that a new physics fit to $b \\to s l^+ l^-$ is meaningful.","marker":"[2]"},{"why":"the LHCb lepton-universality measurement that motivates new physics in $b \\to s e^+ e^-$ as well as $b \\to s \\mu^+\\mu^-$, which the kinetic mixing is designed to produce.","marker":"[10]"},{"why":"MadGraph is used to compute tree-level $pp \\to Z^\\prime$ cross sections and branching ratios entering the predicted $\\sigma \\times \\mathrm{BR}$.","marker":"[19]"}],"fun_headline_variants":["Z' boson in B-anomaly model needs mass above 2.8 TeV","LHC di-lepton searches push B-anomaly Z' to >2.8 TeV","Malaphoric B3-L2 Z' escapes LHC limits above 2.8 TeV","B-anomaly fix survives LHC: Z' must top 2.8 TeV"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The load-bearing premise is that additional non-perturbative hadronic contributions to $b \\to s l^+ l^-$ (notably charm-loop rescattering) are small enough that the new physics fit used to define the good-fit region is meaningful; the paper states it will assume this case and does not prove it.","fun_headline_variants_meta":{"raw":{"variants":["Z' boson in B-anomaly model needs mass above 2.8 TeV","LHC di-lepton searches push B-anomaly Z' to >2.8 TeV","Malaphoric B3-L2 Z' escapes LHC limits above 2.8 TeV","B-anomaly fix survives LHC: Z' must top 2.8 TeV"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000741,"raw_usage":{"total_tokens":3358,"prompt_tokens":1046,"completion_tokens":2312,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":662,"completion_tokens_details":{"reasoning_tokens":2211}},"tokens_in":662,"tokens_out":2312,"duration_ms":13638,"temperature":1.0,"reasoning_tokens":2211,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-11T23:58:59.643573+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"If the HL-LHC accumulates 3000 fb$^{-1}$ and finds no resonant di-muon excess above the expected background in the 3 to 4.2 TeV mass window while the $b \\to s l^+ l^-$ anomalies persist, the model's remaining 95% good-fit region would be excluded, since the paper estimates that luminosity is sufficient to reach $M_{Z^\\prime} = 4.2$ TeV.","supporting_citations":[{"cited_title":"Malaphoric $Z'$ models for $b \\rightarrow s \\ell^+ \\ell^-$ anomalies","cited_arxiv_id":"2409.06804","evidence_quote":"defines the malaphoric $B_3-L_2$ model and supplies the 95% CL good-fit region in $\\{g_X/M_X, \\sin\\chi/M_X, \\theta_{sb}\\}$ against which the LHC constraints are tested."}],"review_version":1}