{"id":"3593becf-e67b-479e-8e24-2f6ea34297de","arxiv_id":"2501.00610","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":4.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":2,"one_line_summary":"Using public ATLAS dilepton data, the B-L Z' is excluded below 4-6 TeV for g_BL=0.1-0.5, with limits relaxing when invisible decays are allowed and extending to about 7.5 TeV at HL-LHC.","lead":"This paper recasts ATLAS's 13 TeV dilepton search to set lower mass limits on the Z' boson of the B-L extension of the Standard Model. It reports that the LHC now excludes Z' masses up to 4-6 TeV for typical couplings, surpassing the old LEP bounds, and projects HL-LHC reach up to 7.5 TeV.","discovery_kind":"extension","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The invisible-decay rescaling uses the narrow-width approximation, but at g_BL=0.5 and BR_inv=0.9 the resulting Z' width is ~33% of the mass, invalidating the ATLAS narrow-resonance limit used to quote M_Z'>4.8 TeV.","rationale":"The reader's weakest-assumption concern about acceptance, PDF, and K-factor uncertainties is legitimate and would shift the mass limits by hundreds of GeV, but the narrow-width inconsistency is more load-bearing because it invalidates the numerical central claim for the invisible-decay scenario, not just its error bars. The base-model bounds (Fig. 5) and the qualitative LHC-over-LEP conclusion remain credible and follow standard recasting practice; the advertised g_BL=0.5, BR_inv=0.9 bound, however, rests on a resonance width that is far outside the ATLAS narrow-resonance search assumption. A corrected paper should either restrict the invisible-decay analysis to Gamma/M values where the narrow-width approximation is valid or perform a proper broad-resonance recast with appropriate signal templates and interference. The conditional verdict is therefore retained: the paper's message is worth publishing, but the invisible-decay limits, especially the HL-LHC projections in Table III, must be rederived or explicitly qualified.","tokens_in":9242,"tokens_out":12524,"duration_ms":134477,"concrete_test":"Compute Gamma/M = 5 g_BL^2/[12*pi*(1-BR_inv)] for every entry in Tables II-III and Fig. 7; benchmarks with Gamma/M > 0.05 are outside the narrow-resonance regime. Then perform a dedicated recast of the ATLAS 139 fb^-1 search for one representative point, e.g. (g_BL=0.5, BR_inv=0.9, M_Z'=4.8 TeV): generate pp -> Z' -> l+l- with the full width in MadGraph, apply the ATLAS electron/muon selection, and compare the expected dilepton yield against the published background-only limits. If the broad line shape is not excluded, the advertised bound is refuted; if it is excluded, the resulting mass limit will show how much the quoted 4.8 TeV shifts.","verdict_should_be":"CONDITIONAL","load_bearing_attack":"The paper's advertised invisible-decay bounds rely on the narrow-width rescaling in Eq. (3), but the widths that result are not narrow. In the B-L model the visible width is Gamma_vis/M = 5 g_BL^2/(12*pi), obtained by summing N_c Q^2 over SM fermions (three charged leptons with Q=-1 give 3; six quarks with Q=1/3 and N_c=3 give 2). For g_BL=0.5 this is ~3.3%; imposing BR_inv=0.9 multiplies the total width by ten, giving Gamma/M ~ 33% (Gamma ~ 1.6 TeV at M=4.8 TeV). The quoted bound M_Z'>4.8 TeV for g_BL=0.5 and BR_inv=0.9 is therefore obtained by comparing a broad resonance to ATLAS's narrow-resonance observed limit, which is not valid. The problem worsens in Table III: g_BL=0.6 and BR_inv=0.9 gives Gamma/M ~ 48%, and g_BL=0.3 with BR_inv=0.9 gives ~12%. The qualitative statement that invisible decays weaken dilepton limits survives, but the specific mass limits for large BR_inv, and the corresponding HL-LHC projections, are not supported by the presented calculation.","agreement_with_reader":"partial"},"referee_report":{"model":"deepseek-v4-flash","summary":"This paper recasts the ATLAS 139 fb^-1 high-mass dilepton resonance search to constrain the Z' boson of the minimal U(1)_{B-L} model. The authors compute sigma(pp -> Z') x BR(Z' -> ll) at leading order with MadGraph for benchmark gauge couplings and compare it with the ATLAS observed limit line, obtaining M_Z' > 4 TeV for g_BL = 0.1 and M_Z' > 6 TeV for g_BL = 0.5 in the absence of invisible decays. They then model invisible decays by rescaling the dilepton branching ratio with a factor (1 - BR_inv), obtaining relaxed bounds such as M_Z' > 4.8 TeV for g_BL = 0.5 and BR_inv = 0.9, and they use the 'collider reach' code to project HL-LHC sensitivities. The central message is that the LHC now excludes the B-L Z' more strongly than the classic LEP bound M_Z'/g_BL > 7 TeV.","tokens_in":9513,"tokens_out":8246,"duration_ms":82736,"significance":"If the calculation were fully valid, the paper would provide a useful, up-to-date recasting of public LHC data for a well-motivated B-L benchmark, and the HL-LHC projections would help plan future searches. A notable strength is that the bounds are obtained by comparing predictions to an external ATLAS observed limit, with no quantity fitted to the target result. However, the advertised invisible-decay mass limits rely on the narrow-width approximation in regimes where the Z' width is a large fraction of its mass, so the specific numerical claims in Section V and Table III are not supported by the calculation as presented. The qualitative conclusion that the LHC surpasses the LEP bound is robust and would survive the needed corrections; the quantitative limits need revision and uncertainty estimates.","major_comments":[{"comment":"The invisible-decay rescaling of Eq. (3) is presented under the narrow-width approximation, but the benchmarks used for the advertised limits are not narrow. In the B-L model, summing over SM fermions gives Gamma_vis/M = 5 g_BL^2/(12 pi), so for g_BL = 0.5 and BR_inv = 0.9 the total width satisfies Gamma/M = 0.33, and for g_BL = 0.6 with BR_inv = 0.9 it reaches 0.48; even g_BL = 0.3 with BR_inv = 0.9 gives roughly 12%. The quoted bound M_Z' > 4.8 TeV for g_BL = 0.5 and BR_inv = 0.9 is obtained by comparing this broad resonance to the ATLAS narrow-resonance observed limit, so that specific bound and the corresponding Table III HL-LHC entries with large BR_inv are not supported by the calculation as presented. The authors should either restrict BR_inv so that Gamma/M remains small, or replace the narrow-limit comparison with a full Breit-Wigner line shape convolved with the detector mass resolution, and report Gamma/M for every benchmark.","section":"Section V, Eq. (3), and Table III"},{"comment":"The analysis compares leading-order MadGraph predictions for sigma(pp -> Z') x BR(Z' -> ll) directly with the ATLAS observed limit line and treats that line as a universal bound on any narrow spin-1 resonance. This assumes identical acceptance and efficiency to the SSM Z' used by ATLAS, neglects interference with Standard Model Drell-Yan, and assigns no PDF, scale, or NLO K-factor uncertainty. Because the predicted cross sections fall steeply with mass, a 20-30% shift in the signal normalization would move the quoted mass limits by hundreds of GeV. The qualitative finding that LHC bounds exceed the LEP bound is robust, but the precision of the quoted numbers (e.g., M_Z' > 6 TeV for g_BL = 0.5 and the four-digit entries in Tables II and III) is not justified. Please quantify these uncertainties or quote the limits with explicit caveats and rounding.","section":"Section III, Figs. 3-7"}],"minor_comments":[{"comment":"The text contains a direct contradiction: it first says that assuming M_NR < M_Z'/2 would 'not yield meaningful changes' and then says the addition of three light right-handed neutrinos 'will bring meaningful changes to the branching ratio into charged leptons.' With three light right-handed neutrinos of B-L charge -1, the total Z' width increases from a coefficient of 5 to 8, changing BR(Z' -> ll) from 3/5 to 3/8; this is a meaningful change and should be stated consistently.","section":"Section II, right-handed neutrino paragraph"},{"comment":"The sentence 'HL-LHC can reach masses above 6 TeV even BR_inv = 0.9' is contradicted by Table III, whose g_BL = 0.2, BR_inv = 0.9 row gives M_Z' > 5512 GeV. Please rephrase the summary to reflect the coupling dependence shown in the table.","section":"Section VI"},{"comment":"There are multiple typos and grammar errors, including 'codded' for 'coded', 'enforcers' for 'enforces', 'In order words' for 'In other words', 'CTL8NNLO' for what is presumably 'CT18NNLO', and 'will operate with at sqrt(s) = 14 TeV' in the abstract. A careful proofreading pass is needed.","section":"Throughout"},{"comment":"The 'Extrapolation' label in Figure 7 is never explained in the text; the reader cannot tell which portion of the excluded region is extrapolated and on what basis. Please define this in the caption or text.","section":"Figure 7"},{"comment":"No validation details or grid spacing are given for the scanning algorithm used to produce the exclusion curves. Providing a benchmark table or releasing the MadGraph grid/code would improve reproducibility.","section":"Section III"}],"recommendation":"major_revision","confidential_remarks":null},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Two things to know. The base-model result—LHC dilepton data excludes M_Z' > 4 TeV at g_BL = 0.1 and > 6 TeV at g_BL = 0.5, beating LEP—is robust and worth having in one place. The invisible-decay results, which are the paper's headline, rest on an invalid narrow-width approximation. That is the main thing.\n\nWhat is good: this is a clean, standard recast. The authors implement the B-L model, compare with the ATLAS 139 fb^-1 dilepton limit, and produce clear exclusion plots. The LHC-versus-LEP comparison is honest, and the base-model limits are consistent with earlier literature (refs [17-20]). For the base model the width is small enough that the narrow-resonance limit is acceptable. The paper is also well-organized; the Z2 dark matter charge is cosmetic but harmless.\n\nThe soft spot is the invisible-decay section. Eq. (3) uses the narrow-width approximation to rescale the signal by (1 - BR_inv). But the width is not narrow. In the B-L model, Gamma_vis/M = 5 g_BL^2/(12 pi), so at g_BL = 0.5 that is about 3.3%; imposing BR_inv = 0.9 multiplies the total width by ten, giving Gamma/M ~ 33%. The ATLAS observed limit used in Fig. 6 is for a narrow resonance; a resonance with a 33% width would have a different line shape and the cross-section limit is not the same. The same problem affects Table III: g_BL = 0.6 with BR_inv = 0.9 gives ~48%, and even g_BL = 0.3 with BR_inv = 0.9 gives ~12%. So the specific limits like M_Z' > 4.8 TeV for g_BL = 0.5, BR_inv = 0.9 are not supported by the presented calculation. The qualitative statement that invisible decays weaken the bounds survives, but the numbers do not.\n\nTwo smaller issues. First, no digitized limit curve or grid is provided, so the quoted boundaries are hard to verify exactly. Second, no PDF, scale, or K-factor uncertainties are attached; a 20-30% shift would move the mass limits by hundreds of GeV, though the qualitative conclusion survives. There is also a small internal contradiction in Section II about whether light right-handed neutrinos would change the charged-lepton branching ratio.\n\nWho is this for: phenomenologists working on B-L models or Z' searches who want an up-to-date constraint table. The base-model part is a useful summary. The invisible-decay part, as written, should not be used until fixed.\n\nMy recommendation: send it to peer review, but with a note for the referee to check the narrow-width validity. The authors will need to restrict their BR_inv claims to regions where Gamma/M is safely below a few percent, or else redo the limits with a proper broad-resonance interpretation. If that is done, the paper is a modest but legitimate contribution.","headline":"The base-model Z' bounds are solid and worth quoting, but the invisible-decay headline numbers rely on a narrow-width approximation that breaks down at large g_BL and BR_inv.","tokens_in":10119,"tokens_out":5519,"would_cite":false,"duration_ms":53872,"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 ATLAS 139 fb$^{-1}$ dilepton search excludes $B-L$ $Z'$ bosons below 6 TeV for $g_{BL}=0.5$, and even with 90% invisible decays the LHC bound remains stronger than LEP.","keywords":["B-L model","Z' gauge boson","dilepton resonance search","LHC Run 2","invisible decays","HL-LHC projection","LEP bound","narrow-width approximation"],"falsifier":"Recompute the exclusion using the ATLAS binned dilepton likelihood with interference between the $B-L$ $Z'$ and Standard Model Drell-Yan included; if the predicted dilepton yield drops by 20--30%, the mass limits quoted here would move downward by hundreds of GeV.","tokens_in":9029,"feed_emoji":"⚛️","tokens_out":7144,"duration_ms":61709,"temperature":0.7,"pith_summary":"This paper updates the lower mass limit on the $Z'$ gauge boson of the $U(1)_{B-L}$ extension of the Standard Model using the 139 fb$^{-1}$ ATLAS dilepton resonance search. In the minimal model, where the $Z'$ decays only into Standard Model fermions, the authors find $M_{Z'} > 4$ TeV for $g_{BL}=0.1$ and $M_{Z'} > 6$ TeV for $g_{BL}=0.5$. Allowing an invisible branching ratio of $BR_{inv}=0.9$ relaxes the $g_{BL}=0.5$ limit to $M_{Z'} > 4.8$ TeV, but even then the LHC constraint is stronger than the classic LEP bound $M_{Z'}/g_{BL} > 7$ TeV. This matters because $B-L$ models are a simple route to neutrino masses and dark matter, and these limits define how much of that territory remains open.","feed_headline":"ATLAS data rule out B-L Z' bosons below 6 TeV at g_BL=0.5","feed_subtitle":"The 139 fb^-1 dilepton search beats the old LEP bound even when 90% of Z' decays are invisible.","key_machinery":"The central object is the $Z'$ gauge boson of $U(1)_{B-L}$, produced through quark-antiquark annihilation and observed via $Z'\\to \\ell\\ell$. The exclusion mechanism is a grid scan that compares leading-order MadGraph predictions for $\\sigma(pp\\to Z')\\times BR(Z'\\to \\ell\\ell)$ with the ATLAS observed 95% C.L. limit curve, excluding any point whose predicted yield lies above the data. Invisible decays are parametrized in the narrow-width approximation by multiplying the dilepton branching ratio by $(1-BR_{inv})$, which reduces the signal size linearly as $BR_{inv}$ grows.","core_discovery":"The central claim is that the ATLAS Run 2 search for high-mass dielectron and dimuon resonances, interpreted with leading-order simulations of the $B-L$ $Z'$, excludes $Z'$ masses below roughly 4 TeV for $g_{BL}=0.1$ and below 6 TeV for $g_{BL}=0.5$ in the visible-only scenario. When invisible decays are switched on by rescaling the dilepton branching ratio by $(1-BR_{inv})$, the limits weaken monotonically; for $BR_{inv}=0.9$ and $g_{BL}=0.5$ the bound drops to 4.8 TeV. Across the parameter plane, the derived exclusions exceed the longstanding LEP constraint $M_{Z'}/g_{BL} > 7$ TeV, so the LHC has become the strongest collider probe of $B-L$ symmetry. The same analysis projects that the HL-LHC at 14 TeV with $3$ ab$^{-1}$ will exclude $Z'$ masses up to about 7.6 TeV.","pith_inferences":["Beyond the paper, the same rescaling technique could be applied to other narrow $Z'$ models with different quark and lepton couplings, producing a model-independent bound map from the same ATLAS curve.","Beyond the paper, if the $Z'$ carries the dark matter interaction, these limits push invisible-sector benchmarks above roughly 5 TeV for $g_{BL}=0.5$ at the HL-LHC, shrinking the simplest thermal dark matter scenarios.","Beyond the paper, a monojet or $Z'$ plus initial-state-radiation search could measure $BR_{inv}$ directly and break the coupling-versus-invisible degeneracy the paper identifies."],"forward_implications":["In the minimal model, the ATLAS 139 fb$^{-1}$ dilepton data exclude $M_{Z'}$ below 4 TeV for $g_{BL}=0.1$ and below 6 TeV for $g_{BL}=0.5$.","Turning on $BR_{inv}=0.9$ weakens the $g_{BL}=0.5$ limit to 4.8 TeV, so invisible decays remove only a limited slice of the parameter space.","At every benchmark considered, the LHC bound now supersedes the LEP bound $M_{Z'}/g_{BL} > 7$ TeV.","HL-LHC at 14 TeV with 3 ab$^{-1}$ is projected to probe $M_{Z'}$ up to about 5.7--7.6 TeV depending on coupling and invisible branching ratio.","Dilepton rates alone cannot distinguish models: $g_{BL}=0.3$ with $BR_{inv}=0$ yields the same signal as $g_{BL}=0.5$ with $BR_{inv}=0.7$."],"supporting_citations":[{"why":"Supplies the ATLAS observed 95% C.L. limit curve on dilepton resonances that every exclusion is read off.","marker":"[28]"},{"why":"Provides the MadGraph leading-order simulations used to compute $\\sigma(pp\\to Z')\\times BR(Z'\\to \\ell\\ell)$ over the parameter grid.","marker":"[38]"},{"why":"FeynRules implementation of the $B-L$ Lagrangian that feeds the Monte Carlo event generation.","marker":"[37]"},{"why":"The LEP electroweak combination that established the $M_{Z'}/g_{BL} > 7$ TeV bound against which the LHC limits are compared.","marker":"[39]"},{"why":"The collider reach code used to extrapolate current constraints to HL-LHC conditions.","marker":"[43]"},{"why":"Provides the CTL8NNLO parton distribution functions used for the HL-LHC cross-section projections.","marker":"[44]"}],"fun_headline_variants":["LHC tightens B-L Z' mass limits beyond LEP bounds","ATLAS data exclude B-L Z' up to 6 TeV","B-L Z' boson: LHC beats LEP, HL-LHC hits 7.6 TeV","Invisible decays relax B-L Z' bounds to 4.8 TeV","LHC beats LEP for B-L Z' bounds, HL-LHC extends to 7.6 TeV"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The limits assume a $B-L$ $Z'$ would be reconstructed with the same acceptance and efficiency as the sequential Standard Model $Z'$ in the ATLAS analysis, and that leading-order predictions need no K-factor, PDF, or interference corrections.","fun_headline_variants_meta":{"raw":{"variants":["LHC tightens B-L Z' mass limits beyond LEP bounds","ATLAS data exclude B-L Z' up to 6 TeV","B-L Z' boson: LHC beats LEP, HL-LHC hits 7.6 TeV","Invisible decays relax B-L Z' bounds to 4.8 TeV","LHC beats LEP for B-L Z' bounds, HL-LHC extends to 7.6 TeV"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000607,"raw_usage":{"total_tokens":2869,"prompt_tokens":1027,"completion_tokens":1842,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":643,"completion_tokens_details":{"reasoning_tokens":1726}},"tokens_in":643,"tokens_out":1842,"duration_ms":12181,"temperature":1.0,"reasoning_tokens":1726,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-10T22:47:37.327624+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Recompute the exclusion using the ATLAS binned dilepton likelihood with interference between the $B-L$ $Z'$ and Standard Model Drell-Yan included; if the predicted dilepton yield drops by 20--30%, the mass limits quoted here would move downward by hundreds of GeV.","supporting_citations":[{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"The LEP electroweak combination that established the $M_{Z'}/g_{BL} > 7$ TeV bound against which the LHC limits are compared."}],"review_version":1}