{"id":"bcfa2f58-6cd5-41ce-84d3-70d67372a7a1","arxiv_id":"2412.06298","paper_version":1,"verdict":"UNVERDICTED","confidence":"MODERATE","novelty_score":2.0,"correctness_risk":"low","formal_verification":"none","parameter_count":0,"one_line_summary":"Analyzing 138 fb-1 of 13 TeV CMS data, the two searches observe no excess and set new upper limits on heavy neutral lepton mixing, including first tau-coupling coverage above the W mass.","lead":"This CMS conference report summarizes two searches for heavy neutral leptons, hypothetical particles that might explain neutrino masses and other open problems. Using machine learning in trilepton and displaced dilepton final states, it finds no excess and sets new exclusion limits on how strongly such particles mix with known neutrinos.","discovery_kind":"review","skeptic_critique":{"model":"deepseek-v4-flash","headline":"No significant objection identified.","rationale":"The reader set the verdict to UNVERDICTED because the text alone does not permit independent statistical verification. I agree that the manuscript is not a self-contained derivation, but it is a conference proceedings that explicitly delegates to Refs. [5] and [6] for the full analyses. The central claim of the summary—that CMS observes no significant deviation and sets limits—is supported by those references, and I find no internal inconsistency or unsupported assertion in the summary itself. The reader's weakest assumptions (production model and ABCD closure) are indeed the points on which any HNL search ultimately rests, but they are not flaws in this summary; they are standard assumptions validated in the cited papers. The summary does not overclaim: it states limits for specific coupling scenarios, notes that the tau-coupling reach above the W mass is new, and references earlier results for comparison. Since no load-bearing concern lands, the appropriate action is to leave the reader's UNVERDICTED verdict unchanged. A useful sanity check would be to verify a few numbers from the published exclusion tables to confirm the summary's figures, but this is a routine consistency check rather than a response to a substantive objection.","tokens_in":4000,"tokens_out":8822,"duration_ms":93223,"concrete_test":"Cross-check the reported exclusion limits at a few mass points (e.g., m_N = 20, 100, 500 GeV) in Fig. 3 upper panels against the published limit tables in Ref. [5], and verify that the displaced-search ABCD closure test in Ref. [6] is performed in a control region disjoint from the signal region with predicted/observed agreement within uncertainties.","verdict_should_be":"UNCHANGED","load_bearing_attack":"This manuscript is a proceedings summary of two peer-reviewed CMS analyses (Refs. [5] and [6]). The central claim—that no significant deviation is observed and that 95% CL limits are set on |V_lN|^2—is a faithful restatement of results already published elsewhere. The summary is internally consistent: the mass ranges (10 GeV–1.5 TeV prompt, 1–20 GeV displaced) are clearly stated, the ML methods are described at summary level, and the limit figures are attributed to the referenced papers. The weakest assumptions (Drell–Yan W→lN production, and ABCD sideband closure in the displaced search) belong to the underlying analyses, which are not reproduced here; however, the summary makes no independent statistical claims and does not omit a caveat that would change the interpretation. No statement in the manuscript contradicts its references or overclaims what the cited papers establish. I therefore identify no load-bearing concern that would alter the reader's verdict.","agreement_with_reader":"partial"},"referee_report":{"model":"deepseek-v4-flash","summary":"This proceedings contribution by J. Knolle on behalf of the CMS Collaboration summarizes two CMS searches for heavy neutral leptons (HNLs) using 138 fb^-1 of 13 TeV proton-proton collision data. The prompt trilepton search covers HNL masses from 10 GeV to 1.5 TeV and uses boosted decision trees with up to 43 kinematic variables; the displaced dilepton search covers 1-20 GeV and uses particle-flow networks together with an ABCD method. The paper reports that no significant deviations from the standard model background are observed and presents 95% CL exclusion limits on the HNL mixing parameter |V_lN|^2 for Dirac and Majorana HNLs under different coupling scenarios. It further states that the prompt search gives the most stringent limits over a wide mass range and probes exclusive tau-neutrino couplings above the W mass for the first time. The manuscript is a faithful, high-level summary of Refs. [5] and [6] rather than a new standalone analysis.","tokens_in":4114,"tokens_out":7756,"duration_ms":80769,"significance":"If taken at face value, the summarized results exclude a substantial region of HNL parameter space, and the claimed extension of exclusive tau-coupling limits above the W mass is of phenomenological interest. The paper's value lies in providing a concise, readable entry point to two detailed CMS analyses, and it correctly attributes all results to the cited references. I considered the stress-test concern that the reported limits depend on Drell-Yan W->lN production and on the closure of the ABCD sideband extrapolation; in my reading this does not identify a defect in the present manuscript, because the paper makes no independent statistical claim and explicitly relies on Refs. [5] and [6] for the supporting evidence. The absence of systematic tables, closure tests, and full statistical machinery is appropriate for a conference proceedings contribution.","major_comments":[],"minor_comments":[{"comment":"Section 1 refers to the second search as \"published in Ref. [6]\", but the reference list describes Ref. [6] as \"Submitted to JHEP\". Please correct the wording or update the reference status so that the two statements are consistent.","section":"References, Ref. [6]"},{"comment":"The text says the PFN score is \"one of two variables\" in the ABCD method but never names the second variable in the body; it appears only in the figure label as m(l,SV). Please state explicitly that the second variable is the invariant mass m(l,SV) and define it in the text.","section":"Section 3"},{"comment":"The legend entries in Fig. 2 (right) include unexplained abbreviations such as \"VDY\" and \"HNL3/HNL5/HNL6/HNL10\". Please expand these labels or explain them in the caption so that the background and signal samples are identifiable without consulting Ref. [6].","section":"Fig. 2 (right)"},{"comment":"The upper panels of Fig. 3 show many overlapping curves from different CMS searches, and the luminosity label \"35.9 138fb-1\" is ambiguous. Please clarify which data sets correspond to which curves and distinguish the observed and expected curves of the prompt trilepton search more clearly.","section":"Fig. 3"},{"comment":"The body text contains numerous missing spaces between words, for example \"13TeV\", \"ppcollision\", \"trackercanbereconstructed\", and \"HNLdecay\". If this reflects the compiled PDF rather than an extraction artifact, the LaTeX source should be fixed so that the proceedings text is properly typeset.","section":"Throughout (Sections 1-4)"},{"comment":"The phrase \"results exceed previous limits\" is ambiguous: exclusion limits can be described as stronger, more stringent, or surpassing previous limits. Please rephrase to avoid a reading in which the limits are numerically larger rather than more constraining.","section":"Abstract and Section 4"}],"recommendation":"minor_revision","confidential_remarks":"This is a standard conference proceedings contribution whose scientific content is fully inherited from Refs. [5] and [6]. I have no substantive scientific concern about the summary, and I would not require the authors to include the full statistical details of the underlying analyses. The minor revision is driven by the inconsistent publication status of Ref. [6], a few figure/caption clarity issues, and text formatting problems. For a primary research journal this paper would be too thin, but for LHCP proceedings it is appropriate after the minor corrections."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Quick take: this is a clean, honest proceedings summary of two already-published CMS HNL searches. There is no new measurement, no new derivation, no new dataset. The value is archival/reference, not original research. The summary is internally consistent, the figures are attributed properly, and I see no overclaiming or circularity. It does what a conference proceedings should do.\n\nWhat's good: the two analyses are clearly described—prompt trilepton with BDTs, displaced dilepton with PFNs and the ABCD method. The mass ranges and coupling scenarios are right. The plots are taken from the cited papers and labeled as such. The claim about first coverage of tau couplings above the W mass is from Ref. [5]; I don't see a reason to doubt it here. The text mirrors the underlying analyses without obvious contradiction.\n\nSoft spots: the paper has no independent verifiability, which is expected for a proceedings. No systematics, no closure tests, no fit details. If a reader wanted to evaluate the limits, they'd have to go to Refs. [5] and [6]. The abstract says 'In several cases, the results exceed previous limits' without specifying which cases; that's minor editorial vagueness, not a flaw. The production model assumption (Drell-Yan W->lN) belongs to the underlying analyses, and the proceedings does not need to defend it. I agree with the stress-test: no load-bearing concern. The reader's assessment is sound.\n\nMy recommendation: this does not deserve peer review as a research article. It is a proceedings summary; the original analyses were already refereed. I would not send this to referees if it were submitted to a journal. For the proceedings, it is a normal contribution. Would I cite it? No—I would cite the original JHEP papers. Reading group? Nothing new to chew on. But within its genre, it is a perfectly fine piece of work.","headline":"A faithful, internally consistent proceedings summary of two already-published CMS HNL searches; it adds no new physics but should not be judged as a standalone research paper.","tokens_in":4631,"tokens_out":2320,"would_cite":false,"duration_ms":24818,"reading_group":"no","serious_thinker":"yes","would_accept_peer_review":false},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":["14.60.Pq","14.60.St"],"model":"deepseek-v4-flash","headline":"CMS searches for heavy neutral leptons find no signal and set new exclusion limits.","keywords":["heavy neutral leptons","CMS","trilepton search","displaced dilepton search","machine learning","boosted decision trees","particle flow networks","exclusion limits"],"falsifier":"If a future experiment or a reprocessing of CMS data found a resonant excess in the trilepton or displaced-dilepton spectrum at a mass and mixing already excluded by these curves, the exclusion would be wrong. A direct check is a closure test: in a background-dominated control sample, compute the ABCD prediction from the two sidebands and compare it with the observed yield in the corresponding signal-like box; a significant mismatch would invalidate the displaced search's background estimate and its limits.","tokens_in":3796,"feed_emoji":"⚛️","tokens_out":11293,"duration_ms":102106,"temperature":0.7,"pith_summary":"Two CMS searches for heavy neutral leptons (HNLs) in 138 fb⁻¹ of 13 TeV proton-proton collision data are presented, one for promptly decaying HNLs in the 10 GeV to 1.5 TeV mass range and one for long-lived HNLs of 1 to 20 GeV with displaced decays. Both searches use machine-learned discriminators to suppress standard model backgrounds, and both observe no significant deviation from the background expectation. The results are expressed as 95% confidence-level exclusion limits on the coupling strength $|V_{\\ell N}|^2$ as a function of HNL mass, and in several coupling scenarios they improve on previous limits. The notable new territory is the first probe of exclusive tau-neutrino couplings for HNL masses above the W boson mass, which had not been covered before.","feed_headline":"CMS finds no heavy neutrinos, tightens limits from 1 GeV to 1.5 TeV","feed_subtitle":"ML-based trilepton and displaced-dilepton searches exclude many couplings, including the first tau-only limits above the W mass.","key_machinery":"The machinery is the machine-learned discriminator paired with a data-driven background estimate. In the prompt search, boosted decision trees (BDTs) with up to 43 kinematic input variables are trained separately for mass ranges, coupling scenarios, and final-state flavour combinations, and the BDT score distributions enter maximum-likelihood fits. In the displaced search, particle flow networks (PFNs) — deep networks that act on unordered sets of up to 50 reconstructed particles plus event-level variables — produce a score that, together with the lepton–secondary-vertex invariant mass $m(l,\\mathrm{SV})$, defines signal and sideband regions for the ABCD method. These discriminators are what separate a small HNL signal from large standard model backgrounds and turn event counts into exclusion limits.","core_discovery":"The central claim is that, with 138 fb⁻¹ of 13 TeV data, CMS finds no evidence of heavy neutral leptons and therefore excludes HNL couplings that previous searches had left open. The prompt trilepton analysis, based on boosted decision tree scores in maximum-likelihood fits, yields the most stringent limits over a wide mass range. The displaced dilepton analysis, based on particle flow network scores and an ABCD background estimate, provides competitive limits that are particularly important for long-lived HNLs with masses of 10 to 20 GeV. For a Majorana HNL coupling exclusively to tau neutrinos, the prompt search reaches above the W mass for the first time, extending beyond the earlier DELPHI bound.","pith_inferences":["The same PFN-plus-ABCD recipe could be transplanted to other long-lived particle searches, such as hidden-sector scalars or dark photons, by re-training the discriminator on the alternative signal model; the background machinery would not need to change.","A direct extension of the tau-exclusive result is to push the same search to lower masses and mixings with Run 3 data, since the BDT training is already separated by coupling scenario.","The displaced search's validity hinges on the ABCD assumption; a public closure check in control samples enriched in top-quark and diboson production would make the claim testable at the level of the background model.","Cross-interpreting the two searches at their boundary (masses near 10 to 20 GeV) could yield a combined HNL limit that is stronger than either channel alone, an analysis the paper does not perform."],"forward_implications":["If the limits are correct, HNLs with masses from about 1 GeV to 1.5 TeV are ruled out at 95% confidence for the tested mixing strengths in the electron- and muon-coupling scenarios.","The prompt trilepton channel becomes the most stringent constraint over a wide mass interval, superseding the earlier same-sign and displaced-lepton CMS searches shown for comparison.","The first tau-exclusive exclusion above the W boson mass closes a region of parameter space that had been open since the DELPHI experiment.","The displaced dilepton channel provides the strongest constraint for long-lived HNL scenarios at 10 to 20 GeV, where prompt and displaced searches overlap."],"supporting_citations":[{"why":"Supplies the prompt trilepton search, its BDT-based analysis, and the 10 GeV to 1.5 TeV exclusion limits.","marker":"[5]"},{"why":"Supplies the displaced dilepton search, its PFN-based ABCD analysis, and the 1 to 20 GeV limits.","marker":"[6]"},{"why":"Provides the earlier DELPHI tau-coupling bounds that the prompt search extends above the W mass.","marker":"[13]"},{"why":"Earlier CMS same-sign dilepton search used as a comparison baseline in the electron and muon exclusion plots.","marker":"[7]"},{"why":"Earlier CMS search with a prompt lepton plus displaced leptons used as a comparison baseline for the new limits.","marker":"[8]"}],"fun_headline_variants":["CMS excludes heavy neutrinos from 1 GeV to 1.5 TeV","No heavy neutrinos: CMS tightens limits from 1 GeV to 1.5 TeV","First tau-only heavy neutrino limits above W mass from CMS","CMS machine learning search finds no heavy neutrinos","Heavy neutrinos remain elusive: CMS expands exclusion range"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"Both searches assume HNLs are produced through a Drell–Yan W boson decaying to a lepton and the HNL, with the production rate and lifetime set by the same mixing parameter $|V_{\\ell N}|^2$; the displaced search further assumes its ABCD method can extrapolate the background from the sidebands, defined by the particle-flow-network score and the lepton–secondary-vertex mass, into the signal region.","fun_headline_variants_meta":{"raw":{"variants":["CMS excludes heavy neutrinos from 1 GeV to 1.5 TeV","No heavy neutrinos: CMS tightens limits from 1 GeV to 1.5 TeV","First tau-only heavy neutrino limits above W mass from CMS","CMS machine learning search finds no heavy neutrinos","Heavy neutrinos remain elusive: CMS expands exclusion range"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.00065,"raw_usage":{"total_tokens":2937,"prompt_tokens":858,"completion_tokens":2079,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":474,"completion_tokens_details":{"reasoning_tokens":1986}},"tokens_in":474,"tokens_out":2079,"duration_ms":17114,"temperature":1.0,"reasoning_tokens":1986,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-11T19:47:50.510688+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"If a future experiment or a reprocessing of CMS data found a resonant excess in the trilepton or displaced-dilepton spectrum at a mass and mixing already excluded by these curves, the exclusion would be wrong. A direct check is a closure test: in a background-dominated control sample, compute the ABCD prediction from the two sidebands and compare it with the observed yield in the corresponding signal-like box; a significant mismatch would invalidate the displaced search's background estimate and its limits.","supporting_citations":[{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Provides the earlier DELPHI tau-coupling bounds that the prompt search extends above the W mass."}],"review_version":1}