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| id: P06 |
| title: "Reproducing $U_1$ vector-leptoquark $\\sqrt{|g_c^* g_b|}$ vs $M_{U_1}$ exclusion from ATLAS+CMS $pp \\to \\tau\\nu$" |
| arxiv_id: "1811.07920" |
| venue: "ARC-Bench Physics 2026" |
| paper_asset: null |
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| synthesis: | |
| Reproducing the LHC sensitivity to a $U_1$ vector leptoquark from the |
| $pp \to \tau\nu$ channel via $bc \to U_1 \to \tau\nu$ exchange, |
| combining ATLAS + CMS searches in a binned profile-likelihood, as a |
| benchmark of the agent's ability to (i) generate LQ events with |
| bottom-quark and charm-quark initial-state partons, (ii) run two |
| parallel detector-card simulations (Delphes ATLAS card vs CMS card), |
| (iii) recast experimental data into a profile-likelihood fit. The |
| Lagrangian couples $U_1$ to $(\bar c \gamma^\mu P_L \nu_\tau)$ and |
| $(\bar b \gamma^\mu P_L \tau)$ with couplings $g_c, g_b$, and the |
| diagnostic figure is the 2$\sigma$ exclusion contour in the |
| $(\sqrt{|g_c^* g_b|}, M_{U_1})$ plane along with the LH and RH |
| $R_{D^{(*)}}$ flavor-anomaly bands. |
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| A credible study (a) implements the $U_1$ Lagrangian (FeynRules .fr + |
| UFO), (b) runs MadGraph + Pythia8 + Delphes for $M_{U_1} \in \{750, |
| 1000, 1250, 1500, 2000, 2500, 3000, 4000, 5000\}$ GeV with both ATLAS |
| and CMS cards (LHCO output), (c) applies the published ATLAS and CMS |
| $\tau$-channel selections (lepton veto, hadronic-$\tau$ requirement, |
| $E_T^\mathrm{miss}$ cut, $m_T$ cut), (d) builds a binned signal |
| template that scales as $g^4$ and runs the per-bin profile likelihood |
| with nuisance parameters $\theta_i$, (e) combines ATLAS + CMS, finds |
| the 2$\sigma$ exclusion via $-2\Delta\ln\mathcal{L} = 4$, and (f) |
| overlays the analytic LH band $g_\mathrm{LH}(M) = (M/v)\sqrt{2 V_{cb}\, |
| \epsilon_L}$ with $\epsilon_L = 0.11 \pm 0.02$ and the analogous RH band. |
| Research question: *does the agent reproduce the $(\sqrt{|g_c^* g_b|}, |
| M_{U_1})$ exclusion contour and the $R_{D^{(*)}}$ overlay bands of |
| Figure 3 of arXiv:1811.07920?* |
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| hypotheses: |
| - id: H1 |
| statement: "The combined ATLAS+CMS 2$\\sigma$ exclusion at $M_{U_1} = 1$ TeV gives $\\sqrt{|g_c^* g_b|} \\in [0.3, 1.5]$, matching the published value within 30%." |
| measurable: true |
| - id: H2 |
| statement: "The reconstructed exclusion contour intersects the LH $R_{D^{(*)}}$ band ($\\epsilon_L = 0.11$) at an excluded mass $M_{U_1}^* \\in [1.0, 2.5]$ TeV." |
| measurable: true |
| - id: H3 |
| statement: "Selection efficiency on signal events is $\\geq 5\\%$ at $M_{U_1}=1$ TeV in both ATLAS and CMS analyses (gauge of pipeline working end-to-end through Delphes)." |
| measurable: true |
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| experiment_design: |
| research_question: "Does the agent reproduce the 2$\\sigma$ exclusion contour for the $U_1$ vector leptoquark in the $(\\sqrt{|g_c^* g_b|}, M_{U_1})$ plane from combined ATLAS+CMS $pp \\to \\tau\\nu$ recast (Figure 3 of arXiv:1811.07920)?" |
| conditions: |
| - name: "atlas_recast" |
| description: "Mass scan $M_{U_1} \\in \\{750, 1000, 1250, 1500, 2000, 2500, 3000, 4000, 5000\\}$ GeV at $\\sqrt{s}=13$ TeV, 10k events each, Pythia8 shower, Delphes ATLAS card, LHCO output. Selection: lepton veto, hadronic-$\\tau$ $p_T > 80$ GeV, $|\\eta_\\tau| < 2.3$, $E_T^\\mathrm{miss} > 150$ GeV, $m_T > 250$ GeV." |
| - name: "cms_recast" |
| description: "Same mass scan with Delphes CMS card; selection: lepton veto, $\\tau$ $p_T>80$ GeV, $|\\eta|<2.1$, $E_T^\\mathrm{miss}>200$ GeV, $0.7 < p_T^\\tau / E_T^\\mathrm{miss} < 1.3$, $\\Delta\\phi(\\tau, E_T^\\mathrm{miss}) > 2.4$, $m_T > 320$ GeV." |
| baselines: |
| - "Published ATLAS background table (22 bins, 250-3200 GeV log-spaced) and CMS background table (3 bins) act as the SM-only null hypothesis" |
| metrics: |
| - name: "exclusion_coupling_at_1tev" |
| direction: "match_reference" |
| description: "$\\sqrt{|g_c^* g_b|}$ at the 2$\\sigma$ exclusion boundary at $M_{U_1}=1$ TeV from combined fit." |
| - name: "selection_efficiency" |
| direction: "match_reference" |
| description: "Fraction of generated signal events passing the ATLAS or CMS selection at $M_{U_1}=1$ TeV." |
| - name: "rdstar_band_intersection_tev" |
| direction: "match_reference" |
| description: "Mass at which the LH $R_{D^{(*)}}$ band crosses the exclusion contour." |
| datasets: |
| - process_id: "pp_to_taunu_via_U1" |
| sqrt_s_TeV: 13 |
| description: "$pp \\to \\tau\\nu$ via $bc \\to U_1$ exchange. Two detector simulations (Delphes ATLAS, Delphes CMS)." |
| compute_requirements: |
| gpu_required: false |
| estimated_wall_clock_sec: 3600 |
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| rubric_path: "experiments/arc_bench/config/physics/rubrics/P06.json" |
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| requirements: |
| - id: req_results_json |
| type: artifact |
| description: >- |
| A canonical results.json file exists at the workspace root with at least |
| the keys: primary_metric (number), metric_key (string), metrics (object |
| with numeric keys), hypotheses (object with h1/h2/h3 entries each |
| carrying a `supported` boolean), summary (non-empty string). |
| must_pass: true |
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|
| - id: req_metrics_numeric |
| type: numeric |
| description: >- |
| results.json metrics MUST contain at least 3 numeric (non-null, finite) |
| values directly relevant to the headline physics observable named in |
| the experiment_design.metrics list above — these are the numbers the |
| paper will report in its Results section. |
| must_pass: true |
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| - id: req_hypotheses_supported_flags |
| type: discussion |
| description: >- |
| results.json hypotheses.h1/h2/h3 each MUST have an explicit `supported` |
| boolean AND a `details` string ≥ 40 characters quoting the numerical |
| evidence (specific values + their source artifact) used to reach the |
| verdict. |
| must_pass: true |
|
|
| - id: req_publication_figure |
| type: artifact |
| description: >- |
| At least one publication-quality figure file (PDF or PNG, ≥150 DPI for |
| raster) exists under figures/ or output/figures/ with axes labeled in |
| physical units (GeV / pb / fb / dimensionless) and a legend if multiple |
| series are plotted. The figure must directly support a hypothesis |
| verdict. |
| must_pass: true |
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| - id: req_model_implementation |
| type: artifact |
| description: >- |
| The BSM Lagrangian is implemented either as a FeynRules .fr file |
| (models/*.fr) with a matching UFO directory (models/*_UFO/ containing |
| at least particles.py, parameters.py, couplings.py, vertices.py), OR |
| as analytic Python code that explicitly computes the cross sections |
| from the Lagrangian terms. A pure SM baseline with no BSM piece is |
| NOT sufficient. |
| must_pass: true |
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| - id: req_lq_coupling_band |
| type: numeric |
| description: >- |
| results.json metrics MUST report the 2σ combined ATLAS+CMS √(g_c* g_b) exclusion band at M_U1=1 TeV; the band lower edge must be in [0.21, 0.39] and the upper edge in [1.05, 1.95] (published [0.3, 1.5] ±30%). |
| must_pass: true |
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|
| - id: req_mechanistic_writeup |
| type: discussion |
| description: >- |
| The summary or structured_results section provides a one-paragraph |
| mechanistic interpretation of WHY the headline observable comes out the |
| way it does (which interference / propagator structure / cut effect |
| drives the result). Nice-to-have, not blocking proceed. |
| must_pass: false |
|
|
| - id: req_mc_reproducibility |
| type: discussion |
| description: >- |
| results.json or a sibling reproducibility section names: (a) the |
| MadGraph5_aMC@NLO version, (b) the PDF set used (if applicable), (c) |
| at least one explicit random seed. Required for full reproducibility |
| but not for scientific correctness. |
| must_pass: false |
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