Reproducing the normalized $E_T^\mathrm{miss}$ shape in $pp \to a W^\pm \gamma$ from a photophobic ALP EFT
Domain: physics (high-energy-physics, bsm-phenomenology, axion-like-particles, effective-field-theory)
Topic: Reproducing photophobic ALP EFT $E_T^\mathrm{miss}$ shape in $pp \to a W^\pm \gamma$ from arXiv:1701.05379
Venue: ARC-Bench Physics 2026
Source paper: arXiv 1701.05379
Headline metric: primary_metric (maximize)

Research briefing:
Reproducing the normalized $E_T^\mathrm{miss}$ distribution for the
process $pp \to a W^\pm (\to \ell^\pm \nu)\, \gamma$ at $\sqrt{s}=13$
TeV in the bosonic ALP EFT, as a benchmark of the agent's ability to
handle a higher-dimensional EFT operator and parton-level missing-energy
reconstruction. The Lagrangian is
$\delta\mathcal{L}_a = c_{\tilde W} \mathcal{A}_{\tilde W} +
c_{\tilde B} \mathcal{A}_{\tilde B}$ with the photophobic constraint
$c_{\tilde B} = -\tan^2\theta_W \cdot c_{\tilde W}$ (so the
$a\gamma\gamma$ coupling vanishes), giving a single free Wilson
coefficient $c_{\tilde W}$. The diagnostic observable is the
normalized parton-level $E_T^\mathrm{miss} = |\vec p_T^{\,a} +
\vec p_T^{\,\nu}|$ shape in 50 bins over [0, 1000] GeV, with
generation cuts $p_T^{\gamma,\ell} > 20$ GeV, $|\eta^{\gamma,\ell}| < 2.5$.

A credible study (a) implements the photophobic ALP EFT (FeynRules
bosonic operators with $c_{\tilde B} = -\tan^2\theta_W \cdot c_{\tilde W}$),
(b) generates 500k LHE events at $f_a = 1000$ GeV, $m_a = 0.001$ GeV,
$c_{\tilde W} = 1$ with the nn23lo1 PDF, (c) sums $\vec p_T^{\,a}$ +
$\vec p_T^{\,\nu}$ from invisible final-state particles to reconstruct
$E_T^\mathrm{miss}$, and (d) plots the normalized histogram on log-y
$[10^{-4}, 1]$ over [0, 1000] GeV. Research question: *does the agent
reproduce the falling-then-flattening MET shape characteristic of a
derivative ALP coupling versus the steeply falling SM-like baseline,
matching Figure 8 of arXiv:1701.05379?*

Hypotheses:
statement: The peak of the normalized $E_T^\mathrm{miss}$ distribution lies in the bin range $[100, 250]$ GeV, consistent with the published shape., statement: The integrated normalized fraction of events with $E_T^\mathrm{miss} > 500$ GeV is in $[0.05, 0.30]$ at $c_{\tilde W}=1$, $f_a=1$ TeV (long high-MET tail from the derivative ALP coupling)., statement: Acceptance after the published photon and lepton cuts ($p_T > 20$ GeV, $|\eta| < 2.5$) is $\geq 50\%$ of generated events.

Experiment design:
research_question: Does the agent reproduce the parton-level $E_T^\mathrm{miss}$ shape for $pp \to a W^\pm \gamma$, $W \to \ell\nu$ at $\sqrt{s}=13$ TeV under the photophobic ALP EFT (Figure 8 of arXiv:1701.05379)?
conditions: name: alp_cw1_fa1tev
description: Bosonic ALP EFT at $c_{\tilde W}=1$, $c_{\tilde B}=-\tan^2\theta_W$, $f_a=1000$ GeV, $m_a=0.001$ GeV, 500k events at $\sqrt{s}=13$ TeV with nn23lo1 PDF., name: alp_cw_variant
description: Sanity-check run at $c_{\tilde W}=2$, $f_a=1000$ GeV; cross section should scale as $c_{\tilde W}^2$ but normalized shape should be invariant.
baselines: Shape-only normalization is its own baseline: deviation between $c_{\tilde W}=1$ and $c_{\tilde W}=2$ shapes should be statistical only
metrics: name: etmiss_peak_position_gev
direction: match_reference
description: $E_T^\mathrm{miss}$ bin center of the peak of the normalized histogram., name: high_metmiss_tail_fraction
direction: match_reference
description: Fraction of normalized events with $E_T^\mathrm{miss} > 500$ GeV., name: cut_acceptance
direction: match_reference
description: Acceptance fraction after photon + lepton fiducial cuts.
datasets: process_id: pp_to_aWgamma_Wlnu
sqrt_s_TeV: 13
description: Parton-level $pp \to a W^\pm \gamma$ with $W \to \ell\nu$ in the photophobic ALP EFT.
compute_requirements: gpu_required: no
estimated_wall_clock_sec: 3600

Requirements:
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)., 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., 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., 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., 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., type: numeric
description: results.json metrics MUST report the peak bin of the normalized E_T^miss distribution; the bin center must lie in [100, 250] GeV and the distribution must integrate to 1.0 (normalized)., 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., 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.

Scoring rubric:
requirements: A credible HEP collider study reproducing the published reference figure for Photophobic ALP EFT $E_T^\mathrm{miss}$ in $pp \to a W^\pm \gamma$. The agent must (a) implement the BSM Lagrangian, (b) generate Monte Carlo events for the specified process with appropriate PDFs and generation cuts, (c) run the necessary detector / shower simulation if required, (d) reconstruct the diagnostic kinematic distribution, and (e) compare against the published reference figure with quantitative residuals tied to H1, H2, H3.
judging_note: Physics topics are scored on whether the agent (i) assembles a working HEP MC pipeline AND (ii) reproduces the published numbers within stated tolerance. Partial credit is allowed; the agent may use analytic shortcuts in place of MadGraph for cases where it is overkill, as long as the answer matches the published reference within the per-leaf tolerance. Quantitative result leaves are scored on a graded scale: 100% if relative error < 3%, 67% if < 10%, 33% if < 30%, 0% otherwise.
sub_tasks: requirements: Code-development bucket: BSM model + process card + PDF/cuts + full pipeline are wired correctly.
sub_tasks: requirements: BSM Lagrangian implemented (FeynRules .fr file + UFO output, or equivalent analytic Python module): Bosonic ALP EFT operators $\mathcal{A}_{\tilde W}, \mathcal{A}_{\tilde B}$ with photophobic relation $c_{\tilde B} = -\tan^2\theta_W \cdot c_{\tilde W}$; $f_a = 1$ TeV, $m_a = 1$ MeV, $c_{\tilde W} = 1$.
task_category: Code Development
finegrained_task_category: Method Implementation, requirements: MadGraph generate-process card or analytic process module matches the paper's process string: Parton-level $pp \to a W^\pm (\to \ell^\pm\nu) \gamma$ at $\sqrt{s}=13$ TeV.
task_category: Code Development
finegrained_task_category: Method Implementation, requirements: PDF set and generation-level cuts match the paper exactly: nn23lo1 PDF; photon $p_T > 20$ GeV, $|\eta_\gamma| < 2.5$; lepton $p_T > 20$ GeV, $|\eta_\ell| < 2.5$; 500k events, parton level (no shower/detector).
task_category: Code Development
finegrained_task_category: Experimental Setup, requirements: Full HEP chain wired together (model -> events -> [shower -> detector] -> reconstruction -> analysis -> figure). For analytic shortcuts the chain may be simpler but must still terminate in the diagnostic figure.
task_category: Code Development
finegrained_task_category: Method Implementation, requirements: Execution-validity bucket: MC sample passes nevents threshold, physics-validity gates clear, MC stats are sufficient.
sub_tasks: requirements: MC sample(s) generated successfully with at least the requested number of events per cell (or a documented partial count if compute-limited), with no fatal MadGraph or downstream errors.
task_category: Code Execution
finegrained_task_category: Evaluation, Metrics & Benchmarking, requirements: Physics-validity gate: no negative cross sections; gauge invariance / unitarity sanity checks pass; mass spectrum and decay widths printed by MadGraph match the input parameter card; no obviously unphysical kinematics in the generated events.
task_category: Code Execution
finegrained_task_category: Evaluation, Metrics & Benchmarking, requirements: MC statistics are sufficient: relative MC error in the signal region is < 10% OR at least 3 random seeds are run with std reported across them.
task_category: Code Execution
finegrained_task_category: Evaluation, Metrics & Benchmarking, requirements: Results bucket: quantitative comparison of three hypothesis-driven observables to the published figure, plus a reproduced figure artifact and a per-hypothesis writeup.
sub_tasks: requirements: Quantitative test of H1 — Peak of normalized $E_T^\mathrm{miss}$ in $[100, 250]$ GeV bin range.
task_category: Result Analysis
finegrained_task_category: Logging, Analysis & Presentation, requirements: Quantitative test of H2 — Integrated normalized fraction with $E_T^\mathrm{miss} > 500$ GeV in $[0.05, 0.30]$ (long high-MET tail from derivative coupling). Use the same graded relative-error scale as H1.
task_category: Result Analysis
finegrained_task_category: Logging, Analysis & Presentation, requirements: Quantitative test of H3 — Acceptance after photon + lepton cuts $\geq 50\%$. Use the same graded relative-error scale as H1.
task_category: Result Analysis
finegrained_task_category: Logging, Analysis & Presentation, requirements: A reproduced figure exists in artifacts (PDF or PNG) with axes, units, ranges, and legend matching the published reference: Normalized $E_T^\mathrm{miss}$ histogram, 50 bins over [0,1000] GeV, log-y $[10^{-4}, 1]$, 4:3 aspect.
task_category: Result Analysis
finegrained_task_category: Logging, Analysis & Presentation, requirements: Writeup discusses the outcome of each hypothesis (supported / refuted / inconclusive) tied to numeric residuals, identifies the dominant systematic uncertainty (PDF set, scale variation, k-factor, Delphes card, statistical MC error), and states explicitly any analytic shortcuts taken in place of full MC.
task_category: Result Analysis
finegrained_task_category: Logging, Analysis & Presentation, requirements: Reproducibility bucket (new for physics topics; absent in T-rubrics): the artifacts contain everything needed to rerun the analysis from scratch.
sub_tasks: requirements: UFO model directory (or analytic model Python module) is checked into the artifacts and is loadable by MadGraph (or directly importable for analytic models).
task_category: Code Development
finegrained_task_category: Reproducibility, requirements: MadGraph run_card / param_card, Pythia8 settings, Delphes card, and MadAnalysis5 (or equivalent analysis) cards are saved alongside the run with explicit parameter values per cell.
task_category: Code Development
finegrained_task_category: Reproducibility, requirements: RNG seeds are documented; rerunning the run from saved seeds should give matching central values within the reported MC error. For analytic shortcuts, the seed requirement is replaced by an explicit list of input numerical parameters.
task_category: Code Development
finegrained_task_category: Reproducibility