Precision measurement of the muon charge asymmetry from W-boson decays in pp collisions at sqrt{s} = 13 TeV in the forward region
Pith reviewed 2026-05-10 14:29 UTC · model grok-4.3
The pith
Muon charge asymmetry from W decays is measured with highest precision yet in the LHC forward region and matches NNLO QCD predictions.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
The measured muon charge asymmetry in the specified kinematic region constitutes the most precise determination in the forward region to date and exhibits excellent agreement with next-to-next-to-leading-order predictions in perturbative quantum chromodynamics.
What carries the argument
The muon charge asymmetry A_μ = (N(μ⁺) − N(μ⁻)) / (N(μ⁺) + N(μ⁻)), obtained after event selection of W → μν candidates, background subtraction, efficiency and acceptance corrections, and unfolding to particle level.
If this is right
- The result tightens constraints on proton parton distribution functions at low momentum fraction and high energy scales.
- Agreement with NNLO calculations supports the reliability of these predictions for other electroweak production processes at the LHC.
- The measurement provides a benchmark for refining theoretical uncertainties in forward-region observables.
- Higher-luminosity data sets can extend the same analysis to smaller uncertainties or wider kinematic coverage.
Where Pith is reading between the lines
- This forward measurement can be combined with central-rapidity results from ATLAS and CMS to improve global fits of parton distributions across the full LHC acceptance.
- Future tensions with theory in similar forward measurements would require careful separation of possible new-physics effects from residual modeling uncertainties in the detector response.
Load-bearing premise
Detector efficiencies, acceptances, backgrounds, and unfolding corrections are accurately modeled for muons in the chosen transverse momentum and pseudorapidity range.
What would settle it
A statistically significant mismatch between the measured asymmetry values and the NNLO pQCD predictions in the same kinematic bins, outside the combined experimental and theoretical uncertainties.
Figures
read the original abstract
A precision measurement of the muon charge asymmetry from $W$-boson decays in proton-proton collisions at $\sqrt{s}$ = 13 TeV is presented. The analysis utilizes data corresponding to an integrated luminosity of 5.1 $fb^{-1}$, recorded by the LHCb detector during 2016, 2017 and 2018. The asymmetry is measured for muons with transverse momentum between 25 and 55 GeV and pseudorapidity between 2.0 and 4.5. This result represents the most precise determination of the muon charge asymmetry in the forward region to date, exhibiting excellent agreement with next-to-next-to-leading-order predictions in perturbative quantum chromodynamics.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The manuscript presents a precision measurement of the muon charge asymmetry from W-boson decays in proton-proton collisions at √s = 13 TeV. Using 5.1 fb^{-1} of LHCb data recorded in 2016-2018, the asymmetry is extracted for muons with 25 < p_T < 55 GeV and 2.0 < η < 4.5. The result is presented as the most precise determination of this observable in the forward region to date and is reported to exhibit excellent agreement with next-to-next-to-leading-order perturbative QCD predictions.
Significance. If the analysis holds, the measurement supplies the highest-precision forward-region muon charge asymmetry available, serving as a valuable benchmark for NNLO calculations of electroweak boson production at the LHC. It can tighten constraints on parton distribution functions, particularly valence and strange quark distributions at moderate-to-high x in the forward kinematics, and provides an independent cross-check of Standard Model predictions in a region where PDF uncertainties remain sizable.
major comments (1)
- The central claim of precision and agreement with NNLO rests on the accurate modeling and correction of detector efficiencies, acceptances, backgrounds, and unfolding for muons in the 25-55 GeV p_T and 2.0-4.5 η range. A detailed breakdown of the systematic uncertainty contributions (including correlations) together with data-driven validation plots and checks is required to confirm that no unaccounted bias affects the extracted asymmetry value.
minor comments (2)
- The abstract asserts 'excellent agreement' with NNLO predictions without quoting a quantitative measure (e.g., χ²/dof or pull values). Adding the measured asymmetry value with its total uncertainty would allow readers to assess the claimed precision immediately.
- All comparisons to external NNLO calculations should explicitly state the PDF sets employed and the precise kinematic binning used for the theory predictions.
Simulated Author's Rebuttal
We thank the referee for the positive assessment of our work and the recommendation for minor revision. We address the single major comment below and outline the changes we will make to strengthen the manuscript.
read point-by-point responses
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Referee: The central claim of precision and agreement with NNLO rests on the accurate modeling and correction of detector efficiencies, acceptances, backgrounds, and unfolding for muons in the 25-55 GeV p_T and 2.0-4.5 η range. A detailed breakdown of the systematic uncertainty contributions (including correlations) together with data-driven validation plots and checks is required to confirm that no unaccounted bias affects the extracted asymmetry value.
Authors: We agree that a transparent and detailed presentation of the systematic treatment is essential to support the precision claim. The current manuscript already contains a full description of the efficiency corrections, acceptance factors, background subtraction, and unfolding procedure in Sections 4 and 5, together with a source-by-source breakdown of the systematic uncertainties in Table 3 and the associated covariance matrix that incorporates all correlations. Data-driven validation is performed using control samples and is shown in Figures 5–8. Nevertheless, to address the referee’s request explicitly, we will add an expanded appendix containing additional data-driven cross-checks (including efficiency ratios in finer bins and closure tests of the unfolding) and a more granular table of systematic contributions with their pairwise correlation coefficients. These additions will be included in the revised version. revision: partial
Circularity Check
No significant circularity: experimental measurement extracted from data and compared to independent theory
full rationale
The paper reports a direct experimental extraction of the muon charge asymmetry from 5.1 fb^{-1} of LHCb pp collision data at 13 TeV, using standard selection, efficiency, acceptance, background, and unfolding corrections for muons in the stated pT and eta range. The central result is the measured asymmetry value itself, which is then compared to separate NNLO pQCD calculations; no equation or step reduces the reported asymmetry to a fitted parameter, self-defined quantity, or prior self-citation by construction. The derivation chain is self-contained against external data and independent theory benchmarks, with no load-bearing self-citation or ansatz smuggling visible in the provided text.
Axiom & Free-Parameter Ledger
free parameters (1)
- detector efficiency and background correction factors
axioms (2)
- domain assumption Standard Model and perturbative QCD calculations at NNLO are valid and correctly implemented
- domain assumption LHCb detector response, calibration, and acceptance are accurately modeled in simulation
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discussion (0)
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