Measurement and interpretation of inclusive $W\gamma$ production in proton-proton collisions at $\sqrt{s}=13$ TeV using the ATLAS detector

TL;DR

This paper presents precise measurements of Wγ production in proton-proton collisions at 13 TeV using the ATLAS detector, testing Standard Model predictions and constraining new physics via effective field theory operators.

Contribution

It provides detailed differential cross-section measurements for Wγ production, compares them with multiple theoretical models, and sets new limits on anomalous gauge couplings using neural network-based observables.

Findings

Data agree with Standard Model predictions within uncertainties.

Constraints on Wilson coefficients of dimension-six operators are established.

Sensitivity to certain operators is significantly improved over previous measurements.

Abstract

Differential cross-section measurements are presented for the production of a $W$ boson in association with a photon. The analysis is performed using proton--proton collision data collected by the ATLAS experiment at $\sqrt{s}= 13$ TeV, corresponding to an integrated luminosity of 140~fb$^{-1}$. The differential cross sections are measured in the $W\gamma \rightarrow \ell \nu \gamma$ decay channel ($\ell=e,\mu$) as a function of 16 observables. Collectively, these observables probe the kinematic properties of the $W\gamma$ system, the radiation amplitude zero effect predicted for the $W\gamma$ final state, the polarisation of the $W$ boson, the charge conjugation and parity structure of the $WW\gamma$ triple gauge coupling, and the parton distribution functions of the proton. The data are corrected for the effects of detector inefficiency and resolution and are sufficiently precise that they can be used to distinguish between different state-of-the-art theoretical predictions provided by SHERPA, MADGRAPH5_aMC@NLO, and GENEVA. The differential cross sections are used to search for anomalous weak-boson self-interactions induced by dimension-six operators within an effective field theory. For CP-odd operators, dedicated detector-corrected observables based on the outputs of neural networks are found to be particularly sensitive to the interference between the Standard Model and dimension-six scattering amplitudes. Constraints are placed on the Wilson coefficients of the $\mathcal {o}_{W}$, $\mathcal{o}_{HWB}$, $\mathcal{o}_{\tilde{W}}$ and $\mathcal{o}_{H{\tilde{W}B}}$ operators in the effective field theory. The sensitivity to the $\mathcal{o}_{H{\tilde{W}B}}$ operator is improved by a factor of 2.5 compared to previous measurements in other final states.