ATLAS has measured how often a W boson is produced together with two jets in proton–proton collisions at an energy of 13 TeV. The analysis uses the full Run‑2 dataset recorded from 2015–2018, corresponding to 140 inverse femtobarns of data. The study focuses on a selection of events where the W boson is most likely produced by vector‑boson fusion, a particular electroweak way of making W bosons that leaves two high‑energy “tag” jets far apart in rapidity.

The researchers selected events with at least two jets, a charged lepton (an electron or a muon) and missing momentum consistent with a neutrino, which together match a W boson decaying to a lepton and a neutrino. Events were collected with single‑electron and single‑muon triggers with transverse momentum thresholds around 24–26 GeV. Simulated events from Monte Carlo generators were used to model the signal and most backgrounds. The largest background comes from mixed strong‑and‑electroweak production of W+jets (often called QCD Wjj), and its rate and shape were constrained using control regions in the data. Backgrounds from misidentified or non‑prompt leptons were estimated with data‑driven methods.

The paper reports a fiducial cross‑section (a rate in a well‑defined phase space) and differential cross‑sections unfolded to particle level. “Unfolded” means the measured distributions are corrected for detector effects so they can be compared to theoretical predictions. Six observables are reported: the transverse momentum of the leading jet and of the charged lepton, and four properties of the two tag jets — their azimuthal angle difference (Δφ_jj), their invariant mass (m_jj), their combined transverse momentum (pT_jj), and the absolute difference in rapidity (|Δy_jj|). The dijet mass m_jj gives the best separation between the electroweak signal and the QCD background, while |Δy_jj| is sensitive to interference between the two production modes. The Δφ_jj variable is highlighted as particularly sensitive to physics beyond the Standard Model.