Determination of the Relative Sign of the Higgs Boson Couplings to W and Z Bosons Using WH Production via Vector-Boson Fusion with the ATLAS Detector

The associated production of Higgs and 𝑊 bosons via vector-boson fusion is highly sensitive to the relative sign of the Higgs boson couplings to 𝑊 and 𝑍 bosons. In this Letter, two searches for this process are presented, using 140  fb⁻¹ of proton-proton collision data at √𝑠=13  TeV recorded by the ATLAS detector at the LHC. The first search targets scenarios with opposite-sign couplings of the 𝑊 and 𝑍 bosons to the Higgs boson, while the second targets standard model-like scenarios with same-sign couplings. Both analyses consider Higgs boson decays into a pair of 𝑏 quarks and 𝑊 boson decays with an electron or muon. The data exclude the opposite-sign coupling hypothesis with a significance beyond 5⁢𝜎, and the observed (expected) upper limit set on the cross section for vector-boson fusion 𝑊⁢𝐻 production is 9.0 (8.7) times the standard model value at 95% confidence level.