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 (VBF) 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 decays into a pair of b-quarks and W decays with an electron or muon. The opposite-sign coupling hypothesis is excluded with significance much greater than 5σ, and the observed (expected) upper limit set on the cross-section for VBF WH production is 9.0 (8.7) times the Standard Model value.