  We propose a new observable designed to probe CP-violating coupling of the
Higgs boson to W bosons using associated Higgs production. We define an
asymmetry that measures the number of leptons from W decays relative to the
plane defined by the beam line and the Higgs boson momentum. The orientation of
that plane is determined by the direction of fermions in the initial state, so
that in a proton-proton collider it requires rapidity cuts that preferentially
select quarks over antiquarks.
