  We propose a fully flexible method to perform an hypothesis test between
signal and background based on the Matrix Element Method in the presence of
multiple invisible particles. The proposed method performs a mapping of the
measured final state onto its minimal hypersurface of degrees of freedom for a
given process and then maximises the matrix element on this hypersurface
separately for signal and background. To show how performant the method is in
separating signal from background, we apply it to the prominent partly
invisible decay of a Higgs boson into a muon-antimuon pair and two
muon-neutrinos via two W bosons.
