Angular characterization of the ZZ→4ℓ background continuum to improve sensitivity of new physics searches

The process qq¯→ZZ→4ℓ, dominant background for new physics signals in the four-lepton channel, is characterized by a fully transverse polarization of the two Z bosons with respect to the q and q¯ directions. We show that the Z decay angular distributions can be described by a simple, analytical function of the event kinematics, not depending on parton distributions. Using the search for a heavy Higgs boson as an example, we show that the angular discrimination improves the sensitivity to rare signals and is especially beneficial when the background contribution is large.