Determining Spin through Quantum Azimuthal-Angle Correlations
  Determining the spin of new particles is critical in identifying the true theory among various extensions of the Standard Model at the next generation of colliders. Quantum interference between different helicity amplitudes was shown to be effective when the final state is fully reconstructible. However, many interesting new physics processes allow only for partial reconstruction. In this paper, we show how the interference effect can be unambiguously extracted even in processes that have two-fold ambiguity, by considering the correlation between two decay planes in e+ e- collisions. 
Matthew R. Buckley, Seong Youl Choi, Kentarou Mawatari, and Hitoshi   Murayama