On Complete Sets of Polarization Observables
  A new criterion is developed which provides a check as to whether a chosen set of polarization observables is complete with respect to the determination of all independent $T$-matrix elements of a reaction of the type $a+b\to c+d+...$. As an illustrative example, this criterion is applied to the longitudinal observables of deuteron electrodisintegration. 
Hartmuth Arenhoevel, Winfried Leidemann, and Edward L. Tomusiak