  The angular distribution of the two-body decay of a boson of unknown
properties is strongly constrained by angular momentum conservation and
rotation invariance, as well as by the nature of the detected decay particles
and of the colliding ones. Knowing the border between the "physical" and
"unphysical" parameter domains defined by these "minimal constraints"
(excluding specific hypotheses on what is still subject of measurement) is a
useful ingredient in the experimental determinations of angular distributions
and can provide model-independent criteria for spin characterizations. In
particular, analysing the angular decay distribution with the general
parametrization for the J = 2 case can provide a model-independent
discrimination between the J = 0 and J = 2 hypotheses for a particle produced
by two real gluons and decaying into two real photons.
