Rotation-invariant relations in vector meson decays into fermion pairs

The covariance properties of angular momentum eigenstates imply the existence of a rotation-invariant relation among the parameters of the di-fermion decay distribution of inclusively observed vector mesons. This relation is a generalization of the Lam-Tung identity, a result specic to Drell-Yan production in perturbative QCD, here shown to be equivalent to the dynamical condition that the dilepton is always produced transversely polarized with respect to quantization axes belonging to the production plane.