Proton-antiproton annihilation into massive leptons
  We extend previous calculations of polarization observables for the annihilation reaction $\bar p +p\to \ell^{-}+\ell^{+}$ to the case of heavy leptons, such as the $\tau$-lepton. We consider the case when the beam and/or the target are polarized, as well as the polarization of the outgoing leptons. We give the dependence of the unpolarized cross section, angular asymmetry, and various polarization observables on the relevant kinematical variables in the center of mass and in the laboratory system, with particular attention to the effect of the mass induced terms. 
A. Dbeyssi, E. Tomasi-Gustafsson, G. I. Gakh, M. Konchatnyi
hep-ph nucl-th