Joint Angular Distribution of B_s -> J/\psi \phi with Subsequent \phi -> \rho \pi and J/\psi -> \ell^+ \ell^- Decays

The covariant density matrix formalism is used to obtain the joint angular distribution of the decay B_s -> J/\psi \phi(1020) with subsequent \phi -> \rho \pi and J/\psi -> \ell^+ \ell^- decays. The result is shown algebraically to be a special case of our previous work on the decay distribution of B_d -> J/\psi K_1(1270) with K_1 -> K \pi and J/\psi -> \ell^+ \ell^-.