Angular distributions and lifetime differences in $B_s \to J/\psi \phi$ decays

The strange $B$ meson $B_s \equiv \bar b s$ and its charge-conjugate $\bar B_s \equiv b \bar s$ are expected to mix with one another in such a way that the mass eigenstates $B_s^H$ (``heavy'') and $B_s^L$ (``light'') may have a perceptible lifetime difference of up to 40\%, with the CP-even eigenstate being shorter-lived. A simple transversity analysis permits one to separate the CP-even and CP-odd components of $B_s \to J/\psi \phi$, and thus to determine the lifetime difference. The utility of a similar analysis for $B^0 \to J/\psi K^{*0}$ is noted.