Weak Phase γ from B_s(t) to K^+ K^-

We re-examine the time-dependent rates of $\bs(t) \to K^+ K^-$ and $\obs(t) \to K^+ K^-$, including a lifetime difference between neutral $\bs$ mass eigenstates. The two rates, normalized by the rate of $\bs \to \ko \ok$, are used to obtain ambiguity-free information on a strong phase and on the weak phase $\gamma$. We discuss the sensitivity of extracting $\gamma$ to the measured quantities, and find that an error of $\pm 10^\circ$ in $\gamma$ is possible for a sample of several thousand $\bs(t) \to K^+ K^-$ decays. This study is complementary to a recent similar analysis of the U-spin related decays $\bo(t) \to \pi^+\pi^-$ and $\ob(t) \to \pi^+\pi^-$.