Preliminary lifetime measurement of the $B^0_s \rightarrow D_s \mu X$ decay channel

From February 2002 to August 2004, the D\O\ detector has collected about 400~pb$^{-1}$ of high quality $p\bar{p}$ interactions. Using this data, we have reconstructed over 5000 $B^0_s \rightarrow D_s \mu X$ ($D_s \rightarrow \phi \pi$) decays, one of the largest samples of $B^0_s$ candidates in the world. Using this sample, we present a measurement of the $B^0_s$ lifetime that is competitive with the world average lifetime. Published lifetime results of exclusive decays $B^0_s \rightarrow J/\psi \phi$ and $\Lambda^0_b \rightarrow J/\psi \Lambda_0$ are also covered.