Bs Mixing at DØ

The first direct two-sided bound by a single experiment on the oscillation frequency is reported using a sample of semileptonic decays collected between 2002 – 2006 by the Run IIa DØ detector at Fermilab, corresponding to approximately 1 fb-1 of integrated luminosity. The most probable value of the oscillation frequency Δms is found from a likelihood scan to be 19 ps-1 and within the range at the 90% C.L. At the preferred value of 19 ps-1 there is a 2.5σ deviation from a zero amplitude hypothesis.