First direct two-sided bound on the B0(s) oscillation frequency

The authors report the first direct two-sided bound on the B{sub s}{sup 0} oscillation frequency using a large sample of B{sub s}{sup 0} semileptonic decays corresponding to approximately 1 fb{sup -1} of integrated luminosity collected by the D0 experiment in 2002-2006 during Run II of the Fermilab Tevatron Collider. The flavor (i.e., B{sub s}{sup 0} or B{sub s}{sup 0}) of the B{sub s}{sup 0} meson at the time of production was found using an opposite-side tagging technique, and the flavor at the time of decay was determined from the charge of the muon in the partially reconstructed decay B{sub s}{sup 0} {yields} {mu}{sup +} D{sub s}{sup -}X, D{sub s}{sup -} {yields} {phi}{pi}{sup -}, {phi} {yields} K{sup +}K{sup -}. A likelihood scan over the oscillation frequency, {Delta}m{sub s}, gives a most probable value of 19 ps{sup -1} and a range of 17 < {Delta}m{sub s} < 21 ps{sup -1} at the 90% C.L. At {Delta}m{sub s} = 19 ps{sup -1}, the amplitude method yields a result that deviates from the hypothesis of an oscillation amplitude of zero by 2.5 standard deviations, corresponding to a two-sided C.L. of 1%.