Observation of B s 0 - B̄ s 0 oscillations

We report the observation of B{sub s}{sup 0}-B{sub s}{sup 0} oscillations from a time-dependent measurement of the B{sub s}{sup 0}-B{sub s}{sup 0} oscillation frequency {delta}m{sub s}. Using a data sample of 1 fb{sup -1} of pp collisions at {radical}(s)=1.96 TeV collected with the CDF II detector at the Fermilab Tevatron, we find signals of 5600 fully reconstructed hadronic B{sub s} decays, 3100 partially reconstructed hadronic B{sub s} decays, and 61 500 partially reconstructed semileptonic B{sub s} decays. We measure the probability as a function of proper decay time that the B{sub s} decays with the same, or opposite, flavor as the flavor at production, and we find a signal for B{sub s}{sup 0}-B{sub s}{sup 0} oscillations. The probability that random fluctuations could produce a comparable signal is 8x10{sup -8}, which exceeds 5{sigma} significance. We measure {delta}m{sub s}=17.77{+-}0.10(stat){+-}0.07(syst) ps{sup -1} and extract vertical bar V{sub td}/V{sub ts} vertical bar =0.2060{+-}0.0007({delta}m{sub s}){sub -0.0060}{sup +0.0081}({delta}m{sub d}+theor)