Measurement of the Bs0-Bs0 oscillation frequency.

We present the first precise measurement of the Bs0-B̄s0 oscillation frequency Δms. We use 1fb-1 of data from pp̄ collisions at s=1.96TeV collected with the CDF II detector at the Fermilab Tevatron. The sample contains signals of 3600 fully reconstructed hadronic Bs decays and 37000 partially reconstructed semileptonic Bs decays. We measure the probability as a function of proper decay time that the Bs decays with the same, or opposite, flavor as the flavor at production, and we find a signal consistent with Bs0-B̄s0 oscillations. The probability that random fluctuations could produce a comparable signal is 0.2%. Under the hypothesis that the signal is due to Bs0-B̄s0 oscillations, we measure Δms=17.31-0.18+0.33(stat)±0. 07(syst)ps-1 and determine |Vtd/Vts|=0.208-0.002+0.001(expt)-0.006+0.008(theor). © 2006 The American Physical Society.