Observation of Bs0-B¯s0 Oscillations

We report the observation of B_s⁰-B¯_s⁰ oscillations from a time-dependent measurement of the B_s⁰-B¯_s⁰ oscillation frequency Δm_s. Using a data sample of 1fb^-1 of pp¯ collisions at s=1.96TeV collected with the CDF II detector at the Fermilab Tevatron, we find signals of 5600 fully reconstructed hadronic B_s decays, 3100 partially reconstructed hadronic B_s decays, and 61 500 partially reconstructed semileptonic B_s decays. We measure the probability as a function of proper decay time that the B_s decays with the same, or opposite, flavor as the flavor at production, and we find a signal for B_s⁰-B¯_s⁰ oscillations. The probability that random fluctuations could produce a comparable signal is 8×10^-8, which exceeds 5σ significance. We measure Δm_s=17.77±0.10(stat)±0.07(syst)ps^-1 and extract |V_td/V_ts|=0.2060±0.0007(Δm_s)_-0.0060^+0.0081(Δm_d+theor).