Observation of Bs0 - B̄s0 oscillations

Abstract

We report the observation of Bs0- B̄s0 oscillations from a time-dependent measurement of the Bs0-B̄s0 oscillation frequency Δms. Using a data sample of 1 fb-1 of pp collisions at √ = 1.96 TeV 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 Bs decays, and 61500 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 for Bs0-B̄s0 oscillations. The probability that random fluctuations could produce a comparable signal is 8 × 10-8, which exceeds 5σ significance. We measure Δms = 17.77 ± 0.10(stat) ± 0.07(syst) ps-1 and extract |Vtd/Vts| = 0.2060 ± 0.0007(Δms)-0.0060+0.0081 (Δmd + theor). © 2006 The American Physical Society.