Observation of Bs-Bs_bar Oscillations with the CDF II Detector

par Alessandro Cerrii (CERN)

lundi 23 oct. 2006, 14:00 → 15:00 Europe/Paris

Amphithéâtre

The CDF collaboration observes Bs - Bs_bar oscillations performing a time-dependent measurement of the oscillation frequency Δms. Using a data sample of 1 fb-1 of p-pbar collisions at sqrt(s) = 1.96 TeV collected with the CDF II detector at the Fermilab Tevatron, we find signals of ~5600 full reconstructed hadronic Bs decays, ~3100 partially reconstructed hadronic Bs decays, and ~61500 partially reconstructed semileptonic Bs decays. We measure the probability as a function or proper decay time the that the Bs decays with the same, or opposite, flavor as the flavor at production, and we find a signal for Bs - Bs_bar oscillations. The probability that random fluctuations could produce a comparable signal is 8x10-8, which exceeds 5σ significance. The measurement of the oscillation frequency yields: Deltam_s=17.77 ± 0.10(stat) ± 0.07(sys) which through lattice QCD yields the most precise determination of Vtd/Vts to date: = 0.2060 ± 0.0007(exp) +0.0081 - 0.0060 (theor)