Oscillations of neutral B mesons systems

The oscillation phenomenon in the neutral B mesons systems is now well established. The motivations and principles of the measurements are given; then the most recent results from the LEP experiments, the CDF collaboration at Fermilab and the SLD collaboration at SLAC are reviewed. The present world average of the B o d meson oscillation frequency is Δ m d = 0.471 ± 0.016ps −1 and the lower limit on the B o S oscillation frequency is Δ m s > 12.4 ps −1 at 95% CL.