Measurement of B0−B0 mixing at the CERN Spp̄S collider

Abstract We report on a new measurement of B 0 − B 0 mixing at the CERN SppS collider. Mixing is measured in the non-isolated high mass dimoun sample using data from the 1988–1989 collider runs. The measured value of the mixing parameter, χ , is 0.145±0.035(stat.) ± 0.014(syst.). The average of this measurement and that from our 1984–1985 data is ξ = 0.14 ± 0.029 (stat.) ± 0.017 (syst.) assuming fully correlated errors. Using the measurement of ξ d from ARGUS and CLEO , we obtain χ = 0.50 ± 0.20, which gives a limit of χ s > 0.17 (0.12) at 90% (95%) CL. Including the measurements of χ from the ALEPH and L3 experiments gives χ s = 0.53 ± 0.15, and a limit of χ s > 0.27 (0.23) at 90% (95%) CL.