Two measurements ofB0B¯0mixing

We have measured the ${\mathit{B}}^0$B${\mathrm{¯}}^0$ mixing probability, ${\mathrm{\chi }}_{\mathit{d}}$, using a sample of 965 000 BB¯ pairs from Υ(4S) decays. Counting dilepton events, we find ${\mathrm{\chi }}_{\mathit{d}}$=0.157±0.016±0.${018}_{\mathrm{-}0.021}^{+0.028\mathrm{}}$. Using tagged ${\mathit{B}}^0$ events, we find ${\mathrm{\chi }}_{\mathit{d}}$=0.149±0.023±0.019±0.010. The first (second) error is statistical (systematic). The third error reflects a ±15% uncertainty in the assumption, made in both cases, that charged and neutral B pairs contribute equally to dilepton events. We also obtain a limit on the CP impurity in the ${\mathit{B}}_{\mathit{d}}^0$ system, ‖Re(${\mathrm{\epsilon }}_{\mathit{B}}^0$)‖<0.045 at 90% C.L.