Limits are set on $B^0$B${¯}^0$ mixing by use of dilepton events from Υ(4S) decay. On the assumption that the charged- and neutral-B semileptonic branching ratios are equal and that 41% of the B mesons from the Υ(4S) are neutral, a 90%-confidence-level upper limit of 24% is set on $B^0$B${¯}^0$ mixing. Limits are also given for the ratio of the lifetimes of neutral and charged B mesons. The 90%-confidence-level limits are &<2.05.

• Received 24 July 1986

DOI:https://doi.org/10.1103/PhysRevLett.58.183