The measurement of the B0 and B± lifetimes

During the 1994 and 1995 data collection runs at LEP over 2.5 million hadronic events were recorded at DELPHI; these yielded over 1 million beauty hadrons of various sub-species. Of these 81,288 were tagged and used to measure the lifetimes of the B± and B0 mesons. The results of these measurements are as follows: TB± = 1.643 ± 0.034 (stat.) ± 0.025 (sys.) ps (1) TB0 = 1.496 ± 0.040 (stat.) -0.029+0.031 (sys.) ps (2). In addition the ratio of the lifetimes of the beauty hadron subspecies were evaluated to be: T± / TB0 = 1.098 ± 0.051 (stat.) ± 0.030 (sys.) (3). From the values of TB± and TB0 the CKM matrix element Vcb was extracted giving the averaged value of: vertical bar Vcb vertical bar = (4.01 ± 0.19(tot.))x10-2 (4) (author)