Book Description

In March 2001 the Tevatron accelerator entered its Run II phase, providing colliding proton and anti-proton beams with an unprecedented center-of-mass energy of 1.96 TeV. The Tevatron is currently the only accelerator to produce ?b baryons, which provides a unique opportunity to measure the properties of these particles. This thesis presents a measurement of the mean lifetime of the ?b baryon in the semileptonic channel ?$0top{b}$ → ?$+top{c}$ ?- $ar{v}$?. In total 186 pb-1 of data were used for this analysis, collected with the CDF detector between February 2002 and September 2003. To select the long-lived events from b-decays, the secondary vertex trigger was utilized. This significant addition to the trigger for Run II allows, for the first time, the selection of events with tracks displaced from the primary interaction vertex at the second trigger level. After the application of selection cuts this trigger sample contains approximately 991 ?b candidates. To extract the mean lifetime of ?b baryons from this sample, they transverse decay length of the candidates is fitted with an unbinned maximum likelihood fit under the consideration of the missing neutrino momentum and the bias introduced by the secondary vertex trigger. The mean lifetime of the ?b is measured to be ? = 1.29 ± 0.11(stat.) ± 0.07(syst.) ps equivalent to a mean decay length of c? = 387 ± 33(stat.) ± 21 (syst.) ?m.