Measurement of the B hadron lifetime

This thesis presents an experimental determination of the average B hadron lifetime. B hadrons, particles that contain bottom quarks, are produced from electron-positron collisions in the PEP storage ring at a center of mass energy of 29 GeV. Using data taken by the Mark II detector, the decays of B hadrons are tagged by identifying leptons at high transverse momentum relative to the event axis. By means of a precision inner drift chamber, the impact parameters of these lepton tracks are measured with respect to the B hadron production point. From this impact parameter distribution, the average B hadron lifetime is then deduced. Based on a sample of 617 leptons, this lifetime is found to be: τb = (0.98 ± 0.12 ± 0.13) x 10-12 sec, where the first error is statistical and the second systematic. It is believed that the B hadron lifetime is largely determined by the lifetime of the bottom quark. This thesis therefore presents a measurement of a fundamental property of bottom quark decay via the weak interaction. In addition, in conjunction with other experimental results, this measurement can be used to place constraints on models of quark mixing