| The measurement of the lifetime of the B0s meson has great importance and is of special interest. The first motivation is to check the Heavy Quark Expansion (HQE) predictions for the B meson lifetimes. Besides testing HQE, the lifetime of the b quark is directly related to the CKM matrix element Vcb; the B meson lifetime measurement thus gives a good probe of the weak decay mechanics of the heavy hadrons. The B0s meson is of special interest because of the expected B0sB&d1;0 s mixing with large oscillation frequency, which can be expressed in terms of Deltam, the mass difference of the two mass eigenstates of the B0s meson. The B0s mesons contain short and long lived components, the light (L) and heavy (H) eigenstates, BL and BH . They differ not only in their masses Deltam = mL - mH, but also in their widths DeltaGamma = GammaL - Gamma H, which is expected to be large enough to be measurable. In flavor-specific decays, such as the semileptonic decay in this analysis, the B0s will have equal fractions of BL and BH when generated. A superposition of two exponentials thus results with decay width Gammas +/- DeltaGamma s/2. When fitting to a single exponential we obtain a measure of the flavor-specific lifetime: tB0s fs=1Gs 1+DGs/2G s21- DGs/2Gs 2 Hence by measuring tau( B0s )fs, in combination with other measurements, we can reduce the significant correlations between the average B0s lifetime tau( B0s ) = 1Gs and DeltaGammas/Gamma s, and determine them more precisely.;In this dissertation, the lifetime of the B0s meson is measured using partially reconstructed semileptonic decays. The following semileptonic decay processes (and their charge conjugates) are used in this analysis: B0s→l++D- s+X where l denotes either a muon or an electron, and the Ds decays into D-s→f+p -,f→K++K- D-s→K*0 +K-,K*0→K+ +p- D-s→p ++p-+p- .;The data were collected during the years 2002 to 2005 using 4 GeV lepton plus displaced track triggers (lepton+SVT) by the CDF Collaboration at the Fermi National Accelerator Laboratory during Run II of the Tevatron Collider. The corresponding integrated luminosity is approximately 1 fb-1 .;The lepon+SVT triggers select events which contain a muon or an electron with a transverse momentum greater than 4 GeV/c and a displaced track. For these lepton and SVT displaced tracks candidates, further identification requirements are imposed to improve the purity of the B0s semileptonic decay signal.;From the lepton+charm pairs, we measure the B0s meson decay lengths to extract the lifetime. Since the B0s meson momentum, necessary to calculate the B0s decay time, is not fully reconstructed in semileptonic decays, we use Monte Carlo simulation to correct for the missing momentum. The Monte Carlo simulation is also used for determining the ct efficiency curve, which is affected strongly by the displaced track requirement. Contributions from various backgrounds are also considered.;From these data, the B0s meson lifetimes is measured to be ctB0s fs=436.6+/-5.4+/-13.1m m or tB0s fs=1.456+/-0.018+/-0.044p s where the first uncertainty is statistical and the second is systematic, respectively. |
