Using 180 pb−1 of data collected with the CDF II detector at the Tevatron, we measure the first two moments of the hadronic invariant mass-squared distribution in charmed semileptonic B decays. From these we determine the non-perturbative Heavy Quark Effective Theory parameters? and?1 used to relate the B meson semileptonic branching ratio to the CKM matrix element.

We report a measurement of the first four moments of the hadronic mass distribution in {bar B} → X{sub c}l− {bar {nu}} decays. The measurements are based on 89 million [Upsilon](4S) → B{bar B} events where the hadronic decay of one of the B mesons is fully reconstructed and a charged lepton from the decay of the other B meson is identified. The moments are presented for minimum lepton momenta ranging from 0.9 to 1.6 GeV in the B rest frame. It is expected that such measurements will lead to improved determinations of.

This thesis presents first measurements of moments of the hadronic nX2 distribution measured in inclusive semileptonic decays of B mesons to final states containing a charm quark, B 2!Xcl[nu]. The variable nX2 is a combination of the invariant mass of the charmed meson mX, its energy in the B-meson rest-frame EX;BRF, and a constant ~[Lambda] = 0.65 GeV, nX2 = mX2c4-2~[Lambda]EX, BRF + ~[Lambda]2. The moments nXk with k = 2,4,6 are measured as proposed by theory to constrain assumptions made in the theoretical description of inclusive observables in semileptonic B-meson decays. This description uses Heavy Quark Expansion (HQE), an effective QCD combined with an Operator Product Expansion. The measurement is based on a sample of 231.6 million e+e- 2 2!B$\bar{B}$ events recorded with the BABAR experiment at the PEP-II e+e--storage rings at SLAC. We reconstruct the semileptonic decay by identifying a charged lepton in events tagged by a fully reconstructed hadronic decay of the second B meson. Correction procedures are derived from Monte Carlo simulations to ensure an unbiased measurement of the moments of the nX2 distribution. All moments are measured requiring minimum lepton momenta between 0.8 GeV/c and 1.9 GeV/c in the rest frame of the B meson. Performing a simultaneous fit to the measured moments nXk up to order k = 6 combined with other measurements of moments of the lepton-energy spectrum in decays B 2!Xcl[nu] and moments of the photon-energy spectrum in decays B 2!Xs[gamma], we determine the quark-mixing parameter.

We report a preliminary measurement of the first and second moments of the hadronic mass distributions in B → X{sub c}l[nu] decays. The measurements are based on [Upsilon](4S) → B{bar B} events where the hadronic decay of one of the B mesons is fully reconstructed and a charged lepton from the decay of the other B meson is identified. The moments are presented for threshold lepton momenta ranging from 0.9 to 1.6 GeV. From the M{sub X}2 moments we determine the non-perturbative Heavy Quark Expansion (HQE) parameters, {bar {Lambda}} and [lambda]1. We combine the measured moments M{sub X}2 with earlier BABAR measurements of the semileptonic branching ratios and B lifetimes and perform a simultaneous fit to the HQE for the moments obtained for different threshold lepton momenta and the semileptonic decay width. This fit results in an improved value for the CKM matrix element.

This 2nd edition is an extensive update of "B Decays?. The revisions are necessary because of the extensive amount of new data and new theoretical ideas. This book reviews what is known about b-quark decays and also looks at what can be learned in the future.The importance of this research area is increasing, as evidenced by the approval of the luminosity upgrade for CESR and the asymmetric B factories at SLAC and KEK, and the possibility of experiments at hadron colliders.The key experimental observations made thus far, measurement of the lifetimes of the different B species, B0-B0 mixing, the discovery of ?Penguin? mediated decays, and the extraction of the CKM matrix elements Vub and Vcb from semileptonic decays, as well as more mundane results, are described in great detail by the experimentalists who have been closely involved with making the measurements. Theoretical progress in understanding b-quark decays using HQET and lattice gauge techniques are described by theorists who have developed and used these techniques.Synthesizing the experimental and theoretical information, several articles discuss the implications for the ?Standard Model? and how further tests can be done using measurements of CP violation in the B system.

The absolute branching fractions for the decays $D^-_s\rightarrow\ell^-\bar{\nu}_{\ell}$ ($\ell=e$, $\mu$, or $\tau$) are measured using a data sample corresponding to an integrated luminosity of 521 fb$^{-1}$ collected at center of mass energies near 10.58 GeV with the BABAR detector at the PEP-II $e^+e^-$ collider at SLAC. The number of $D_s^-$ mesons is determined by reconstructing the recoiling system $DKX\gamma$ in events of the type $e^+e^-{\rightarrow}DKXD^{*-}_s$, where $D^{*-}_s\rightarrow D^-_s\gamma$ and $X$ represents additional pions from fragmentation. The $D^-_s\rightarrow\ell^-\nu_{\ell}$ events are detected by full or partial reconstruction of the recoiling system $DKX\gamma\ell$. The following results are obtained: $B(D^-_s \to \mu^- \nu) = (6.02 \pm 0.38 \pm 0.34) \times 10^{-3}$, $B(D^-_s \to \tau^- \nu) = (5.00 \pm 0.35 \pm 0.49) \times 10^{-2}$, and $B(D^-_s \to e^- \nu)