This thesis presents an analysis of inclusive semileptonic $B \to X_u e \nu$ decays using approximately 454 million $\Upsilon(4S) \to B \bar{B}$ decays collected during the years 1999 to 2008 with the BABAR detector. The electron energy, $E_e$, and the invariant mass squared of the electron-neutrino pair,$ q^2$, are reconstructed, where the neutrino kinematics is deduced from the decay products of both B mesons. The final hadronic state,$ X_u$, consists of a sum of many hadronic channels, each of which contains at least one $u$ quark. The variables $q^2$ and $E_e$ are then combined to compute the maximum kinematically allowed invariant mass squared of the hadronic system, $s_h^{max}$. Using these kinematic quantities, the partial branching fraction, $\Delta BR(B \to X_u e \nu)$, unfolded for detector effects, is measured to be $\Delta BR(E_e>2.0 GeV, s_h^{max}<3.52 GeV^2) = (3.33 \pm 0.18 \pm 0.21) \times 10^{-4} in the $\Upsilon(4S)$ and \Delta \tilde{\BR}(\tilde E_e>1.9 GeV, \tilde {s}^{max}_{h} < 3.5 GeV^2) = (4.57 \pm 0.24 \pm 0.32) \times 10^{-4} in the $B$ meson rest frames. The quoted errors are statistical and systematic, respectively. The CKM matrix element $|V_{ub}|$ is determined from the measured $\Delta \tilde{\BR}$ using theoretical calculation based on Heavy Quark Expansion. The result is $|V_{ub}| = (4.19 \pm 0.18{}^{+0.26}_{-0.20} {}^{+0.26}_{-0.25}) \times 10^{-3}, where the errors represent experimental uncertainties, uncertainties from HQE parameters and theoretical uncertainties, respectively.

In dieser Arbeit wird die Messung zweier fundamentaler Parameter des Standardmodells der Teilchenphysik diskutiert: der Betrag des CKM Matrixelements Vcb und die b-Quarkmasse. / In this work, the preliminary measurements of two fundamental parameters of the Standard Model of particles physics are presented: the CKM matrix element Vcb, and the b-quark mass.

Ein Algorithmus zur Identifizierung von Elektronen mit dem BABAR Detektor wird entwickelt. Basierend auf Spuren, deren Teilchenidentität aus rein kinematischen Überlegungen gefolgert werden kann, wird für Impulse zwischen 0.5 und 2.5 GeV/c die Selektionseffizienz für Elektronen zu 90% bestimmt. Im gleichen Impulsbereich liegt die Wahrscheinlichkeit, Pionen als Elektronen zu identifizieren, zwischen 0.05% und 0.1%. Auf diesem Algorithmus basiert die Messung des inklusiven Elektronen Impulsspektrums aus B-Meson Zerfällen anhand der Daten, die mit dem BABAR Detector am asymmetrischen Speicherring PEP-II ("B-Factory") aufgezeichnet wurden. Das Volumen der analysierten Daten entspricht einer integrierten Luminosität von 4.13 1/fb auf der Y(4S) Resonanz und 0.97 1/fb bei einer um 40 MeV verringerten Schwerpunktsenergie. B - Anti-B Ereignisse werden anhand hochenergetischer Elektronen identifiziert. Elektronen von einem semileptonischen Zerfall des zweiten B-Mesons werden durch die relative Ladung und Impulsrichtung zum hochenergetischen Elektron vom Untergrund aus semileptonischen Charm Zerfällen isoliert. Das inklusive Verzweigungsverhältnis für den semileptonischen Zerfall des B-Mesons wird zu (10.85 +-0.22(stat.) +-0.34(sys))% gemessen. Zusammen mit der Lebenszeit von B-Mesonen lässt sich daraus |V_cb| bestimmen: |V_{cb}| = 0.0406 +-0.0009(exp) +-0.0019(theory). / An algorithm for identification of electrons with the BABAR detector is developed. Based on pure samples of electrons and hadrons obtained from data, we determine the electron identification efficiency to be above 90% for momenta above 0.5 GeV/c in the laboratory frame, while the pion fake rate lies between 0.05% and 0.1%. Based on this algorithm, a measurement of the inclusive lepton momentum spectrum in B meson decays is performed. We analyze 4.13 fb^-1 and 0.97 fb^-1 of data recorded at and slightly below the Upsilon(4S) resonance with the BABAR detector at the PEP-II a symmetric B-Factory. B-Bbar events are tagged by a high momentum electron. Using charge and angular correlations, leptons from a second semileptonic $B$ decay are separated from secondary charm semileptonic decays. The inclusive branching ratio is measured to be (10.85 +-0.22(stat.) +-0.34(sys))% . Combined with the B lifetime we determine |V_cb| = 0.0406 +-0.0009(exp) +-0.0019(theory).

Ein Algorithmus zur Identifizierung von Elektronen mit dem BABAR Detektor wird entwickelt. Basierend auf Spuren, deren Teilchenidentität aus rein kinematischen Überlegungen gefolgert werden kann, wird für Impulse zwischen 0.5 und 2.5 GeV/c die Selektionseffizienz für Elektronen zu 90% bestimmt. Im gleichen Impulsbereich liegt die Wahrscheinlichkeit, Pionen als Elektronen zu identifizieren, zwischen 0.05% und 0.1%. Auf diesem Algorithmus basiert die Messung des inklusiven Elektronen Impulsspektrums aus B-Meson Zerfällen anhand der Daten, die mit dem BABAR Detector am asymmetrischen Speicherring PEP-II ("B-Factory") aufgezeichnet wurden. Das Volumen der analysierten Daten entspricht einer integrierten Luminosität von 4.13 1/fb auf der Y(4S) Resonanz und 0.97 1/fb bei einer um 40 MeV verringerten Schwerpunktsenergie. B - Anti-B Ereignisse werden anhand hochenergetischer Elektronen identifiziert. Elektronen von einem semileptonischen Zerfall des zweiten B-Mesons werden durch die relative Ladung und Impulsrichtung zum hochenergetischen Elektron vom Untergrund aus semileptonischen Charm Zerfällen isoliert. Das inklusive Verzweigungsverhältnis für den semileptonischen Zerfall des B-Mesons wird zu (10.85 +-0.22(stat.) +-0.34(sys))% gemessen. Zusammen mit der Lebenszeit von B-Mesonen lässt sich daraus |V_cb| bestimmen: |V_{cb}| = 0.0406 +-0.0009(exp) +-0.0019(theory). / An algorithm for identification of electrons with the BABAR detector is developed. Based on pure samples of electrons and hadrons obtained from data, we determine the electron identification efficiency to be above 90% for momenta above 0.5 GeV/c in the laboratory frame, while the pion fake rate lies between 0.05% and 0.1%. Based on this algorithm, a measurement of the inclusive lepton momentum spectrum in B meson decays is performed. We analyze 4.13 fb^-1 and 0.97 fb^-1 of data recorded at and slightly below the Upsilon(4S) resonance with the BABAR detector at the PEP-II a symmetric B-Factory. B-Bbar events are tagged by a high momentum electron. Using charge and angular correlations, leptons from a second semileptonic $B$ decay are separated from secondary charm semileptonic decays. The inclusive branching ratio is measured to be (10.85 +-0.22(stat.) +-0.34(sys))% . Combined with the B lifetime we determine |V_cb| = 0.0406 +-0.0009(exp) +-0.0019(theory).

As a part of our program to test the unitarity of the Cabibbo-Kobayashi-Maskawa matrix, the decay of the superallowed 0⁺ --> 0⁺ beta emitters ³⁸Ca and ⁴⁶V has been studied in this dissertation. For ³⁸Ca, the half-life, 443.88(36) ms, and superallowed branching ratio, 0.7738(41), have been measured. In our half-life experiment, pure sources of ³⁸Ca were produced and the decay positrons detected in a high-efficiency 4[pi] proportional gas counter. Since the beta⁺ decay of ³⁸Ca feeds ³⁸K^m, which is itself a superallowed beta⁺ emitter, the data were analyzed as a linked parent-daughter decay. Our result for the half-life of ³⁸Ca, with a precision of 0.08%, is a factor of five improvement on the best previous result. The branching-ratio of ³⁸Ca depended on beta-delayed gamma-ray intensities being measured with a high-purity germanium detector calibrated for absolute efficiency to 0.2% precision. This branching-ratio result represents our first step in bringing the ft value for the superallowed ³⁸Ca transition into the desired range of 0.1%. With our half-life and superallowed branching ratio results for ³⁸Ca, we obtain the Ft to be 3072(17) s, in good agreement with the conserved vector current expectation. The half-life of ⁴⁶V has been measured to be 422.66(6) ms, a factor of two more precise than the best previous measurement. Our present result determines the corresponding Ft value to be 3074.5(26) s, which is consistent with the average $\overline{\mathcal{F}t}$ value of 3072.08(79) s established from the 13 best-known superallowed transitions. This demonstrates that previously accepted half-lives of ⁴⁶V were correct in their contribution to a precision test of the conserved vector current hypothesis.

We use a global fit to determine the form factor slopes and branching fractions of the decays B --> Dlnu and B --> D*lnu. We reconstruct Dl pairs and construct a 3-dimensional distribution binned in lepton momentum, D momentum and cosTheta(B-Dl). These kinematic variables provide good separation between the signal and background. We fit electron and muon samples separately and combine them after calculating systematic uncertainties. The form factor slopes, rhoD^2 for B --> Dlnu and rho^2 for B --> D*lnu decays, are measured to be rhoD^2 = 1.22 +- 0.04 +- 0.07 and rho^2 = 1.21 +- 0.02 +- 0.07, where the errors are statistical and systematic, respectively. Branching fractions are fitted to be B(B+ --> D0lnu) = (2.36 +- 0.03 +- 0.12) % and B(B^+ --> D*0lnu) = (5.37 +- 0.02 +- 0.21) %. We use these results to determine the products, G(1)|Vcb| = (43.8 +- 0.8 +- 2.3)*10^{-3} and F(1)|Vcb| = (35.7 +- 0.2 +- 1.2)*10^{-3} of the form factors at zero recoil and the CKM matrix element |Vcb|, from which |Vcb| can be extracted using theoretical input.

Using data collected with the BABAR detector at the SLAC PEP-II electron-positron storage ring operating at a centre-of-mass energy near 10.58 GeV, the branching fractions $B(\tau^- \to \pi^-\pi^-\pi^+\nu_\tau) =(8.83\pm0.01\pm0.13)\%$, $B(\tau^- \to K^-\pi^-\pi^+\nu_\tau) =(0.273\pm0.002 \pm 0.009)\%$, $B(\tau^- \to K^-\pi^-K^+\nu_\tau) =(0.1346 \pm 0.0010 \pm 0.0036)\%$, and $B(\tau^- \to K^-K^-K^+\nu_\tau) =(1.58 \pm 0.13 \pm 0.12)\times10^{-5}$ are measured where the uncertainties are statistical and systematic, respectively. The invariant mass distribution for the $\tau^- \to \pi^-\pi^-\pi^+\nu_\tau$, $\tau^- \to K^-\pi^-\pi^+\nu_\tau$, $\tau^- \to K^-\pi^-K^+\nu_\tau$, and $\tau^- \to K^-K^-K^+\nu_\tau$ decays are unfolded to correct for detector effects. A measurement of $B(\tau^- \to \phi\pi^-\nu_\tau)=(3.42\pm0.55\pm0.25)\times10^{−5}$, a measurement of $B(\tau^- \to \phi^-K^-\nu_\tau) =(3.39\pm0.20\pm0.28)\times10^{−5}$ and an upper limit on $B(\tau^- \to K^-K^-K^+\nu_\tau [ex.\phi]) < =2.5\times10^{−6}$@90\%CL are determined from a binned maximum likelihood fit of the $\tau^- \to K^-\pi^-K^+\nu_\tau$ and $\tau^- \to K^-K^-K^+\nu_\tau$ $K^+K^−$ invariant mass distributions. The branching ratio $B(\tau^- \to K^-\nu_\tau)/B(\tau^- \to\pi^-\nu_\tau)$ is measured to be $(6.531\pm0.056\pm0.093)\times10^{−2}$ from which $|V_{us}|$ is determined to be $0.2255 \pm 0.0023$. The branching ratio $B(\tau^- \to \mu^-\nu_\tau\bar{\nu}_\mu)/B(\tau^- \to e^-\nu_\tau\bar{\nu}_e) =(9.796 \pm 0.016 \pm 0.035)\times10^{−1}$ is measured enabling a precision test of the Standard Model assumption of charged current lepton universality, $g_{\mu}/g_{e}=1.0036 \pm 0.0020$. The branching ratios $B(\tau^- \to K^-\nu_\tau)/B(\tau^- \to e^-\nu_\tau\bar{\nu}_e)=(3.882 \pm 0.032 \pm 0.056)\times10^{−2}$, and $B(\tau^- \to\pi^-\nu_\tau)/B(\tau^- \to e^-\nu_\tau\bar{\nu}_e)=(5.945 \pm 0.014 \pm 0.061)\times10^{−1}$ are measured which provide additional tests of charged current lepton universality, $(g_{\tau}/g_{\mu})_{\pi}= 0.9856 \pm 0.0057$ and $(g_{\tau}/g_{\mu})_{K}= 0.9827 \pm 0.0086$ which can be combined to give $(g_{\tau}/g_{\mu})_{\pi/K}= 0.9850 \pm 0.0054$. Any deviation of these measurements from the expected Standard Model values would be an indication of new physics.

We use a global fit to determine the form factor slopes and branching fractions of the decays B --> Dlnu and B --> D*lnu. We reconstruct Dl pairs and construct a 3-dimensional distribution binned in lepton momentum, D momentum and cosTheta(B-Dl). These kinematic variables provide good separation between the signal and background. We fit electron and muon samples separately and combine them after calculating systematic uncertainties. The form factor slopes, rhoD^2 for B --> Dlnu and rho^2 for B --> D*lnu decays, are measured to be rhoD^2 = 1.22 +- 0.04 +- 0.07 and rho^2 = 1.21 +- 0.02 +- 0.07, where the errors are statistical and systematic, respectively. Branching fractions are fitted to be B(B+ --> D0lnu) = (2.36 +- 0.03 +- 0.12) % and B(B^+ --> D*0lnu) = (5.37 +- 0.02 +- 0.21) %. We use these results to determine the products, G(1)|Vcb| = (43.8 +- 0.8 +- 2.3)*10^{-3} and F(1)|Vcb| = (35.7 +- 0.2 +- 1.2)*10^{-3} of the form factors at zero recoil and the CKM matrix element |Vcb|, from which |Vcb| can be extracted using theoretical input.

Using data collected with the BABAR detector at the SLAC PEP-II electron-positron storage ring operating at a centre-of-mass energy near 10.58 GeV, the branching fractions $B(\tau^- \to \pi^-\pi^-\pi^+\nu_\tau) =(8.83\pm0.01\pm0.13)\%$, $B(\tau^- \to K^-\pi^-\pi^+\nu_\tau) =(0.273\pm0.002 \pm 0.009)\%$, $B(\tau^- \to K^-\pi^-K^+\nu_\tau) =(0.1346 \pm 0.0010 \pm 0.0036)\%$, and $B(\tau^- \to K^-K^-K^+\nu_\tau) =(1.58 \pm 0.13 \pm 0.12)\times10^{-5}$ are measured where the uncertainties are statistical and systematic, respectively. The invariant mass distribution for the $\tau^- \to \pi^-\pi^-\pi^+\nu_\tau$, $\tau^- \to K^-\pi^-\pi^+\nu_\tau$, $\tau^- \to K^-\pi^-K^+\nu_\tau$, and $\tau^- \to K^-K^-K^+\nu_\tau$ decays are unfolded to correct for detector effects. A measurement of $B(\tau^- \to \phi\pi^-\nu_\tau)=(3.42\pm0.55\pm0.25)\times10^{−5}$, a measurement of $B(\tau^- \to \phi^-K^-\nu_\tau) =(3.39\pm0.20\pm0.28)\times10^{−5}$ and an upper limit on $B(\tau^- \to K^-K^-K^+\nu_\tau [ex.\phi]) < =2.5\times10^{−6}$@90\%CL are determined from a binned maximum likelihood fit of the $\tau^- \to K^-\pi^-K^+\nu_\tau$ and $\tau^- \to K^-K^-K^+\nu_\tau$ $K^+K^−$ invariant mass distributions. The branching ratio $B(\tau^- \to K^-\nu_\tau)/B(\tau^- \to\pi^-\nu_\tau)$ is measured to be $(6.531\pm0.056\pm0.093)\times10^{−2}$ from which $|V_{us}|$ is determined to be $0.2255 \pm 0.0023$. The branching ratio $B(\tau^- \to \mu^-\nu_\tau\bar{\nu}_\mu)/B(\tau^- \to e^-\nu_\tau\bar{\nu}_e) =(9.796 \pm 0.016 \pm 0.035)\times10^{−1}$ is measured enabling a precision test of the Standard Model assumption of charged current lepton universality, $g_{\mu}/g_{e}=1.0036 \pm 0.0020$. The branching ratios $B(\tau^- \to K^-\nu_\tau)/B(\tau^- \to e^-\nu_\tau\bar{\nu}_e)=(3.882 \pm 0.032 \pm 0.056)\times10^{−2}$, and $B(\tau^- \to\pi^-\nu_\tau)/B(\tau^- \to e^-\nu_\tau\bar{\nu}_e)=(5.945 \pm 0.014 \pm 0.061)\times10^{−1}$ are measured which provide additional tests of charged current lepton universality, $(g_{\tau}/g_{\mu})_{\pi}= 0.9856 \pm 0.0057$ and $(g_{\tau}/g_{\mu})_{K}= 0.9827 \pm 0.0086$ which can be combined to give $(g_{\tau}/g_{\mu})_{\pi/K}= 0.9850 \pm 0.0054$. Any deviation of these measurements from the expected Standard Model values would be an indication of new physics.

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