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.

Eine Suche nach dem Zerfall B → π τ ν wird vorgestellt. Die Suche wird auf dem vollständigen Belle Datensatz durchgeführt, der 772E6 B anti-B Paare beinhaltet, die auf der Y(4s) Resonanz mit Belle Detektor am asymmetrischen e+e- KEKB Beschleuniger gesammelt wurden. Das τ Lepton wird in den Zerfallskanälen τ → e ν ν, τ → μ ν ν, τ → π ν und τ → ρ ν rekonstruiert. Eines der beiden B Mesonen, das Btag, wird mittels eines auf NeuroBayes beruhenden Algorithmus vollständig in einem hadronischen Zerfallskanal rekonstruiert. Der Rest des Kollisionsereignisses beinhaltet genau zwei geladene Spuren im Falle eines Signalzerfalls. Die weitere Trennung zwischen Signal und Untergrund wird mithilfe von Boosted Decision Trees durchgeführt. Ein Fit wird in der Verteilung der Extra Energie im elektromagnetischen Kalorimeter ECL, welche definiert ist als alle Energie die weder vom Btag noch von der rekonstruierten Signalseite stammt, durchgeführt. Kein signifikantes Signal wird beobachtet und ein oberes Limit von Br( B → π τ ν ) < 2.5E-4 basierend auf einem Vertrauensintervall von 90% wird bestimmt. Das Ergebnis ist in guter Übereinstimmung mit der Vorhersage des Standard Modells.

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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&amp;gt;2.0 GeV, s_h^{max}&amp;lt;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&amp;gt;1.9 GeV, \tilde {s}^{max}_{h} &amp;lt; 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.

Master of Science / An analysis of B to pi0 l nu and B to eta l nu decays using the neutrino reconstruction technique is presented. The dataset consists of 535 million BB pairs in 492 fb^−1 of data collected with the Belle detector at the KEKB asymmetric e+e− collider. The measured B to pi0 l nu and B to eta l nu branching fractions are B(B to pi0 l nu) = (0.68 ± 0.09 ± 0.11 ± 0.04)×10^−4 and B(B to eta l nu) = (0.42 ± 0.13)×10^−4. The errors on the pi0 measurement are statistical, experimental systematic, and due to b to u l nu modelling, respectively; that on the eta is statistical only. The B to pi0 l nu branching fraction is measured in three q^2 bins: q^2 < 8 GeV^2, 8 GeV^2 ≤ q^2 < 16 GeV^2, and 16 GeV^2 ≤ q^2. The Cabibbo-Kobayashi-Maskawa quark-mixing matrix element |Vub| is extracted from the B to pi0 l nu branching fraction using a Light-Cone Sum Rules form factor extrapolated to the full q^2 range, and is found to be |Vub| = (3.29 ± 0.23 ± 0.27 ± 0.05)×10^−3, where the errors are statistical, experimental systematic, and theoretical, respectively.

Master of Science / An analysis of B to pi0 l nu and B to eta l nu decays using the neutrino reconstruction technique is presented. The dataset consists of 535 million BB pairs in 492 fb^−1 of data collected with the Belle detector at the KEKB asymmetric e+e− collider. The measured B to pi0 l nu and B to eta l nu branching fractions are B(B to pi0 l nu) = (0.68 ± 0.09 ± 0.11 ± 0.04)×10^−4 and B(B to eta l nu) = (0.42 ± 0.13)×10^−4. The errors on the pi0 measurement are statistical, experimental systematic, and due to b to u l nu modelling, respectively; that on the eta is statistical only. The B to pi0 l nu branching fraction is measured in three q^2 bins: q^2 < 8 GeV^2, 8 GeV^2 ≤ q^2 < 16 GeV^2, and 16 GeV^2 ≤ q^2. The Cabibbo-Kobayashi-Maskawa quark-mixing matrix element |Vub| is extracted from the B to pi0 l nu branching fraction using a Light-Cone Sum Rules form factor extrapolated to the full q^2 range, and is found to be |Vub| = (3.29 ± 0.23 ± 0.27 ± 0.05)×10^−3, where the errors are statistical, experimental systematic, and theoretical, respectively.