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.

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.

Diese Studie stellt die Messung des Wirkungsquerschnitts der elektroschwachen Einzel-Top-Quark-Produktion im t-Kanal vor, bei der das Top-Quark semileptonisch zerfällt. Die Studie basiert auf 4.7 fb^{-1} an Daten aus Proton-Proton-Kollisionen, die vom ATLAS-Detektor am Large Hadron Collider im Jahr 2011 aufgezeichnet wurden. Die ausgewählten Ereignisse beinhalten zwei hochenergetische Jets, von denen einer als von einem b-Quark stammend identifiziert wurde, sowie ein hochenergetisches Elektron oder Myon und fehlende Transversalenergie. Der Fall von drei und vier Jets wird ebenfalls betrachtet, aber schließlich verworfen, da ihre Miteinbeziehung die Präzision des Ergebnisses herabsetzt. Die Ereignisrekonstruktion erfolgt durch einen Chi-Quadrat-basierten kinematischen Fit mit W-Boson- und Top-Quark-Massenzwangsbedingungen. Der Wert des Chi-Quadrat in jedem Ereignis dient dazu, das Ereignis als signal- oder untergrundähnlich zu klassifizieren. Der Wirkungsquerschnitt wird mittels eines template-basierten Maximum-Likelihood-Fits an die Verteilung, die die beste Trennschärfe besitzt, extrahiert: Die Verteilung is derart gewählt, dass die Formunterschiede zwischen Signal und Untergrund bezüglich der Kinematik des typischen leichten Vorwärtsjets des t-Kanals ausgenutzt werden. Eine Beobachtung des Single-Top-t-Kanal-Prozesses mit einer Signifikanz von 5.7 Sigma wird erreicht, und der Wirkungsquerschnitt wird zu 111^{+29}_{-28} pb gemessen. Unter der Annahme |Vtb|^{2} >> |Vtd|^{2} + |Vts|^{2} sowie einer (V-A)-, CP-erhaltenden Wechselwirkung, und unter Berücksichtigung von möglichen anomalen Kopplungen am W-t-b-Vertex, wird der Wert des entsprechenden CKM-Matrixelements mal einem anomalen Formfaktor zu |Vtb*f^{L}_{1}| = 1.30^{+0.13}_{-0.16} bestimmt. Dies führt zu einer unteren Grenze im Standardmodell-Szenario 0 / This study presents the cross-section measurement of electroweak single-top quark production in the t-channel with a semi-leptonically decaying top quark. The study is based on 4.7 fb^{-1} of proton-proton collision data recorded with the ATLAS detector at the Large Hadron Collider in the year 2011. Selected events contain two highly energetic jets, one of which is identified as originating from a beauty quark, as well as a highly energetic electron or muon and transverse missing energy. The case of three and four jets is also considered but eventually discarded since their inclusion degrades the precision of the result. The event reconstruction is done with a chi-square-based kinematic fit using W boson and top quark mass constraints. The chi-square value in each event serves to classify the event as a signal-like or background-like process. The cross-section is extracted by performing a template-based maximum likelihood fit to the distribution that displays the best discriminatory power: This distribution is chosen such that the shape differences between signal and background with respect to the typical forward light jet kinematics of the t-channel are exploited. An observation of the single-top t-channel process with a significance of 5.7 Sigma is obtained, and the cross-section is measured to be 111^{+29}_{-28} pb. Assuming |Vtb|^{2} >> |Vtd|^{2} + |Vts|^{2} as well as a (V-A), CP-conserving interaction, and allowing for the presence of anomalous couplings at the W-t-b vertex, the associated value of the CKM matrix element times an anomalous form factor is determined as |Vtb*f^{L}_{1}| = 1.30^{+0.13}_{-0.16}. The corresponding lower limit in the standard model scenario 0