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Recent results at the LHCb and B-factory experiments have suggested that rare processes in B →Vγ and B → V ℓ¯ℓ decays, where V is a vector meson, show some deviation from Standard Model predictions. Although these anomalies are not yet at the level to constitute a formal discovery, they are certainly suggestive of potential New Physics effects in flavour-changing neutral currents. However, explanations within the Standard Model cannot yet be ruled out. This thesis contributes to the understanding of such anomalies in two ways. Firstly, the angular distribution of the B → KJ (→ Kπ)ℓ1¯ℓ2 decay is derived, for the full dimension-six effective weak Hamiltonian, using a generalisation of the helicity formalism to effective theories mediating b → sℓ1¯ℓ2 transitions. This approach sheds light on the origin of the underlying structure, and in the process extends the general angular distribution to decays in which the two leptons in the final state, ℓ1¯ℓ2, are not necessarily identical. An additional benefit of the derivation of the angular distribution presented in this manner is that it lends itself to a moments analysis of the decay. It is shown how the angular distribution changes in the presence of new operators, predicted to be vanishingly small in the Standard Model. Such operators could be sizeable in the presence of New Physics, but using a moments analysis enables the contribution of such operators to be assessed. Secondly, an analysis is presented of the three-particle vector and axial meson distribution amplitudes. It is shown that the distribution amplitudes of both particles are, up to QCD corrections, nearly identical. These results are applied to a new calculation of the long-distance charm loop contribution to radiative B → Vγ decays, and it is shown that the approximate symmetry can be exploited to provide an improved theoretical control in the search for New Physics contributions to right-handed currents in radiative decays.

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.

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.

This thesis presents first measurements of moments of the hadronic n_X^2 distribution measured in inclusive semileptonic decays of B mesons to final states containing a charm quark, B->Xc l nu. The variable n_X^2 is a combination of the invariant mass of the charmed meson m_X, its energy in the B-meson rest-frame E_X, and a constant \tilde{\Lambda} = 0.65 GeV, n_X^2 = m_X^2 c^4 - 2 \tilde{\Lambda} E_X + \tilde{\Lambda}^2. The moments <n_X^k> 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- -> Y(4S) -> 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 n_X^2 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 <n_X^k> up to order k=6 combined with other measurements of moments of the lepton-energy spectrum in decays B->Xc l nu and moments of the photon-energy spectrum in decays B->Xs gamma, we determine the quark-mixing parameter |V_{cb}|, the bottom and charm quark masses, the semileptonic branching fraction BR(B->X l nu), and four non-perturbative heavy quark parameters. Using HQE calculations in the kinetic scheme up to order 1/m_b^3 we find |V_{cb}| = (41.65 +- 0.43 +- 0.40 +- 0.58) x 10^{-3} and m_b = (4.570 \pm 0.033 \pm 0.043)GeV/c^2, where the first uncertainty refers to experimental contributions, the second to uncertainties in the HQE, and the third to theoretical uncertainties in the calculations of the semileptonic decay rate. All obtained results are consistent with previous determinations. The inclusion of the moments <n_X^6> decreases the uncertainty on the HQE parameters mu_{pi} and rho_{D}. Furthermore, the theoretical treatment of higher order corrections in the HQE used for the moments <m_X^k> has been verified with these new measurements.

The branching fraction for B -> rho e nu decays and the CKM matrix element |Vub| is measured with semileptonic exclusive B-meson decays using approximately 55 million Upsilon(4S) -> BBbar decays collected during the years 2000 and 2001 with the BABAR detector. The result is Br(B0 -> rho- e+ nu) = (3.39 +- 0.44 +- 0.52 +- 0.60) x 10^-4, and |Vub| = (3.69 +- 0.23 +- 0.27 +0.40-0.59) x 10^-3. The quoted errors are statistical, systematic, and theoretical respectively. These are combined results obtained using five different form-factor models. Individual results are also quoted. / Das Verzweigungsverhältnis B -> rho e nu und das CKM Matrix Element |Vub| werden mittels semileptonischer exklusiver B Mesonen Zerfälle gemessen. Die Daten wurden in den Jahren 2000 und 2001 mit dem BABAR Dektektor aufgezeichnet und ensprechen ungefähr 55 Millionen Upsilon(4S) -> BBbar Zerfällen. Das Ergebnis ist Br(B0 -> rho- e+ nu) = (3.39 +- 0.44 +- 0.52 +- 0.60) x 10^-4 und |Vub| = (3.69 +- 0.23 +- 0.27 +0.40-0.59) x 10^-3. Die angegebenen Fehler sind statistisch, systematisch und theoretisch. Dieses Ergebnis ist eine Kombination von Ergebnissen fünf verschiedener Form-Faktor Modelle. Die Ergebnisse werden auch für jedes Modell einzeln angegeben.

This thesis presents first measurements of moments of the hadronic n_X^2 distribution measured in inclusive semileptonic decays of B mesons to final states containing a charm quark, B->Xc l nu. The variable n_X^2 is a combination of the invariant mass of the charmed meson m_X, its energy in the B-meson rest-frame E_X, and a constant \tilde{\Lambda} = 0.65 GeV, n_X^2 = m_X^2 c^4 - 2 \tilde{\Lambda} E_X + \tilde{\Lambda}^2. The moments <n_X^k> 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- -> Y(4S) -> 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 n_X^2 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 <n_X^k> up to order k=6 combined with other measurements of moments of the lepton-energy spectrum in decays B->Xc l nu and moments of the photon-energy spectrum in decays B->Xs gamma, we determine the quark-mixing parameter |V_{cb}|, the bottom and charm quark masses, the semileptonic branching fraction BR(B->X l nu), and four non-perturbative heavy quark parameters. Using HQE calculations in the kinetic scheme up to order 1/m_b^3 we find |V_{cb}| = (41.65 +- 0.43 +- 0.40 +- 0.58) x 10^{-3} and m_b = (4.570 \pm 0.033 \pm 0.043)GeV/c^2, where the first uncertainty refers to experimental contributions, the second to uncertainties in the HQE, and the third to theoretical uncertainties in the calculations of the semileptonic decay rate. All obtained results are consistent with previous determinations. The inclusion of the moments <n_X^6> decreases the uncertainty on the HQE parameters mu_{pi} and rho_{D}. Furthermore, the theoretical treatment of higher order corrections in the HQE used for the moments <m_X^k> has been verified with these new measurements.

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.

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.