Effective field theory approaches to B meson decay

In this thesis we look at a variety of B meson decays. These decays are important for measuring the CKM matrix elements and over-constraining the standard model. We consider two categories of decays: inclusive semi-leptonic and exclusive non-leptonic.; Inclusive semi-leptonic B¯ → X uℓnuℓ decays are the theoretically cleanest ways to extract the CKM matrix element | Vub|. A large B¯ → Xuℓnu background reduces the available phase space, leaving the decay rate sensitive to the non-perturbative shape function of the B meson. We study the O(Λ QCD/mb) corrections to the hadronic invariant mass spectrum dGamma/dsH in B¯ → Xuℓnu ℓ decays, and discuss the implications for the extraction of |Vub|. Using simple models for the subleading shape functions, the effects of subleading operators are estimated to be at the few percent level for experimentally relevant cuts. The subleading corrections proportional to the leading shape function are larger, but largely cancel in the relation between the hadronic invariant mass spectrum and the photon energy spectrum in B¯ → X sgamma.; For two-body exclusive decays of the form B¯ →pipi, pi K, we study Oa2s b0 perturbative corrections in the QCD factorization formalism, including chirally enhanced power corrections. We discuss the effect of these corrections on direct CP asymmetries, which receive their first contribution at Oas . We find that the Oa2s b0 corrections are often as large as the Oas corrections, and that the scale dependence present at leading order is not reduced by the inclusion of the Oas corrections. In particular we assess the effect of the perturbative corrections on the direct CP violation parameters of B 0 → pi+pi-, which provide an interesting constraint on the unitarity triangle.; Also in the context of QCD factorization, we study two-body exclusive decays of the form B → D(*) L (L = pi, rho, K) in the heavy quark limit. We perform a renormalon analysis of such processes to determine the order at which nonperturbative factorization breaking power corrections enter the amplitude. We find that a class of leading power corrections to the color octet matrix element, of O (ΛQCD/mb), vanish in the limit of a symmetric light meson parton distribution function. We discuss the phenomenological significance of this result.