B Physics from lattice simulations

Abstract

In this thesis we present four main results:

The computation of the matching coefficients for a complete set of 4-quark operators between the continuum HQET and Lattice HQET. This result extends and completes a preceding computation of the matching coefficients relevant for the B⁰ - B̄;⁰ mixing (and corrects a mistake in the latter).The Lattice evaluation of the coupling g_B*Bπ, which is related to the form factor of zero momentum transfer of the axial current between B^*- and B-states. Moreover we show how this coupling constant is also related to the coupling g between heavy mesons and low-momentum pions that appears the effect heavy meson chiral Lagrangian. We find the value g = 0.42(4)(8). Besides its theoretical interest, the phenomenological implications of such a determination are discussed.The lattice evaluation of the matrix elements of the four-quark operators which contribute to the lifetimes of B-mesons and the Λ_b-baryon. We find that the spectator effects are larger than naively expected and are in part responsible for the discrepancy between the O(1/m²_b) theoretical prediction and experimental measurement of the ratio of lifetimes τ(Λ_b)/τ(B⁰). In fact for this ratio we obtain the value 0.93(1)(2).A re-evaluation of the B_B parameter relevant for the B⁰ - B̄;⁰ mixing, using our correct result for the matching coefficients. We obtain B_B = 0.96(3).

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