Rare Decays in BaBar: Search for Decays of the Neutral B Meson into Two Leptons and Measurement of CP Asymmetry in Inclusive Radiative Decays of the B Meson into a Strange-quark System

Abstract

The purpose of this thesis is the study of rare decays with the BABAR detector. In the first part we present the study of the leptonic decays B0 → e+e−, B0 → µ+µ− and B0 →e±µ∓, based on a dataset corresponding to (383.6± 4.2)× 106 B ¯B pairs. We do not find evidence of any of the three decay modes, and obtain upper limit on the branching fractions, at 90% confidence level, of BR(B0 → e+e−) < 11.3 × 10−8, BR(B0 →µ+µ−) <5.2×10−8, and BR(B0 → e±µ∓) < 9.2×10−8. In the second part we present the measurement of CP asymmetry in rare inclusive B → Xsγ decays on the recoil of fully-reconstructed hadronic B decays, using a dataset corresponding to (465.0±5.1)×106 B ¯ B pairs. We measure a value of ACP = −0.12 ±0.11±0.03.