The authors report the measurement of the branching fractions of the rare decays B° → D{sub s}{sup (*)+}?−, B° → D{sub s}{sup (*)+}?−, and B° → D{sub s}{sup (*)-} K{sup (*)+} in a sample of 381 x 106?(4S) decays into B{bar B} pairs collected with the BABAR detector at the PEP-II asymmetric-energy ee− storage ring. They present evidence for the decay B° → D{sub s}− K*+ and the vector-vector decays B° → D{sub s}{sup *+}?− and B° → D{sub s}{sup *-} K{sup *+}, as well as the first measurement of the vector meson polarization in these decays. They also determine the ratios of the CM-suppressed to CKM-favored amplitudes r(D{sup (*)}?) and r(D{sup (*)}?) in decays B° → D{sup (*)}{sup {+-}}?{sup {-+}} and B° → D{sup (*)}{sup {+-}}?{sup {-+}}, and comment on the prospects for measuring the Cp observable sin(2? +?).

This 2nd edition is an extensive update of "B Decays?. The revisions are necessary because of the extensive amount of new data and new theoretical ideas. This book reviews what is known about b-quark decays and also looks at what can be learned in the future.The importance of this research area is increasing, as evidenced by the approval of the luminosity upgrade for CESR and the asymmetric B factories at SLAC and KEK, and the possibility of experiments at hadron colliders.The key experimental observations made thus far, measurement of the lifetimes of the different B species, B0-B0 mixing, the discovery of ?Penguin? mediated decays, and the extraction of the CKM matrix elements Vub and Vcb from semileptonic decays, as well as more mundane results, are described in great detail by the experimentalists who have been closely involved with making the measurements. Theoretical progress in understanding b-quark decays using HQET and lattice gauge techniques are described by theorists who have developed and used these techniques.Synthesizing the experimental and theoretical information, several articles discuss the implications for the ?Standard Model? and how further tests can be done using measurements of CP violation in the B system.

We present a measurement of the branching fraction of neutral B meson decaying to final states containing a K1 meson, i.e. K1(1270) and K1(1400), and a charged pion. The data, collected with the BABAR detector at the Stanford Linear Accelerator Center, represent 454 million B{bar B} pairs produced in ee− annihilation. We measure the branching fraction?(B° → K1+?−) = (31.0 ± 2.7 ± 6.9) x 10−6, where the first error quoted is statistical and the second is systematic. In the framework of the K-matrix formalism used to describe these decays, we also set limits on the ratio of the production constants for the K1(1270)+ and K1(1400)+ mesons in B° decays.

This thesis describes the measurement of the branching fractions of the suppressed charmed B0 → D*- a0+ decays and the non-resonant B0 → D*- [eta][pi]+ decays in approximately 230 million [Upsilon](4S) → B$\bar{B}$ events. The data have been collected with the BABAR detector at the PEP-II B factory at the Stanford Linear Accelerator Center in California. Theoretical predictions of the branching fraction of the B0 → D*- a0+ decays show large QCD model dependent uncertainties. Non-factorizing terms, in the naive factorization model, that can be calculated by QCD factorizing models have a large impact on the branching fraction of these decay modes. The predictions of the branching fractions are of the order of 10-6. The measurement of the branching fraction gives more insight into the theoretical models. In general a better understanding of QCD models will be necessary to conduct weak interaction physics at the next level. The presence of CP violation in electroweak interactions allows the differentiation between matter and antimatter in the laws of physics. In the Standard Model, CP violation is incorporated in the CKM matrix that describes the weak interaction between quarks. Relations amongst the CKM matrix elements are used to present the two relevant parameters as the apex of a triangle (Unitarity Triangle) in a complex plane. The over-constraining of the CKM triangle by experimental measurements is an important test of the Standard Model. At this moment no stringent direct measurements of the CKM angle [gamma], one of the interior angles of the Unitarity Triangle, are available. The measurement of the angle [gamma] can be performed using the decays of neutral B mesons. The B0 → D*- a0+ decay is sensitive to the angle [gamma] and, in comparison to the current decays that are being employed, could significantly enhance the measurement of this angle. However, the low expected branching fraction for the B0 → D*- a0+ decay channels could severely impact the measurement. A prerequisite of the measurement of the CKM angle is the observation of the B0 → D*- a0+ decay on which this thesis reports. The BABAR experiment consists of the BABAR detector and the PEP-II e+e- collider. The design of the experiment has been optimized for the study of CP violation in the decays of neutral B mesons but is also highly suitable for the search for rare B decays such as the B0 → D*- a0+ decay. The PEP-II collider operates at the [Upsilon](4S) resonance and is a clean source of B$\bar{B}$ meson pairs.