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The phenomenon of CP-violation in weak interactions, discovered in 1964 in decays of neutral kaons, receives a simple and elegant explanation in the Standard Model with three generations of quarks. Indeed, in this model the common source of CP-asymmetry phenomena is represented by a simple complex phase in the unitary matrix (the Cabibbo-Kobayashi-Maskawa matrix) describing the charged weak couplings of the quarks. This simple scheme has never received an accurate validation, because the phenomenological parameters determined from measurements of CP-violation in kaons decays are related to the fundamental parameters of the theory in a complex way, sensitive to large theoretical uncertainties. On the contrary, decays of neutral B mesons like B{sup 0} {yields} J/{psi} K{sub S}{sup 0} represent a unique laboratory to test the predictions of the theory because they are expected to show significant CP-violation effects, the magnitude of which is cleanly related to the Standard Model parameters. Thus experimental facilities have been built with the purpose of performing extensive studies of B decays. The BABAR experiment is operating at one of these facilities, at the Stanford Linear Accelerator Center. It is collecting data at the PEP-II asymmetric e{sup +}e{sup -} collider (E{sub e{sup -}} = 9.0 GeV; E{sub e{sup +}} = 3.1 GeV), a high-luminosity accelerator machine (L = 3 x 10{sup 33} cm{sup -2}s{sup -1}). The center-of-mass energy (10.58 GeV) of the e{sup +}e{sup -} system at PEP-II allows resonant production of the {Upsilon}(4S), a b{bar b} bound state, which decays almost exclusively in a B{sup 0}{bar B}{sup 0} or a B{sup +}B{sup -} pair. A high-acceptance detector, projected and built by a wide international collaboration, detects and characterizes the decay products of the B mesons. From the analysis of the data collected during the first two years of operation, the BABAR collaboration has established CP-violation in decays of neutral B mesons at the 4.1{sigma} level. Besides the primary goal of CP-violation studies, the high luminosity of PEP-II, coupled with the high acceptance of the BABAR detector, allows competitive studies of the properties of a wide set of B decay modes. In particular, measurements of non-leptonic decays are extremely useful to understand the dynamics of the non-perturbative strong interactions involved in these processes. In this thesis a study of the non-leptonic decay mode B{sup {+-}} {yields} J/{psi}{pi}{sup {+-}} is presented.
The presented study of the radiative electroweak "penguin"--Decay B->K*(892)gamma, proceeding by the b->sgamma "loop"-transition, provides an important test of the Standard Model and a candidate of the search for New Physics. The used data sample has been recorded at the Y(4S) resonance with the BABAR detector at the asymmetric electron-positron- collider PEP-II of the Stanford Linear Accelerator Center (SLAC) in California. The B->K*gamma branching fractions are measured in four K*-decay modes. A search for direct CP-violation in the B->K*gamma mode has also been carried out.
The authors present measurements of branching fractions in the b 2!s{bar s}s penguin-dominated decays B 2![phi]K and B° 2![phi]K° in a sample of approximately 89 million B{bar B} pairs collected by the BABAR detector at the PEP-II asymmetric-energy B-meson Factory at SLAC. They determine [Beta](B+ 2![phi]K+) = (10.0{sub -0.8}{sup +0.9} ± 0.5) x 10−6 and [Beta](B° 2![phi]K°) = (8.4{sub -1.3}{sup +1.5} ± 0.5) x 10−6. Additionally, they measure the CP-violating charge asymmetry [Alpha]{sub CP}(B{sup ±} 2![phi]K{sup ±}) = 0.04 {+-} 0.09 {+-} 0.01, with a 90% confidence-level interval of [-0.10, 0.18], and set an upper limit on the CKM- and color-suppressed decay B+ 2![phi][pi]+, [Beta](B+ 2![phi][pi]+)
The authors present preliminary measurements of branching fractions of the b[yields] s[bar s]s penguin-dominated decays B[sup[+-]][yields][phi]K[sup[+-]] and B[sup 0][yields][phi]K[sup 0] in a sample of approximately 89 million B[bar B] pairs collected by the BABAR detector at the PEP-II asymmetric-energy B-meson Factor at SLAC. They determine[Beta](B[sup[+-]][yields][phi]K[sup[+-]])= (10.0[sub -0.8][sup+0.9](stat.)[+-] 0.5(syst.)) x 10[sup -6] and[Beta](B[sup 0][yields][phi]K[sup 0])= (7.6[sub -1.2][sup+1.3](stat.)[+-] 0.5(syst.)) x 10[sup -6]. Additionally, they measure the charge asymmetry[Alpha][sub CP](B[sup[+-]][yields][phi]K[sup[+-]])= 0.039[+-] 0.086(stat.)[+-] 0.011(syst.) and set an upper limit on the CKM- and color-suppressed decay B[sup[+-]][yields][phi][pi][sup[+-]], [Beta](B[sup[+-]][yields][phi][pi][sup[+-]])
We present preliminary measurements of branching fractions and direct CP violating asymmetries in charmless two-body B decays, obtained with the BABAR detector using a sample of 227M {Upsilon}(4S) {yields} B{bar B} decays. We report the first observation of B{sup 0} {yields} K{sup 0}{bar K}{sup 0} and the first observation of direct CP violation in B{sup 0} {yields} K{sup +}{pi}{sup -} decays.