I present the results of searches for B meson decays into two charmless mesons. I take into account final states made up of two pseudo-scalar (PP) or one pseudo-scalar and one vector (PV). The measurements use the data samples collected and analyzed by the B-factory experiments at the [Upsilon](4S) resonance energy: BABAR, Belle and CLEO.

We present measurements of the branching fractions, longitudinal polarization, and direct CP-violation asymmetries for the decays B →?°K*+ and B+ f0(980)K*+ with a sample of (467 ± 5) x 106 B{bar B} pairs collected with the BABAR detector at the PEP-II asymmetric-energy e+e− collider at the SLAC National Accelerator Laboratory. We observe B+ →?°K*+ with a significance of 5.3? and measure the branching fraction?(B+ →?°K*+) = (4.6 ± 1.0 ± 0.4) x 10−6, the longitudinal polarization f{sub L} = 0.78 ± 0.12 ± 0.03, and the CP-violation asymmetry A{sub CP} = 0.31 ± 0.13 ± 0.03. We observe B+ → f0(980)K*+ and measure the branching fraction?(B+ → f0(980)K*+) x?(f0(980) →?+?−) = (4.2 ± 0.6 ± 0.3) x 10−6 and the CP-violation asymmetry A{sub CP} = -0.15 ± 0.12 ± 0.03. The first uncertainty quoted is statistical and the second is systematic.

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 authors present preliminary measurements of the branching fraction and the CP-violating charge asymmetry in the B[sup +] --> K[sup 0][pi][sup +] decay, and a preliminary measurement of the branching fraction of the B[sup 0] --> K[sup 0][bar K][sup 0] decay. No evidence of direct CP violation in the B[sup +] --> K[sup 0][pi][sup +] mode is observed. The B[sup 0] --> K[sup 0][bar K][sup 0] measurement constitutes the first observation of this decay channel: the probability of obtaining the result assuming the null-signal hypothesis is 3.4 x 10[sup -6]. The authors have also searched for the B[sup +] --> [bar K][sup 0]K[sup +] decay and set an upper limit on its branching fraction at 2.35 x 10[sup -6] at the 90% C.L. The branching-fraction measurements reported here are consistent with previous measurements of the same quantities, but are extracted from a data sample larger by a factor of 2.6.

The authors report searches for B-meson decays to the charmless final states {rho}K* and f{sub 0}(980)K* with a sample of 232 million B{bar B} pairs collected with the BABAR detector at the PEP-II asymmetric-energy e{sup +}e{sup -} collider at SLAC.

The authors present preliminary measurements of branching fractions of the b 2!s{bar s}s penguin-dominated decays B{sup ±} 2![phi]K{sup ±} 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 Factor at SLAC. They determine [Beta](B{sup ±} 2![phi]K{sup ±}) = (10.0{sub -0.8}{sup +0.9}(stat.) {+-} 0.5(syst.)) x 10−6 and [Beta](B° 2![phi]K°) = (7.6{sub -1.2}{sup +1.3}(stat.) {+-} 0.5(syst.)) x 10−6. Additionally, they measure the charge asymmetry [Alpha]{sub CP}(B{sup {+-}} 2![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 {+-}} 2![phi][pi]{sup {+-}}, [Beta](B{sup {+-}} 2![phi][pi]{sup {+-}})

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]+)