| The BABAR detector at the PEP-II asymmetric-energy e+e- collider is located at the Stanford Linear Accelerator Center. It has been gathering data on the Upsilon(4S) resonance from 2000 until 2007 with the primary objective of studying CP violation in B-meson decays. In this thesis we provide a theoretical overview of how CP violation arises in the context of the Standard Model, why B decays are relevant, and how BABAR gathers the necessary data. Specifically, we present the analysis of B 0 → rho0rho0 decays in a sample of 465 x 106 Upsilon(4S) → BB¯. We measure the corresponding branching fraction B = (0.92 +/- 0.32 (stat.) +/- 0.14 (syst.)) x 10 -6 and the longitudinal polarization fraction f L = 0.75+0.11-0.14 (stat.) +/- 0.04 (syst.). The evidence for the B 0 → rho0rho0 signal has a significance of 3.1 standard deviations (sigma), when the systematic uncertainties are included. There is insufficient evidence for B decays into similar modes and the corresponding upper limits are determined to be Br0f0 < 0.34 x 10-6, Bf0f0 < 0.16 x 10-6, Br0p+ p- < 8.7 x 10-6, Bp+p- p+p- < 21.1 x 10-6 at the 90% Confidence Level (CL).;We also investigate the proper-time dependence of the longitudinal component in the decay and measure the CP-violating coefficients SL = 0.3 +/- 0.7 (stat.) +/- 0.2 (syst.) and CL = 0.2 +/- 0.8 (stat.) +/- 0.3 (syst.). By combining these results with other measurements from the B → rhorho processes and performing an Isospin Analysis, we are able to restrict the unitarity angle alpha as well as its uncertainty due to penguin contributions, Deltaalpha. Namely, alpha = ( 92.4+6.0-6.5 )° with -1.8° < Deltaalpha < 6.7° at 1sigma CL. |
