[en] The authors present a study of the inclusive D*^± production in the decay of Υ(1S) using (98.6 ± 0.9) x 10⁶ Υ(2S) mesons collected with the BABAR detector at the Υ(2S) resonance. Using the decay chain Υ(2S) → π⁺π^-Υ(1S), Υ(1S) → D*^±X, where X is unobserved, they measure the branching fraction Β(Υ(1S) → D*^±X) = (2.52 ± 0.13(stat) ± 0.15(syst))% and the D*^± momentum distribution in the rest frame of the Υ(1S). They find evidence for an excess of D*^± production over the expected rate from the virtual photon annihilation process Υ(1S) → γ* → c(bar c) → D*^± X.

[en] This work is the result of the researchers carried out during a three years Ph.D. period in the BABAR experiment. The first chapter consists in an introduction to the theoretical aspects of the D⁰ meson lifetime determination and CP violation parameters, as well as an overview of the CP violation in the B sector, which is the main topic of the experiment. The description of the experimental apparatus follows with particular attention to the Silicon Vertex Tracker detector, the most critical detector for the determination of decay vertices and thus of lifetimes and time dependent CP violation asymmetries. In the fourth chapter the operation and running of the vertex detector is described, as a result from the experience as Operation Manager of the SVT, with particular attention to the safety of the device and the data quality assurance. The last chapter is dedicated to the determination of the D⁰ meson lifetime with the BABAR detector, which is the main data analysis carried out by the candidate. The analysis is characterized by the selection of an extremely pure sample of D⁰ mesons for which the decay flight length and proper time is reconstructed. The description of the unbinned maximum likelihood fit follows, as well as the discussion of the possible sources of systematic uncertainties. In the appendix is also presented a preliminary study of a possible development regarding the determination of mixing and CP violation parameters for the D⁰ meson.

[en] Since 2005 and 2006, respectively, Geant4 versions 7.1 and 8.3 have been available, providing: improvements in modeling of multiple scattering; corrections to muon ionization and improved MIP signature; widening of the core of electromagnetic shower shape profiles; newer implementation of elastic scattering for hadronic processes; detailed implementation of Bertini cascade model for kaons and lambdas, and updated hadronic cross-sections from calorimeter beam tests. The effects of these changes in simulation are studied in terms of closer agreement of simulation using Geant4 versions 7.1 and 8.3 as compared to Geant4 version 6.1 with respect to data distributions of: the hit residuals of tracks in BABAR silicon vertex tracker; the photon and K_L⁰ shower shapes in the electromagnetic calorimeter; the ratio of energy deposited in the electromagnetic calorimeter and the flux return of the magnet instrumented with a muon detection system composed of resistive plate chambers and limited-streamer tubes; and the muon identification efficiency in the muon detector system of the BABAR detector.