Measurements of Branching Fraction and CP Violation InB Meson Rare Decays to Final States Containing Eta Or Eta' Mesons in the BaBar Experiment at SLAC. PDF Download

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Languages : en
Pages : 383

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Book Description
Note that the main goal of this thesis work is the measurement of the branching fractions, charge asymmetry, and Time-Dependent CP Violation in [eta]'K° mode. All other measurements are reported here for completion because they are connected by similar physics arguments. They are part of the Milan analysis activity, done by undergraduate students. They should not be considered as done in this thesis work. The measurements of the two body-modes [eta][eta], [eta][phi], and [eta]'[phi] are used to determine a theoretical bound based on SU(3) flavor symmetry for the difference between SM prediction and the experimental measurements of CP violation parameters in b → s loop-dominated modes. In general for this estimation we need to measure the branching fractions (or upper limits) of neutral B decays to two-body modes with [eta]', [eta], [phi], [omega], [pi]°, K°, K*° [13, 14, 15, 16]. There is an important issue related to the branching fractions of [eta]'K (charged and neutral) modes. Since the discover of B → [eta]'K in 1997 [17] with high branching fraction (higher than expected), it was found that the corresponding mode with [eta] is suppressed. This fact was pointed out by Lipkin in 1991 [18]. In particular, using arguments concerning the [eta]-[eta]' mixing angle and the parity of K or K* we can say that [eta]'K and [eta]K* are enhanced, while [eta]K and [eta]'K* are suppressed. This scheme is experimentally verified. The branching fraction of all these modes are already measured, but the B° → [eta]K°. So it is important to measure also this mode to complete the scenario. Finally we report on the measurements of the radiative modes B → [eta]'K[gamma] and of the three-body mode B → [eta]'[eta]'K. Both cases are good candidates to manifest effects due to NP in CP violations [19, 20]. For all measurements we use an unbinned maximum likelihood fit to extract the number of signal yields and CP parameters. To perform these fits we have developed a flexible program in C++ language, called MiFit, which has taken a consistent part of the work described in this thesis. This program is used in all Milan analyses. All these measurements have been presented in conferences and published in Physical Review Letters or Physics Review D (Rapid Communication). These measurements are official BABAR results, approved by the Collaboration. The thesis is structured in eight chapters. In the first chapter we describe the CP violation and how it is explained in the SM. We give the theoretical description of the modes studied in this thesis. We report also the latest main results for the CP violation. In the second chapter we describe the BABAR detector with a description of each sub-detector. In the third chapter we describe the software used by the collaboration, in particular the code used in the events reconstruction, which is described in the fourth chapter. In the fifth chapter we describe the software used to selected the events and the MiFit program. After that, in the sixth chapter we show the discriminating variables used for the events selection and how the selection is done. In the last two chapters we report the analyses and results of the branching fractions and charge asymmetries measurements and the time-dependent CP asymmetries analysis of the mode B° → [eta]'K°, respectively.