B meson proper time measurements with the LHCb experiment: impact on physics parameters and calibration methods

The LHCb (Large Hadron Collider beauty) experiment is one of the four experiments at the LHC, and is specifically dedicated to explore the B-meson dynamics. To this end, LHCb will exploit the large beauty production cross section, expected to be about 500 µb at 14 TeV p-p collisions. Differently from the B-factory case, the hadronization of the b-quarks at LHC will generate all the possible B-hadrons, remarkably the Bs and Bc mesons, where the present experimental knowledge is still rather poor. The number of b/b_bar pairs produced at the LHCb interaction point will be of the order of 10^12 per year, allowing for the search of extremely rare decays, with branching fractions at the level of 10^-9. In order to reduce the acquisition rate to a sustainable level (order of 2 kHz), maintaining at the same time a high efficiency on the signals of interest, LHCb is provided with an efficient and flexible trigger system. LHCb, by means of its vertex detector, will be able to reconstruct the proper time of decays with a great accuracy (~ 40 fs) and therefore it is well suitable to study minutely CP violation for the very fast oscillating Bs mesons. Moreover the features of the LHCb detector are also suitable to study the charm and tau decays, which also other another great opportunity to find out New Physics. For my Ph.D thesis, I developed a new procedure (called the FITPull method) to monitor and check the measurement of the B decay proper time and its error. The procedure is based on the use of the kinematical constraints between the track parameters of the particles involved in the B decays, without relying on Monte Carlo information. The method can be calibrated on the decay mode J/psi->>µµ, which will be exploited by LHCb as a general monitor channel for the charged tracks calibration, with the aim of identifying and eventually recovering imperfect measurements of the track parameters. I applied the FITPull method to two different reference channels: B --> h+h- and Bs -> Ds pi, evaluating its performance in correcting track measurement errors. I have also contributed to the implementation of a software tool, the GlobalFitter , that is used to compute the FITPull distributions of the input track parameters. The thesis is organized in 4 chapters. In Chapter 1 the LHCb experiment, its sub-detectors and trigger system are described. Chapter 2 introduces the theoretical framework of the B-meson mixing and CP violation in the Standard Model, with some details of the relevant measurements that LHCb will perform. In Chapter 3 the FITPull method is described, and finally Chapter 4 gathers the results of some studies on Monte Carlo simulated data, by investigating the impact of the calibration method on the physical quantities which are mostly affected by the precision of the B proper time measurement.