"This thesis is divided in different sections. After a short introduction about the thesis contents, the theory chapter presents the Standard Model of Particle Physics (SM), with an emphasis on those properties of flavour physics, such as oscillations. In this chapter a brief comment on radiative decays, the main topic through the thesis, is given, to present the specific theoretical description of these processes. The European Centre of Nuclear Research (CERN) is introduced in the second chapter, where the nature of such organization and the different experiments it holds are explained. Special emphasis is given for the LHCb experiment, which is the one that collected the data used in the analysis. The third chapter describes the monitorization and re-calibration of the SPD sub- detector, which is the one in charge of the discrimination between photons and other electromagnetic particles. During the Run 1 (2011-2012), this sub-detector suffered from ageing due to the presence of radiation inside the LHCb cavern. This ageing led to a drop in the SPD cell efficiencies, which could imply a loss in the data quality. The SPD is key in the context of radiative decays due to the presence of photons in the radiative final states and due to the fact that the main sources of background for radiative decays are related to the mis-identification of other particles as photons. With the work presented in this thesis, the performance of the SPD sub-detector reached the same status than it did for the beginning of Run 1, which corresponds to an almost flat cell efficiency around 95%. This recovery in efficiencies was performed by applying a correction factor calculated through the study of cosmic ray data and collision data from 2015. The fourth chapter describes a software tool developed within the radiative decays context. This tool is aimed for a better description of the photon/neutral pion separation variable, which is built making use of the electromagnetic clusters that these particles leave in the LHCb electromagnetic calorimeter (ECAL). This tool builds a variable that separates between the two particles but discrepancies between the data and the simulation distributions are observed. Because of this, two additional tools were developed to improve the agreement between them. These tools trust that the separation variable can be binned in terms of the particle transverse momentum and pseudorapidity. The first of the tools, "efficiency table tool", assigns the efficiency for a certain 2-dimensional bin as a weight to the simulation sample, so the distribution is corrected and matches the one for data. The "resampling tool", however, creates a new variable from calibration histograms built from background- subtracted distributions, trusting all radiative decays to have a similar behaviour in the 2-dimensional bins. The two tools can also be applied to neutral pions selection. The main chapter of the thesis is related to the measurement of the ratio of branching fractions for Bs decaying into phi (which decays into two kaons) and a photon and Lambda_b, decay into a Lambda bayron (which decays into a kaon and a proton) and a photon with respect to the best controlled radiative decay, Bd decaying into a K* (which decays into a kaon and a pion) and a photon, as well as the measurement of the direct CP asymmetry for the Lambda_b and Bd decays. This analysis also implies the first observation of a b-baryon radiative decay and constitutes the best measurement of the observables presented above. The analysis is performed over the whole Run 1 LHCb dataset (3 inverse fb). Special care is applied to the Lambda_b decay since it had never been done before; taking into account the different resonances that may intervene (that cannot be distinguished since they overlap and interfere). A 2- dimensional binning (on the resonance mass and on the proton angle) is defined for the study of the efficiencies, as recommended by the theory approaches to this decay and trusting (and confirmed afterwards) the different resonance decays to give a similar efficiency for the offline selection for a given bin. The thesis concludes with an overview of the whole work presented, given the calculated results for the physical observables and comparing them to the previously measured ones in the LHCb"--TDX.

This book discusses the study of double charm B decays and the first observation of B0->D0D0Kst0 decay using Run I data from the LHCb experiment. It also describes in detail the upgrade for the Run III of the LHCb tracking system and the trigger and tracking strategy for the LHCb upgrade, as well as the development and performance studies of a novel standalone tracking algorithm for the scintillating fibre tracker that will be used for the LHCb upgrade. This algorithm alone allows the LHCb upgrade physics program to achieve incredibly high sensitivity to decays containing long-lived particles as final states as well as to boost the physics capabilities for the reconstruction of low momentum particles.

LHCb is an experiment which is designed to perform flavour physics measurements at the LHC. Charged two-body charmless B decays (e.g. B^0 -> Kpi, pipi, B_s->KK, etc) receive significant contributions from loop diagrams and are thus sensitive probes of New Physics. Study of these modes is therefore an important physics goal of LHCb. First results will be presented, using around 37 pb^{-1} of data collected at \sqrt{s}=7 TeV in 2010. These results illustrate the power of the LHCb trigger system and particle identification capabilities of the RICH detectors in isolating clean samples of each final state, and include preliminary measurements of direct CP-violation in certain key modes. The prospects for these measurements in the coming run will be presented. A brief survey will also be given of results and prospect in other areas of the LHCb physics programme.

The Standard Model (SM) of particle physics has withstood thus far every attempt by experimentalists to show that it does not describe data. We discuss the SM in some detail, focusing on the mechanism of fermion mixing, which represents one of its most intriguing aspects. We discuss how this mechanism can be tested in b-quark decays, and how b decays can be used to extract information on physics beyond the SM. We review experimental techniques in b physics, focusing on recent results and highlighting future prospects. Particular attention is devoted to recent results from b decays into a hadron, a lepton and an anti-lepton, that show discrepancies with the SM predictions — the so-called B-physics anomalies — whose statistical significance has been increasing steadily. We discuss these experiments in a detailed manner, and also provide theoretical interpretation of these results in terms of physics beyond the SM.