Study of radiative decays at LHCb and search for the Λb0->pπ-γ decay

Abstract

[eng] The main goal of this thesis is to study the radiative decays produced in one of the four big detectors of LHC, LHCb, which focuses on the study of matter-antimatter asymmetry through b and c quarks. In particular, the Λb0->pπ-γ process is studied from the data collected during the Run 1 of LHC in 2011 and 2012. In order to reduce the systematic uncertainties, a similar process, Λb0->pK-γ is used as a normalisation mode. This mode shares the same kinematics as our signal, with the difference that is less suppressed by the Cabibbo-Kobayashi-Maskawa matrix as it involves an b->sγ flavour changing neutral current instead of a b->dγ. In parallel, an inclusive radiative trigger selection has been developed to be used starting in the Run 3 of LHC in 2022. This inclusive selection will allow to save a wide variety of radiative decays while adapting to the new data writing scheme, where only the signal candidate will be saved, in opposition to the Run 1 and 2 setups where the whole event is saved. These radiative processes are of great interest as they are sensitive to interactions or particles beyond the Standard Model of Particle Physics, and so they serve as strong tests. Up to this date, the results from particle physics experiments have confirmed the Standard Model predictions, despite there are some phenomena which have not been able to be included in it yet. These phenomena include the matter-antimatter asymmetry observed in the universe, dark matter or dark energy. From the theorical point of view, for example, the Standard Model does not include a quantum field theory description of general relativity, while it does for the strong and electroweak interactions. It is for this reason that the measurement of radiative decays is also useful in determining the validity of the different theoretical models developed to explain part of these phenomena.

[spa] Esta tesis tiene como objetivo el estudio de las desintegraciones radiativas recogidas por el detector LHCb, en concreto del proceso Λb0->pK-γ, empleando los datos recogidos durante el Run 1 del acelerador LHC, correspondientes a 2011 y 2012. A su vez, también se ha desarrollado la selección de trigger inclusiva que comenzará a emplearse en el Run 3, a partir de 2022. Este tipo de procesos es especialmente sensible a efectos producidos por interacciones o partículas no contempladas en el Modelo Estándar (ME) de la física de partículas, por lo que sirven como comprobación de este. Hasta la fecha, los resultados experimentales de la física de partículas han corroborado las predicciones del ME, a pesar de que existen ciertos fenómenos que todavía no es capaz de incorporar, como la asimetría entre materia y antimateria observada en el universo o la materia y energía oscuras. En el plano teórico, el ME no incluye una descripción de la relatividad general como teoría cuántica de campos, mientras sí lo hace para la interacción electromagnética, nuclear fuerte y débil. Es por ello que la medida de este tipo de desintegraciones también sirve como prueba de la validez de los diferentes modelos teóricos desarrollados para explicar varios de estos fenómenos.