B radiative decays at LHCb: measurement of B→ K∗γ isospin asymmetry and preparation of Run 3 analyses
[eng] The Standard Model (ME) of particle physics is the theory that describes fundamental particles and their interactions, except gravity. Despite its success and accuracy in predicting phenomena, it is known that it is not a complete theory. It does not describe dark matter or energy, the asymmet...
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| Tipo de recurso: | tesis doctoral |
| Estado: | Versión publicada |
| Fecha de publicación: | 2025 |
| País: | España |
| Institución: | Universidad de Barcelona |
| Repositorio: | Dipòsit Digital de la UB |
| OAI Identifier: | oai:diposit.ub.edu:2445/226472 |
| Acceso en línea: | https://hdl.handle.net/2445/226472 http://hdl.handle.net/10803/696483 |
| Access Level: | acceso abierto |
| Palabra clave: | Física de partícules Acceleradors de partícules Gran Col·lisionador d'Hadrons Partícules (Matèria) Particle physics Particle accelerators Large Hadron Collider (France and Switzerland) Particles |
| Sumario: | [eng] The Standard Model (ME) of particle physics is the theory that describes fundamental particles and their interactions, except gravity. Despite its success and accuracy in predicting phenomena, it is known that it is not a complete theory. It does not describe dark matter or energy, the asymmetry between matter and antimatter in the Universe, or the origin of neutrino mass. Consequently, it is vitally important to investigate possible extensions of this model and measure processes that may reveal new physics. An experiment that contributes to this task is the LHCb, one of the four main detectors located in the LHC particle accelerator operated by CERN. His study focuses on high-precision measurements of particles involving heavy quarks b and c. Rare radiative decays of B mesons are an ideal platform to test EM and study its possible extensions. These decays cannot occur through tree diagrams within the description of the ME, but take place through loops in which unknown particles could participate, thus altering the observable quantities. This thesis presents three interconnected topics within the study of rare radiative decays of B mesons: the experiment's calorimeter monitoring tools, the radiative inclusive selections in the trigger system, and the measurement of the isospium asymmetry of the B→K*γ decay. The measurement of the isospium asymmetry of the B→K*γ decay has been done using data from Run 2, which covers the years 2015 to 2018. The other two tasks have been carried out within the framework of Run 3, starting in 2021. Between these two Runs, an ambitious improvement program, called Upgrade I, has made it possible to increase the capacity of the detector. Some of the subdetectors have been completely renewed, the data reading system has been improved to facilitate 40 MHz reading and the hardware phase of the trigger has been dismantled, becoming the first large detector with a completely software-based trigger. This set of improvements has made it possible to increase the instantaneous luminosity at which the detector operates by a factor of five, thus gaining sensitivity and its precision measurements. The monitoring of the calorimeter makes it possible to detect anomalies in the data collection and provides information on the origin of the problem in order to be able to solve it quickly. It has been a critical function during the commissioning period of Run 3, until the system has reached its stable operation. Trigger selections inclusive of radiative processes make it possible to capture events of this type and rule out those that constitute background noise, thus keeping the volume of data stored within the limits of the system. The selections for the new instantaneous high luminosity environment have been optimized and the BDT multivariable method has been used in order to obtain the best possible signal efficiency. Finally, the measurement of the isospy asymmetry of the B→K*γ decay is obtained for the first time with data from the LHCb and with an accuracy comparable to the measurements of other experiments, validating the ME and applying constraints on its possible extensions, in particular extensions of supersymmetry and extra Higgs sectors. |
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