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Angular analysis of the decay B+->(K*+->K+π0)µ+µ− with the LHCb experiment

Kopečná, Renata

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In this thesis, major steps towards the first angular analysis of the rare B+->(K*+->K+π0)µ+µ− decay are presented. This study is of great interest in the context of validating the anomalies observed in recent years in the properties of b quark decays to an s quark and two muons. If confirmed, these observations could represent a sign of physics beyond the Standard Model. The analysis is based on the world-largest sample of B meson decays which was collected using the LHCb experiment at the Large Hadron Collider during the years 2011 - 2018, corresponding to an integrated luminosity of 9.0 fb^−1 of pp collision data. Although less than one in a million B+ mesons decays to K∗+µ+µ−, a total of 271±28 candidates is selected. The main challenge of the decay mode is the presence of a neutral π0 meson in the final state. This thesis represents the first proof of feasibility of an angular analysis involving a neutral particle in the final state using the LHCb dataset. The event selection is optimized in order to remove various sources of background pollution while maximizing the available angular acceptance. A detailed simulation of the detector is used to unfold the effects of the detector acceptance, reconstruction and selection on the angular distributions. The maximum likelihood fit to extract the angular parameters of the decay B+->(K*+->K+π0)µ+µ− has been developed and tested using thousands of pseudoexperiments. It is shown that the complicated background structure together with the low statistical power of the available data sample result in large uncertainties. However, the analysis proves to be sensitive enough to disentangle an anomaly coherent with that observed in other decays with more than two standard deviations of significance.

Document type: Dissertation
Supervisor: Hansmann-Menzemer, Prof. Dr. Stephanie
Place of Publication: Heidelberg
Date of thesis defense: 15 December 2021
Date Deposited: 22 Dec 2021 08:12
Date: 2021
Faculties / Institutes: The Faculty of Physics and Astronomy > Institute of Physics
DDC-classification: 530 Physics
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