Beauty to Open Charm Measurements at LHCb and Other Flavourful Friends

Abstract

The Standard Model (SM) of particle physics, which seeks to provide a fundamental description of the universe’s smallest constituents, is an incredibly successful theory by many metrics. There is, however, good reason to expect that it does not provide the full picture. The exact nature of such a new theory remains uncertain, and there is currently limited experimental evidence of significant deviations from the SM. Observation of such deviations is an essential prerequisite for the emergence of a new fundamental theory that provides a more consistent description of all empirical observations. This, in turn, requires high-precision measurements. LHCb is an experiment designed explicitly with the precision paradigm in mind, particularly for beauty and charm physics, and has recently undergone extensive upgrades. For measurements taken by this new detector to be relied upon, its early data must first be validated, and this thesis details efforts towards this goal, particularly through production cross-sections of beauty hadrons. Such early measurements utilise “beauty to open charm” channels, which have recently shown hints of a theory-experiment discrepancy, and both experimental and theoretical analyses seeking to clarify this situation are also explained here. Firstly, I outline an LHCb analysis probing for the influence of New Physics in ¯B0s → D+s π− through measurements of its CP asymmetry, an observable expected to be sensitive to such effects. A symmetry-based analysis of the theoretical side of this puzzle comes later, where it is concluded that excess symmetry breaking cannot be attributed as the source of the observed tensions. This was limited somewhat by a lack of experimental data, but the data situation is more bountiful for B → DD′, which also benefits from access to direct CP violation. A more in-depth analysis using a similar method was therefore also applied to this family of decays, and the details of this can also be found here. The predictions from this analysis were found to be consistent with the experimental data; however, they had improved precision, and predictions were possible for observables yet to be determined experimentally. Evidence for breaking of the traditional assumption of isospin symmetry in production was also shown at a significance of 2.5σ.

Date of Award	31 Dec 2024
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Conor Fitzpatrick (Supervisor)