B2DTauNu · Model-independent angular analysis of semileptonic B meson decays involving tau leptons

Model-independent angular analysis of semileptonic B meson decays involving tau leptons

The overarching goal of particle physics research is to understand the nature of fundamental particles and their interactions. All of the visible matter in our universe, ranging from tiny bacteria all the way up to stars and galaxies, is formed from the finite set of atoms appearing in the periodic table. Atoms themselves are composed from an even smaller set of fundamental particles, namely the electron, the up quark, and the down quark, all of which are held together by force-carrying particles such as photons and gluons. In the earliest moments of our universe immediately after the Big Bang, quarks and leptons from two heavier families were also present in abundance, as were their antimatter partners. Why our universe consists of thee particle generations, and what happened to all of the antimatter present in our early universe, remain central questions in particle physics today. The field of flavour physics, within which this project falls, tries to address these questions and more by studying the properties of quarks and leptons in all three families. By studying the interactions of different quarks and leptons, flavour physicists hope to achieve a complete understanding of the Standard Model (SM), our most successful theory to date for explaining the universe at tiny distance scales. In attempting to pin down the SM, chinks in its considerable armoury could also appear. Indeed, hints of deviations from the SM, which may indicate the presence of new particles and forces, have previously been observed in past experiments and at the CERN LHCb experiment. This project aims to extend our understanding of these deviations, which are collectively known as “flavour anomalies”, via an angular analysis of beauty quarks decaying to a charm quark plus a tau lepton and a neutrino in LHCb data. The b -> c tau nu process is understudied historically, given the relatively small numbers of beauty quarks produced in previous experiments and the difficultly with which tau leptons can be identified in experimental data. At the LHCb experiment, however, trillions of beauty quarks have thus far been produced during Run 1 and 2, and great advances have been made in the reconstruction and identification of beauty hadron decays to tau final states. Leveraging these developments, this project makes use of the full LHCb Run 1 + 2 dataset to study B0 -> D* tau nu decays, in order to measure a set of 13 physical observables which further describe the nature of the b -> c tau nu quark transition. These observables will help theoretical physicists interrogate the SM with additional rigour, in order to determine whether the flavour anomalies are genuine hallmarks of New Physics or simply a result of statistical fluctuations or systematic experimental issues. For society as a whole, the project thus contributes considerably to our fundamental knowledge of the universe and the behaviour of its smallest constituents.

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