Physicists at the LHCb experiment are measuring a tiny quantum phase called phi-s by tracking how beauty quarks decay into lighter particles inside the Large Hadron Collider. The Standard Model of particle physics accurately predicts most known particle behaviour, but it cannot explain dark matter, neutrino masses, or why matter dominates antimatter in the universe. The weak phase phi-s is predicted to be nearly zero by the Standard Model, so any deviation measured in these decays would signal the existence of new fundamental particles or forces—collectively called New Physics—operating at energy scales far beyond what any collider can directly produce. This project will analyse seven related decay modes of neutral B-mesons, using a novel technique that simultaneously extracts the unknown background contributions by exploiting flavour symmetries. Over the grant period, the available dataset will increase forty-fold, enabling the world’s first precision measurement of phi-s with this method, along with the most precise measurements of several related decay parameters. This is fundamental science with no immediate practical application. However, past discoveries in particle physics—such as the Higgs boson and the W and Z bosons—led directly to technologies like medical imaging (PET scanners) and the World Wide Web. A deeper understanding of the forces governing matter could, over decades, reshape how we generate energy, build materials, or probe the structure of space itself.
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The Standard Model (SM) of Particle Physics, whilst incredibly successfully, is known not to provide an adequate description for various observed physical phenomena. Precision measurements in the flavour sector are an ideal laboratory to search for New Physics (NP) beyond the SM at very high energy scales. This proposal will make precise measurements of highly NP sensitive decay rate ratios and weak phases, which arise in beauty-quark to strange- or down-quark transitions, using data collected at the Large Hadron Collider beauty (LHCb) experiment. The weak phase under consideration, called phi-s, has a very small and precisely known value in the SM making its determination a prime avenue for exploration of NP. However, interpretation of the experimental measurement, within the framework of the SM, is complicated by unknown polluting contributions. This issue is overcome in this proposal using a novel analysis technique, which simultaneously extracts the unknown contribution by exploiting flavour symmetries that are known to hold for the decays under study. This proposal will make the world's first precision measurement of phi-s using this analysis method. A family of seven inter-related decay modes of neutral B-mesons to hadrons, via vector-vector states, will be investigated. Beyond extraction of the weak phase, phi-s, understanding of the complex amplitude structure of these decays will provide insights into the role of New Physics in their decay dynamics. This proposal will make world's first and world's most precise measurements of various compelling decay rate parameters and phases which probe the fundamental nature of these processes. During the timeline of this proposal the available datasets will increase by a factor of forty and the project will deliver cutting-edge developments in analysis techniques and software tools. The outcome is a step-change in the physics reach, which will permit these precision measurements to be made for the first time.
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