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Title: Weak decays of beautiful pseudoscalar mesons with Lattice Quantum Chromodynamics
Author: Cooper, Laurence
ISNI:       0000 0004 9359 648X
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2020
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Weak decays of beautiful mesons can be used to probe the validity of our best model of particle physics: the Standard Model. In this thesis, I use specialised techniques to overcome practical challenges associated with the large mass of valence b quarks to study a selection of decays of B mesons with Lattice Quantum Chromodynamics. After introducing these modern methods, I report on my progress on calculating the vector current form factors for B_c to D_s. This decay is allowed at the one-loop level and so my vector current form factors will be used, along with future analysis of the tensor form factor, to describe the short-distance physics of this transition. I then present a comprehensive calculation of the B_c to B_s(d) vector current form factors based on a non-relativistic field theory approach for the bottom quark. I conclude by comparing my results with another calculation that uses an alternative approach for the heavy valence quark, an important test of our best lattice techniques. Combining data from this study with my calculation, I give the first prediction of the decay rates Γ (B_c⁺ to B_s⁰ ̅ℓ νℓ) and Γ (B_c⁺ to B⁰ ̅ℓ νℓ) from lattice QCD. Next, exploratory work on the long-distance contributions of charmonia on the flavour-changing neutral current process B to K is discussed. Difficulties with intermediate states that lead to divergences in the corresponding correlation function are addressed by again using the non-relativistic approach for the b quark. Finally, I digress from weak decays to explore applications of the Sherman-Morrison-Woodbury formula within the framework of lattice QCD. I find computational efficiencies in determining the inverse and the determinant of quark matrices. Potential applications are discussed.
Supervisor: Wingate, Matthew Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
Keywords: weak decays ; B physics ; hadrons ; lattice gauge theory ; particle physics ; Quantum Field Theory ; lattice QCD ; quantum chromodynamics ; lattice field theory ; mesons