Rare decays of heavy mesons to resonant channels

ended

Reliable and precise Standard Model predictions are becoming increasingly important in searches for new physics as the gap closes between experiment and theory. At CERN I will perform the first physical-quark-mass calculation of resonant form factors, including B → K*. This will allow future analyses of the LHCb data set to give significantly stronger probes of flavour non-universality and pave the way to discover new physics from the current 2.5σ tension in the R(K*) ratio of branching fractions observed at LHCb. Access to those form factors can be gained by studying rare decay processes like B→K* ℓ+ ℓ− . These processes, which involve neutral-current b→s quark transitions, are forbidden at tree level in the Standard Model. The resonant final state poses a particular challenge on the lattice due to its Euclidean formalism, which requires a careful study of the finite volume spectrum which can be related to pion-kaon asymptotic scattering states. The computational strategy is the distillation technique, which projects computationally expensive propagators into a subspace to be re-used efficiently. I have written high-performance-computing (HPC) code for distillation as part of the lattice QCD softwares Grid and Hadrons. This is free, open-source and runs in data production on various computing architectures, including GPU-based ones. The other main challenge of the computation of B → K* form factors is the treatment of the heavy-quark on the lattice. My work on B-meson mixing has demonstrated the viability of using a fully relativistic action for the heavy quark with fully controlled systematic errors. The combination of the careful treatment of the resonant effects and the innovative approach to incorporate the heavy quark will be essential to advance the precision physics goals in the B-sector, as well as provide the platform to study other related processes like Kγ → Kπ from QCD.