Advancing Non-Perturbative Heavy Quark Physics

• Applicant: Dr. Simon Kuberski
• Subject Area: Nuclear and Elementary Particle Physics, Quantum Mechanics, Relativity, Fields
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 559290516

The Standard Model (SM) of particle physics has been highly successful in describing fundamental particles and their interactions. However, it leaves several phenomena unexplained, including dark matter, the matter-antimatter asymmetry, and the origin of neutrino masses. These open questions motivate the search for physics beyond the SM. Several deviations from SM predictions have emerged in the bottom quark sector, raising hopes for identifying new physics through precision comparisons between experimental results and theoretical predictions. These include long-standing tensions between inclusive and exclusive determinations of CKM matrix elements and tests of lepton flavor universality in bottom hadron decays. A key objective of this project is to provide precise lattice QCD input to clarify these tensions. Lattice QCD offers a powerful non-perturbative framework for computing hadronic observables from first principles and plays a crucial role in heavy quark physics. However, simulating bottom quarks poses challenges due to their higher mass. Specifically, cutoff effects, deviations from the continuum theory, become significant because the bottom quark mass is large compared to the inverse lattice spacing on most large-volume QCD gauge ensembles. Current methods often rely on extrapolations to the bottom scale, which can introduce large uncertainties from cutoff effects and the quark mass extrapolation. This project aims to address these challenges using the step-scaling approach, which replaces the traditional quark mass extrapolation with an interpolation between relativistic heavy quarks and the static limit of Heavy Quark Effective Theory. This method reduces significantly systematic uncertainties from the extrapolations to the B-meson scale and the continuum limit. By combining large-volume simulations with a dedicated set of small-volume simulations, where bottom quarks can be treated more precisely on finer lattice spacings, this approach offers control at the B-scale. In addition to the step-scaling method, the project will develop advanced noise-reduction techniques to achieve more precise extractions of ground-state matrix elements, further improving the reliability of key observables. By achieving unprecedented precision in bottom quark observables and reducing key systematic uncertainties, this project will provide essential theoretical input for interpreting experimental results at LHCb, Belle II, and other experiments. The improved precision will deepen our understanding of heavy quark physics and may help uncover signals of physics beyond the Standard Model.

• DFG Programme: Emmy Noether Independent Junior Research Groups