Research project is (co) funded by the Slovenian Research Agency.
UL Member: Faculty of Mathematics and Physics
Code: J1-70036
Project: $B\to\rho\ell\bar{\nu}$ form factors from lattice QCD
Period: 1. 3. 2026 - 28. 2. 2029
Range per year: 1,66 FTE, category: C
Head: Luka Leskovec
Research activity: Natural sciences and mathematics
Project description:
This project addresses one of the central open questions in particle physics: the precise determination of the Cabibbo–Kobayashi–Maskawa (CKM) matrix element |V_{ub}|. Current determinations from inclusive and exclusive B-meson decays are in tension, preventing a definitive test of the Standard Model.
We will compute the transition amplitudes for the semileptonic decay B → ρ(→ ππ)ℓν using first-principles numerical simulations of Quantum Chromodynamics (QCD) on the lattice. Unlike previous studies, we treat the ρ meson as an unstable resonance that decays into two pions and apply modern finite-volume formalisms to rigorously determine the infinite-volume physical amplitudes.
The calculation combines:
- lattice spectroscopy of ππ scattering,
- matrix element computations of B → ππℓν transitions,
- controlled extrapolations to the physical pion mass, continuum limit, and infinite volume.
The final result will provide Standard Model predictions for B → ρℓν form factors with a complete error budget. This new exclusive channel will enable an independent determination of |V_{ub}| and may help resolve the long-standing discrepancy between inclusive and exclusive determinations. In addition, we will compute the analogous D → ρℓν transition, providing a cross-check in the charm sector where CKM parameters are well known. The project employs state-of-the-art lattice QCD methods and high-performance computing resources (VEGA, Leonardo, ATOS) and contributes directly to international efforts in flavor physics.
