Doc. dr. Luka Leskovec and his collaborators recently broke new ground in lattice QCD. In their latest Editor’s Suggestions of Physical Review Letters, they present the first ab initio calculation of the semileptonic decay B → ρ ℓ ν, fully accounting for the ρ meson’s nature as a resonance. Using the Lellouch-Lüscher finite-volume formalism, the researchers extracted the B → ππ ℓ ν transition amplitudes. They analytically continued them to the ρ pole to obtain the complete set of resonance form factors. These results, visualized in the accompanying plot, provide a critical path towards resolving the long-standing discrepancy in determinations of the smallest and least known CKM matrix element – |V_{ub}| and open the door to precision tests of the Standard Model via multi-hadron final states.