$B \to \rho \ell \bar{\nu}$ resonance form factors from $B \to \pi \pi \ell \bar{\nu}$ in lattice QCDLeskovec, Luka (Avtor) Meinel, Stefan (Avtor) Petschlies, Marcus (Avtor) Negele, John W. (Avtor) Paul, Srijit (Avtor) Pochinsky, Andrew (Avtor) physics of elementary particlesparticle interactionslattice QCDform factorsThe decay $B \to \rho \ell \bar{\nu}$ is an attractive process for determining the magnitude of the smallest Cabibbo-Kobayashi-Maskawa matrix element, $|V_{ub}|$, and can provide new insights into the origin of the longstanding exclusive-inclusive discrepancy in determinations of this standard-model parameter. This requires a nonperturbative QCD calculation of the $B \to \rho$ form factors $V$, $A_0$, $A_1$, and $A_{12}$. The unstable nature of the $\rho$ resonance has prevented precise lattice QCD calculations of these form factors to date. Here, we present the first lattice QCD calculation of the $B \to \rho$ form factors in which the $\rho$ is treated properly as a resonance in $P$-wave $\pi \pi$ scattering. To this end, we use the Lellouch-Lüscher finite-volume formalism to compute the $B \to \pi \pi$ form factors as a function of both momentum transfer and $\pi \pi$ invariant mass, and then analytically continue to the $\rho$ resonance pole. This calculation is performed with 2 + 1 dynamical quark flavors at a pion mass of approximately 320 MeV, and demonstrates a clear path toward results at the physical point.20252025-04-24 11:37:47Članek v reviji168786UDK: 539.120.811ISSN pri članku: 0031-9007DOI: 10.1103/PhysRevLett.134.161901COBISS_ID: 234136323sl