Speaker
Description
We compare multi-hadron and single-hadron treatments of $B\to\rho\ell\bar{\nu}$ in lattice QCD using one $N_f=2+1$ clover-Wilson ensemble with $m_\pi \approx 320$ MeV, where the $\rho$ has a decay width of approximately $40$ MeV. In the multi-hadron analysis, the unstable $\rho$ is treated as an interacting $I=1$, $P$-wave $\pi\pi$ final state with the full use of the finite-volume formalism. In contrast, the stable-$\rho$ analysis assumes that the state produced with a $\bar{q}\gamma_\mu q$ interpolator at an intermediate Euclidean-time-distance is the correct state and determines the form factors from its matrix elements. The single-hadron treatment reproduces the qualitative $q^2$ dependence but slightly shifts some form factors (statistically significantly).