Lattice calculation of the Isgur-Wise functions τ1/2 and τ3/2 with dynamical quarks

We perform a dynamical lattice computation of the Isgur-Wise functions τ1/2 and τ3/2 at zero recoil. We consider three different light quark masses corresponding to 300 MeV ∼< mPS ∼< 450 MeV, which allow us to extrapolate our results to the physical u/d quark mass. We find τ1/2(1) = 0.296(26) and τ3/2(1) = 0.526(23). Uraltsev's sum rule is saturated up to 80% by the ground state. We discuss implications regarding semileptonic decays B → Xc l ν and the associated ''1/2 versus 3/2'' puzzle.