B -> D* l nu at zero recoil: an update

Abstract

We present an update of our calculation of the form factor for B -> D* l nu at zero recoil, with higher statistics and finer lattices. As before, we use the Fermilab action for b and c quarks, the asqtad staggered action for light valence quarks, and the MILC ensembles for gluons and light quarks (L\"uscher-Weisz married to 2+1 rooted staggered sea quarks). In this update, we have reduced the total uncertainty on F(1) from 2.6% to 1.7%. At Lattice2010 we presented a still-blinded result, but this writeup includes the unblinded result from the September 2010 CKM workshop.