Dlν from Lattice QCD

where w = v · v and G(1) = 1. At zero recoil (w = 1) heavy-quark symmetry requires FB→D∗(1) to be close to 1. So, |Vcb| is determined by dividing measurements of dΓ/dw by the phase space and well-known factors, and extrapolating to w → 1. This yields |Vcb|FB→D∗(1), and FB→D∗(1) is taken from “theory.” To date models [ 1] or a combination of a rigorous inequality plus judgment [ 2] have been used to estimate FB→D∗(1) − 1. In this work [ 3] we calculate FB→D∗(1) with lattice gauge theory, in the so-called quenched approximation, but the uncertainty from quenching is included in the error budget. The “form factor” FB→D∗(w) is a linear combination of several form factors of the matrix elements 〈D∗|Vμ|B〉 and 〈D∗|Aμ|B〉. At zero recoil all form factors but hA1 are suppressed by phase space, so FB→D∗(1) = hA1(1) = 〈D (v)|A|B(v)〉, (2)