Heavy-Light Mesons with Quenched Lattice NRQCD: Results on Decay Constants

We present a quenched lattice calculation of heavy-light meson decay constants, using non-relativistic (NRQCD) heavy quarks in the mass region of the b quark and heavier, and clover-improved light quarks. The NRQCD Hamiltonian and the heavy-light current include the corrections at first order in the expansion in the inverse heavy quark mass. We study the dependence of the decay constants on the heavy meson mass M , for light quarks with the tree level (cSW = 1), as well as the tadpole improved clover coefficient. We compare decay constants from NRQCD with results from clover (cSW = 1) heavy quarks. Having calculated the current renormalisation constant ZA in oneloop perturbation theory, we demonstrate how the heavy mass dependence of the pseudoscalar decay constants changes after renormalisation. For the first time, we quote a result for fB from NRQCD including the full one-loop matching factors at O(α/M). PACS numbers: 12.38.Gc, 12.39.Hg (HQET) 13.20.He (leptonic and semileptonic decays of bottom mesons), 14.40.Nd