CP-PACS Collaboration, :, A. Ali Khan, S. Aoki, R. Burkhalter, S. Ejiri, M. Fukugita, S. Hashimoto +11
Abstract
We present a calculation of the B and D meson decay constants in lattice QCD with two (Nf=2) flavours of light dynamical quarks, using an O(a)-improved Wilson action for both light and heavy quarks and a renormalization-group improved gauge action. Simulations are made at three values of lattice spacing a=0.22, 0.16, 0.11 fm and four values of sea quark mass in the range m_PS/m_V \ = 0.8-0.6. Our estimate for the continuum values of the decay constants are fBd = 208(10)(11) MeV, fBs = 250(10)(13)(⁺⁸₋₀) MeV, fDd = 225(14)(14) MeV, fDs = 267(13)(17)(⁺¹⁰₋₀) MeV for Nf=2 where the statistical and systematic errors are separately listed, and the third error for fBs and fDs show uncertainty of determination of strange quark mass. We also carry out a set of quenched simulations using the same action to make a direct examination of sea quark effects. Taking the ratio of results for Nf=2 and Nf=0, we obtain fb^Nf=2/fb^Nf=0 = 1.11(6), fbs^Nf=2/fbs^Nf=0 = 1.14(5), fd^Nf=2/^Nf=0 = 1.03(6), fds^Nf=2/^Nf=0 = 1.07(5). They show a 10-15% increase in the Nf=2 results over those of Nf=0 for the B meson decay constants, while evidence for such a trend is statistically less clear for the D meson decay constants.