Neutral B-meson mixing from unquenched lattice QCD with domain-wall light quarks and static b-quarks

Albertus, Conrado, Aoki, Yasumichi, Boyle, Peter A., Christ, Norman H., Dumitrescu, Thomas T., Flynn, Jonathan M., Ishikawa, Tomomi, Izubuchi, Taku, Loktik, Oleg, Sachrajda, Christopher T., Soni, Amarjit, Van de Water, Ruth S., Wennekers, Jan and Witzel, Oliver (2010) Neutral B-meson mixing from unquenched lattice QCD with domain-wall light quarks and static b-quarks. Preprint, 1-60.

Abstract

We demonstrate a method for calculating the neutral B-meson decay constants and mixing matrix elements in unquenched lattice QCD with domain-wall light quarks and static b-quarks. Our computation is performed on the "2+1" flavor gauge configurations generated by the RBC and UKQCD Collaborations with a lattice spacing of a approx 0.11 fm (a^-1 = 1.729 GeV) and a lattice spatial volume of approximately (1.8 fm)³. We simulate at three different light sea quark masses with pion masses down to approximately 430 MeV, and extrapolate to the physical quark masses using a phenomenologically-motivated fit function based on next-to-leading order heavy-light meson SU(2) chiral perturbation theory. For the b-quarks, we use an improved formulation of the Eichten-Hill action with static link-smearing to increase the signal-to-noise ratio. We also improve the heavy-light axial current used to compute the B-meson decay constant to O(α_s p a) using one-loop lattice perturbation theory. We present initial results for the SU(3)-breaking ratios f_Bs/f_Bd and ξ = f_Bs √B_Bs /f_Bd √B_Bd, thereby demonstrating the viability of the method. For the ratio of decay constants, we find f_Bs/f_Bd = 1.15(12) and for the ratio of mixing matrix elements, we find ξ = 1.13(12), where in both cases the errors reflect the combined statistical and systematic uncertainties, including an estimate of the size of neglected O(1/m_b) effects.

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Contributors

Author: Jonathan M. Flynn

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