$B^0_s - \bar{B^0_s}$ Mixing Parameters from Unquenched Lattice QCD

Dalgic, Emel; Gray, Alan; Gamiz, Elvira; Davies, Christine T. H.; Lepage, G. Peter; Shigemitsu, Junko; Trottier, Howard; Wingate, Matthew

$B^0_s - \bar{B^0_s}$ Mixing Parameters from Unquenched Lattice QCD

Authors

Dalgic, Emel

Gray, Alan

Gamiz, Elvira

Davies, Christine T. H.

Description

We determine hadronic matrix elements relevant for the mass and width differences, $ΔM_s$ & $ΔΓ_s$ in the $B^0_s - \bar{B^0_s}$ meson system using fully unquenched lattice QCD. We employ the MILC collaboration gauge configurations that include $u$, $d$ and $s$ sea quarks using the improved staggered quark (AsqTad) action and a highly improved gluon action. We implement the valence $s$ quark also with the AsqTad action and use Nonrelativistic QCD for the valence $b$ quark. For the nonperturbative QCD input into the Standard Model expression for $ΔM_s$ we find $f_{B_s} \sqrt{\hat{B}_{B_s}} = 0.281(21)$GeV. Results for four-fermion operator matrix elements entering Standard Model formulas for $ΔΓ_s$ are also presented.
5 pages, version to appear in Physical Review D (Rapid Communications), short section on the width difference $ΔΓ_s$ added