Davies Christine T H, Harrison Judd, Lepage G Peter, Monahan Christopher J, Shigemitsu Junko, Wingate Matthew
SUPA, School of Physics and Astronomy, University of Glasgow, Glasgow, G12 8QQ, United Kingdom.
DAMTP, University of Cambridge, Cambridge CB3 0WA, United Kingdom.
Phys Rev Lett. 2020 Feb 28;124(8):082001. doi: 10.1103/PhysRevLett.124.082001.
Predicting the B_{s}^{0}-B[over ¯]{s}^{0} width difference ΔΓ{s} relies on the heavy quark expansion and on hadronic matrix elements of ΔB=2 operators. We present the first lattice QCD results for matrix elements of the dimension-7 operators R_{2,3} and linear combinations R[over ˜]{2,3} using nonrelativistic QCD for the bottom quark and a highly improved staggered quark (HISQ) action for the strange quark. Computations use MILC Collaboration ensembles of gauge field configurations with 2+1+1 flavors of sea quarks with the HISQ discretization, including lattices with physically light up or down quark masses. We discuss features unique to calculating matrix elements of these operators and analyze uncertainties from series truncation, discretization, and quark mass dependence. Finally we report the first standard model determination of ΔΓ{s} using lattice QCD results for all hadronic matrix elements through O(1/m_{b}). The main result of our calculations yields the 1/m_{b} contribution ΔΓ_{1/m_{b}}=-0.022(10) ps^{-1}. Adding this to the leading order contribution, the standard model prediction is ΔΓ_{s}=0.092(14) ps^{-1}.
预测(B_{s}^{0}-\overline{B}{s}^{0})宽度差(\Delta\Gamma{s})依赖于重夸克展开以及(\Delta B = 2)算符的强子矩阵元。我们给出了对于维度为(7)的算符(R_{2,3})以及线性组合(\widetilde{R}{2,3})的矩阵元的首个格点量子色动力学结果，其中底夸克采用非相对论量子色动力学，奇异夸克采用高度改进的交错夸克（HISQ）作用量。计算使用了MILC合作组的规范场构型系综，其中包含(2 + 1 + 1)味海夸克以及HISQ离散化，包括具有物理上轻的上夸克或下夸克质量的格点。我们讨论了计算这些算符矩阵元所特有的特征，并分析了来自级数截断、离散化以及夸克质量依赖性的不确定性。最后，我们报告了使用格点量子色动力学结果对(\Delta\Gamma{s})进行的首个标准模型确定，该结果涵盖了所有强子矩阵元直至(O(1/m_{b}))阶。我们计算的主要结果给出了(1/m_{b})贡献(\Delta\Gamma_{1/m_{b}} = -0.022(10),\text{ps}^{-1})。将此结果与领头阶贡献相加，标准模型预测为(\Delta\Gamma_{s} = 0.092(14),\text{ps}^{-1})。
