Lattice QCD Matrix Elements for the Bs0 - B ̄ s0 Width Difference beyond Leading Order

Abstract

Predicting the Bs0-B̄s0 width difference ΔΓs 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 R2,3 and linear combinations R2,3 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 ΔΓs using lattice QCD results for all hadronic matrix elements through O(1/mb). The main result of our calculations yields the 1/mb contribution ΔΓ1/mb=-0.022(10) ps-1. Adding this to the leading order contribution, the standard model prediction is ΔΓs=0.092(14) ps-1.