Neutral B mixing from 2+1 flavor lattice QCD

We present an update of the Fermilab-MILC Collaboration’s calculation of hadronic matrix ele-ments for B0-B̄0 mixing. This work is a more extended analysis than our recent publication of the SU(3)-breaking ratio ξ [1]. We use the asqtad staggered action for light valence quarks in com-bination with the Fermilab interpretation of the Sheikoleslami-Wohlert action for heavy quarks. The calculations use MILC’s 2+1 flavor asqtad ensembles. Ensembles include four lattice spac-ings from approximately 0.125 fm to 0.045 fm and up/down to strange quark mass ratios as low as 0.05. Our calculation covers the complete set of five operators needed to describe B mixing in the Standard Model and beyond. In addition to an update including a fuller set of analyzed data, we comment on the form of the staggered χPT extrapolation function