Neutral B mixing from 2+1 flavor lattice QCD

TL;DR

This paper updates the calculation of B^0-ar{B}^0 mixing matrix elements using 2+1 flavor lattice QCD, employing improved actions and multiple lattice spacings to enhance precision and cover all relevant operators.

Contribution

It provides a more comprehensive analysis of B mixing matrix elements with extended data and discusses the staggered ChPT extrapolation function.

Findings

Calculated hadronic matrix elements for B mixing.

Analyzed SU(3)-breaking ratio xi with extended data.

Covered a full set of five operators for B mixing.

Abstract

We present an update of the Fermilab-MILC Collaboration's calculation of hadronic matrix elements for B^0-\bar{B^0} mixing. This work is a more extended analysis than our recent publication of the SU(3)-breaking ratio xi [arXiv:1205.7013]. We use the asqtad staggered action for light valence quarks in combination 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 spacings 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 ChPT extrapolation function.