Neutral B-meson mixing parameters in and beyond the SM with 2+1 flavor lattice QCD

TL;DR

This paper presents a lattice QCD calculation of neutral B-meson mixing parameters, including all relevant operators, with a comprehensive analysis of systematic uncertainties to improve understanding of flavor physics beyond the Standard Model.

Contribution

The study provides the first comprehensive lattice QCD calculation of all five operators contributing to B-meson mixing in and beyond the Standard Model, using multiple lattice spacings and light quark masses.

Findings

Calculated matrix elements for all five operators involved in B-meson mixing.

Performed a combined chiral-continuum extrapolation including wrong-spin effects.

Provided a detailed systematic error budget for the results.

Abstract

We report on the status of our calculation of the hadronic matrix elements for neutral $B$-meson mixing with asqtad sea and valence light quarks and using the Wilson clover action with the Fermilab interpretation for the $b$ quark. We calculate the matrix elements of all five local operators that contribute to neutral $B$-meson mixing both in and beyond the Standard Model. We use MILC ensembles with $N_f=2+1$ dynamical flavors at four different lattice spacings in the range $a \approx 0.045$--$0.12$~fm, and with light sea-quark masses as low as 0.05 times the physical strange quark mass. We perform a combined chiral-continuum extrapolation including the so-called wrong-spin contributions in simultaneous fits to the matrix elements of the five operators. We present a complete systematic error budget and conclude with an outlook for obtaining final results from this analysis.