Improving the theoretical prediction for the $B_s-\bar{B}_s$ width difference: matrix elements of next-to-leading order $\Delta B=2$ operators

TL;DR

This paper reports lattice QCD calculations of matrix elements for dimension-7 operators relevant to the $B_s$ meson width difference, aiming to improve the precision of Standard Model predictions.

Contribution

It provides new lattice QCD results for $ ext{Δ}B=2$ operators, reducing theoretical uncertainties in $ ext{Δ} ext{Γ}_s$ calculations.

Findings

Computed matrix elements using 5 gauge ensembles.

Reduced uncertainty in Standard Model prediction for $ ext{Δ} ext{Γ}_s$.

Used HISQ and NRQCD actions for valence quarks.

Abstract

We present lattice QCD results for the matrix elements of $R_2$ and other dimension-7, $\Delta B = 2$ operators relevant for calculations of $\Delta \Gamma_s$, the $B_s-\bar{B}_s$ width difference. We have computed correlation functions using 5 ensembles of the MILC Collaboration's 2+1+1-flavour gauge field configurations, spanning 3 lattice spacings and light sea quarks masses down to the physical point. The HISQ action is used for the valence strange quarks, and the NRQCD action is used for the bottom quarks. Once our analysis is complete, the theoretical uncertainty in the Standard Model prediction for $\Delta \Gamma_s$ will be substantially reduced.