Lattice QCD matrix elements for the ${B_s^0-\bar{B}_s^0}$ width difference beyond leading order

TL;DR

This paper presents the first lattice QCD calculations of matrix elements for higher-dimension operators relevant to the $B_s^0-ar{B}_s^0$ width difference, enabling a more precise Standard Model prediction of $ riangle ext{Gama}_s$.

Contribution

It introduces novel lattice QCD results for dimension-7 operators and incorporates these into the first comprehensive Standard Model prediction of $ riangle ext{Gama}_s$ beyond leading order.

Findings

First lattice QCD results for dimension-7 operators $R_{2,3}$ and $ ilde{R}_{2,3}$.

Standard Model prediction of $ riangle ext{Gama}_s = 0.092(14)~ ext{ps}^{-1}$.

Quantified uncertainties from series truncation, discretization, and quark mass dependence.

Abstract

Predicting the $B_s^0-\bar{B}_s^0$ width difference $\Delta\Gamma_s$ relies on the heavy quark expansion and on hadronic matrix elements of $\Delta B=2$ operators. We present the first lattice QCD results for matrix elements of the dimension-7 operators $R_{2,3}$ and linear combinations $\tilde{R}_{2,3}$ using nonrelativistic QCD for the bottom quark and a highly improved staggered quark (HISQ) action for the strange quark. Computations use MILC ensembles of gauge field configuations with $2+1+1$ flavors of sea quarks with the HISQ discretization, including lattices with physically light up/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 $\Delta\Gamma_s$ using lattice QCD results for all hadronic matrix elements through $\mathcal{O}(1/m_b)$. The main result of our calculations yields the $1/m_b$ contribution $\Delta \Gamma_{1/m_b} = -0.022(10)~\mathrm{ps}^{-1}$. Adding this to the leading order contribution, the Standard Model prediction is $\Delta \Gamma_s = 0.092(14)~\mathrm{ps}^{-1}$.