Abstract
We present lattice QCD results for the matrix elements of R2 and other dimension-7, ΔB = 2 operators relevant for calculations of Δs, the Bs - B̅s 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 ΔΓs will be substantially reduced.
Highlights
Mixing between particle and antiparticle states of neutral mesons has been observed in K0, D0, B0, and B0s mesons
For the B0s system these parameters are constrained by experimental measurements of the B0s-B0s mass difference, width difference, and a flavour-specific
The contributions from charm and up quarks in the intermediate states depend on the corresponding CKM matrix elements; i.e. Γ1s2 = −(λ2cΓc1c2 + 2λcλuΓu1c2 + λ2uΓu1u2) with λi = Vi∗sVib
Summary
Mixing between particle and antiparticle states of neutral mesons has been observed in K0, D0, B0, and B0s mesons. The contributions from charm and up quarks in the intermediate states depend on the corresponding CKM matrix elements; i.e. Γ1s2 = −(λ2cΓc1c2 + 2λcλuΓu1c2 + λ2uΓu1u2) with λi = Vi∗sVib. At the present level of accuracy, only the CKM-leading contribution from Γc1c2 is important. Direct lattice QCD calculation of matrix elements such as Bs|T |Bs is not generally feasible due to the difficulty in correctly treating all intermediate states.1 one can employ an operator product expansion known as the heavy quark expansion (HQE).
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