Improving the theoretical prediction for the B_s - B̅_s width difference: matrix elements of next-to-leading order ΔB = 2 operators

¹ SUPA, School of Physics and Astronomy, University of Glasgow, Glasgow G12 8QQ, United Kingdom
² DAMTP, University of Cambridge, Cambridge CB3 0WA, United Kingdom
³ Laboratory of Elementary Particle Physics, Cornell University, Ithaca, NY 14853, United States
⁴ New High Energy Theory Center and Department of Physics and Astronomy, Rutgers, the State University of New Jersey, Piscataway, NJ 08854, United States
⁵ Institute for Nuclear Theory, University of Washington, Seattle, WA 98195-1550, United States
⁶ Department of Physics, Ohio State University, Columbus, Ohio 43210, United States

^* Speaker, e-mail: M.Wingate@damtp.cam.ac.uk

Published online: 26 March 2018

Abstract

We present lattice QCD results for the matrix elements of R₂ and other dimension-7, ΔB = 2 operators relevant for calculations of Δ_s, the B_s - B̅_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 ΔΓ_s will be substantially reduced.