\Delta S=2 and \Delta C=2 bag parameters in the SM and beyond from Nf=2+1+1 twisted-mass LQCD

TL;DR

This paper provides unquenched lattice QCD calculations of four-fermion operator matrix elements relevant for neutral meson mixing, including continuum and physical mass extrapolations, with non-perturbative renormalization.

Contribution

It presents the first unquenched Nf=2+1+1 lattice QCD results for S=2 and C=2 bag parameters, including continuum limit and physical pion mass extrapolations.

Findings

B_K^{RGI} = 0.717(24) for the Kaon bag parameter

Results are extrapolated to continuum and physical pion mass

Non-perturbative renormalization constants determined in RI-MOM scheme

Abstract

We present unquenched lattice QCD results for the matrix elements of four-fermion operators relevant to the description of the neutral K and D mixing in the Standard Model and its extensions. We have employed simulations with Nf = 2 + 1 + 1 dynamical sea quarks at three values of the lattice spacings in the interval 0.06 - 0.09 fm and pseudoscalar meson masses in the range 210 - 450 MeV. Our results are extrapolated to the continuum limit and to the physical pion mass. Renormalization constants have been determined non-perturbatively in the RI-MOM scheme. In particular, for the Kaon bag-parameter, which is relevant for the \overline{K}^0-K^0 mixing in the Standard Model, we obtain B_K^{RGI} = 0.717(24).