Precision computation of B_K in quenched lattice QCD

TL;DR

This paper reports a high-precision calculation of the B_K parameter in quenched lattice QCD using Wilson fermions, multiple lattice spacings, and nonperturbative renormalisation, with direct computation at the physical kaon mass in one regularisation.

Contribution

It introduces a novel approach for computing B_K with Wilson fermions, including continuum extrapolation and direct physical mass computation in one regularisation.

Findings

Results show multiplicative renormalisation of the four-fermion operator.

Continuum limit extrapolation achieved across different lattice spacings.

Direct computation at physical kaon mass in one regularisation avoids mass extrapolation.

Abstract

We present the results of a precision computation of B_K with Wilson fermions. Simulations are performed at different lattice spacings, enabling continuum limit extrapolations. Two different twisted mass QCD (tmQCD) regularisations are considered for the computation of bare matrix elements. In both cases the relevant four-fermion operator renormalises multiplicatively. In one regularisation it is possible to perform the computation directly at the physical kaon mass value, thus avoiding extrapolations in the mass. Nonperturbative renormalisation is carried out using available Schroedinger Functional results.