Sea quark effects in B_K from N_f=2 clover-improved Wilson fermions

TL;DR

This paper investigates how sea quark effects influence the B_K parameter in neutral kaon mixing using N_f=2 clover-improved Wilson fermions, highlighting the impact of dynamical quark mass reduction.

Contribution

It provides the first lattice QCD calculation of B_K with dynamical fermions showing dependence on sea quark masses.

Findings

B_K decreases as sea quark masses approach the up/down quark mass.

Evidence of dynamical quark effects on B_K.

Implications for standard model tests and new physics constraints.

Abstract

We report calculations of the parameter B_K appearing in the Delta S=2 neutral kaon mixing matrix element, whose uncertainty limits the power of unitarity triangle constraints for testing the standard model or looking for new physics. We use two flavours of dynamical clover-improved Wilson lattice fermions and look for dependence on the dynamical quark mass at fixed lattice spacing. We see some evidence for dynamical quark effects and in particular B_K decreases as the sea quark masses are reduced towards the up/down quark mass.