The Kaon Bag Parameter at Physical Mass

TL;DR

This paper reports a lattice QCD calculation of the Kaon Bag parameter $B_K$ at physical meson masses, avoiding chiral extrapolation, and compares the results with previous studies to analyze uncertainties.

Contribution

It provides a direct lattice QCD computation of $B_K$ at physical masses using M"obius Domain Wall Fermions, with non-perturbative renormalization and comparison to prior results.

Findings

Preliminary $B_K$ value at physical mass obtained.

Renormalization performed via Rome-Southampton technique.

Comparison indicates dominant error sources.

Abstract

We present preliminary results for the calculation of the Kaon Bag parameter $B_K$ in $N_f=2+1$ lattice QCD, using M\"obius Domain Wall Fermion ensembles generated by the RBC-UKQCD collaboration. This computation is done directly at physical meson masses, so that we do not have to rely on chiral perturbation theory or any other mass extrapolation. In parallel, the four-quark operator is renormalised through the Rome-Southampton technique. Finally, we compare our value with previous results and draw some conclusions about the remaining dominant contributions in our error budget.