K --> pi pi matrix elements from mixed action lattice QCD

TL;DR

This paper introduces a cost-effective lattice QCD method for calculating K to pi pi matrix elements that improves upon traditional approaches by reducing higher-order corrections, demonstrated with a Delta I=3/2 operator example.

Contribution

A novel lattice QCD technique for determining K to pi pi matrix elements that is less costly and more accurate than previous indirect methods.

Findings

Re(A_2) agrees with experimental value

Total uncertainty of about 20%

Method applicable to various fermion formulations

Abstract

We present a new method for determining K --> pi pi matrix elements from lattice simulations that is less costly than direct simulations of K --> pi pi at physical kinematics. It improves, however, upon the traditional "indirect'' approach of constructing the K --> pi pi matrix elements using NLO SU(3) ChPT, which can lead to large higher-order chiral corrections. Using the explicit example of the Delta I =3/2 (27,1) operator to illustrate the method, we obtain a value for Re(A_2) that agrees with experiment and has a total uncertainty of ~20%. Although our simulations use domain-wall valence quarks on the MILC asqtad-improved gauge configurations, this method is more general and can be applied to calculations with any fermion formulation.