Delta I=3/2 K to pi-pi decays with nearly physical kinematics

TL;DR

This paper presents a lattice QCD calculation of the a/2 K to pi pi decay amplitude near physical kinematics, providing key results for understanding CP violation and the a/2 decay process within the Standard Model.

Contribution

The study performs a near-physical lattice QCD calculation of the a/2 decay amplitude using domain wall fermions, including reweighting analysis for partial quenching effects, which is a novel approach in this context.

Findings

Re(A_2) = (1.436 b1 0.063_{stat} b1 0.258_{syst}) d7 10^-8 GeV

Im(A_2) = (-6.29 b1 0.46_{stat} b1 1.20_{syst}) d7 10^-13 GeV

Predicted Im(A_0) = -5.32(64)_{stat}(71)_{syst} d7 10^-11 GeV

Abstract

The \Delta I = 3/2 K to pi pi decay amplitude is calculated on RBC/UKQCD 32^3 times 64, L_s=32 dynamical lattices with 2+1 flavours of domain wall fermions using the Dislocation Suppressing Determinant Ratio and Iwasaki gauge action. The calculation is performed close to the physical pion mass (m_pi = 142.9(1.1) MeV and with a single lattice spacing (a^-1= 1.375(9) GeV.) We find Re(A_2) = (1.436 \pm 0.063_{stat} \pm 0.258_{syst}) times 10^-8 GeV and Im(A_2) = (-6.29 \pm 0.46_{stat} \pm 1.20_{syst})\times 10^{-13} GeV. These results are combined with the experimental result for epsilon'/epsilon to predict Im(A_0) = -5.32(64)_{stat}(71)_{syst}\times 10^{-11} GeV within the Standard Model. We also perform a reweighting analysis to investigate the effects of partial quenching in the light-quark sector of our calculation. Following reweighting we find Re(A_2) = (1.52\pm 0.14_{stat}) \times 10^-8 GeV and Im(A_2) = (-6.47 \pm 0.55_{stat})\times 10^-13 GeV, which are consistent with our main results.