Two-photon contribution to the $K_L\to\mu^+\mu^-$ decay amplitude from a $1/a\approx 1 $ GeV lattice

TL;DR

This paper reports a lattice-QCD calculation of the long-distance two-photon contribution to the $K_L o\mu^+\mu^-$ decay amplitude, focusing on reducing statistical uncertainties in the results.

Contribution

First lattice-QCD calculation of the long-distance two-photon contribution to this decay, with strategies to improve statistical precision.

Findings

Preliminary results for most diagrams except quark-line disconnected ones.

Intermediate $\eta ext{-}$contribution identified as largest uncertainty.

Strategies to reduce statistical errors are proposed and discussed.

Abstract

We present a lattice-QCD calculation of the long-distance two-photon contribution to the decay amplitude of a long-lived kaon to a pair of muons on a $24^3\times 64$ physical-pion-mass ensemble. In these proceedings, the theoretical foundation of this calculation will be reviewed and preliminary numerical results will be presented for all diagrams with the exception of those that are quark-line disconnected SU(3)-flavor-suppressed. At this stage, the intermediate $\eta$ contribution appears to be the largest source of statistical uncertainty. Our proposed strategies to reduce these statistical errors are discussed in great detail.