The two-photon contribution to $K_L\to\mu^+\mu^-$ from Lattice QCD

by En-Hung Chao (Columbia University)

Thursday 18 Sep 2025, 09:30 → 10:30 Asia/Shanghai

B105 (CHEP)

Despite its rarity, the decay rate of a long-lived kaon into a pair of muons (KL2MU) has been measured to the percent level. This strangeness-changing process could serve as a precision test of the Standard Model (SM) and a probe to physics beyond due to its sensitivity to physics at high energies. However, it is challenging to make a precise comparison between the SM and experiment because of the sizeable hadronic effects in the long-distance (LD) two-photon-exchange process. In recent years, the RIKEN-Brookhaven-Columbia Collaboration developed a framework enabling to calculate this LD contribution from Lattice Quantum Chromodynamics, which allows for a first-principles SM determination of the KL2MU decay amplitude -- in particular, the interference between the LD and the O($G_F^2$) short-distance contribution. In this talk, I will review this framework and discuss our first numerical results on a physical-pion-mass ensemble at an inverse lattice spacing of 1.023 GeV (arXiv:2509.04346).

Biography: En-Hung Chao is a postdoctoral research associate at the physics department of Columbia University (New York, USA) since 2022. His main research interests are applications of lattice QCD to standard model precision observables. He received his PhD degree from Johannes Gutenberg-University Mainz (Germany), where he contributed to the research group's effort in calculating the hadronic contributions to the anomalous magnetic moment of the muon.