[NT/RBRC hybrid seminar] $K_L\rightarrow\mu^+\mu^-$ from lattice QCD

by Dr En-Hung Chao (Columbia University)

Friday 8 Sept 2023, 11:00 → 13:00 US/Eastern

Large Seminar Room (https://bnl.zoomgov.com/j/1614715193?pwd=WkwxODVWdzZzb29zQnZRVGp3VTBDQT09)

In this talk, I will discuss the applicability of lattice QCD to the long-distance (LD) two-photon contribution to the decay of a long-lived neutral kaon into a charged-muon pair (KL2mu), where the two final-state muons are directly coupled to the two photons. Despite its rareness, the established experimental KL2mu decay rate is known to 1.6 percent, which makes it an appealing precision probe of the Standard Model. In particular, the knowledge of the short-distance (SD) contribution due to the exchange of two W-bosons or a W- and a Z-bosons will further constrain the unitarity triangle and distinguish possible scenarios for physics beyond the Standard Model. Nonetheless, the LD two-photon process turns out to contribute significantly to the absorptive part of the KL2mu decay amplitude. In order to make a sensible comparison to the experiment, the dispersive part due to the LD two-photon process, which interferes with the SD contribution, needs to be determined to a good precision from the theory side.

In our work, we propose to compute the complex LD two-photon amplitude with a lattice-QCD-based formalism. Especially, the experimentally inaccessible dispersive part can be calculated from first principles within this framework.