Rare $K^+ \to \pi^+ \ell^+ \ell^-$ decays with physical mass light-quarks

by Dr Ryan Hill (University of Edinburgh)

Tuesday 16 May 2023, 16:00 → 18:00 Europe/Zurich

4/2-037 - TH meeting room (CERN)

$K^+ \to \pi^+ \ell^+ \ell^-$ is a highly suppressed decay mode in the Standard Model, providing an opportunity to test lepton-flavour universality in the kaon sector, and to find signals of new physics at the precision frontier. The dominant, long-distance contribution to the decay amplitude is non-perturbative in nature, necessitating the use of techniques such as lattice QCD. In this talk, we present the first lattice calculation of the long-distance electromagnetic form factor V at physical light-quark masses for this decay. Our calculation features an explicit GIM subtraction, with dynamical zMöbius quarks and Möbius domain-wall fermion sea-quarks. In order to improve upon the obtained result, we identify the particular challenges to overcome on the road towards a competitive physical-point lattice calculation and suggest routes forward.