Ryan Hill, Edinburgh, [HET Seminar] Rare K->pi l+ l- decays from lattice QCD at the physical point

Thursday 4 Dec 2025, 11:00 → 13:00 US/Eastern

Small Seminar Room

Rare kaon decays are highly-suppressed decay modes in the Standard Model, and can serve as a laboratory for precision tests of new physics in the kaon sector. At low energy, the amplitudes of the rare K^+->pi^+ l+l- and K_S->pi^0 l+l- decays are described by the parameters 'a' and 'b', for which there are multiple outstanding puzzles. In particular, there is substantial disagreement between experiment and theory for a^+, and an experimental measurement of the K_L -> pi0 l+ l- amplitude  at KOTO II is highly sensitive to the sign of a_S. Over the last ten years, lattice QCD calculations have explored prospects for a first-principles solution to these challenges. The current physical-point lattice result of a^+=-0.87(4.44) is unresolved, due to a large noise contribution from stochastically estimating GIM loops at physical masses. Here we present progress on an updated calculation that exploits frequency-splitting estimators to obtain at least an order-of-magnitude reduction in the GIM loop noise, and even greater improvements on specific critical contributions.

 

https://bnl.zoomgov.com/j/16010362754?pwd=Z1l1SS9JUDlyR1hSUHNyaDV1dTZHUT09