Kaon semileptonic decays near the physical point

Abstract

The CKM matrix element |V us | can be extracted from the experimental measurement of semileptonic K → π decays. The determination depends on theory input for the corresponding vector form factor in QCD. We present a preliminary update on our efforts to compute it in N f = 2 + 1 lattice QCD using domain wall fermions for several lattice spacings and with a lightest pion mass of about 170 MeV. By using partially twisted boundary conditions we avoid systematic errors associated with an interpolation of the form factor in momentum-transfer, while simulated pion masses near the physical point reduce the systematic error due to the chiral extrapolation.