The kaon semileptonic form factor with near physical domain wall quarks

We present a new calculation of the K -> pi semileptonic form factor at zero momentum transfer in domain wall lattice QCD with N-f = 2+1 dynamical quark flavours. By using partially twisted boundary conditions we simulate directly at the phenomenologically relevant point of zero momentum transfer. We perform a joint analysis for all available ensembles which include three different lattice spacings (a = 0.09 - 0.14 fm), large physical volumes (m(pi)L > 3.9) and pion masses as low as 171 MeV. The comprehensive set of simulation points allows for a detailed study of systematic effects leading to the prediction f(+)(K pi)(0) = 0.9670(20)((+18)(-46)), where the first error is statistical and the second error systematic. The result allows us to extract the CKM-matrix element vertical bar V-us vertical bar = 0.2237((+13)(-8)) and confirm first-row CKM-unitarity in the Standard Model at the sub per mille level.