Kaon semileptonic vector form factor and determination of|Vus|using staggered fermions

Using staggered fermions and partially twisted boundary conditions, we calculate the K meson semileptonic decay vector form factor at zero momentum transfer. The HISQ formulation is used for the valence quarks, while the sea quarks are simulated with the asqtad action (MILC Nf = 2 + 1 configurations). For the chiral and continuum extrapolation we use two-loop continuum χPT, supplemented by partially quenched staggered χPT at one loop. Our result is f Kπ + (0) = 0.9667 ±