  We present first results from the QCDSF collaboration for the kaon
semileptonic decay form factors at zero momentum transfer, using two flavours
of non-perturbatively O(a)-improved Wilson quarks. A lattice determination of
these form factors is of particular interest to improve the accuracy on the CKM
matrix element |V_us|. Calculations are performed on lattices with lattice
spacing of about 0.08 fm with different values of light and strange quark
masses, which allows us to extrapolate to chiral limit. Employing double ratio
techniques, we are able to get small statistical errors.

High Energy Physics - Lattice