A lattice computation of the first moment of the kaon's distribution amplitude

We present a lattice computation of the first moment of the kaon's leading-twist distribution amplitude. The results were computed using ensembles with 2 + I dynamical flavours with the domain wall fermion action and Iwasaki gauge action from the RBC and UKQCD joint dataset. The first moment is non-zero because of SU(3)-breaking effects, and we find that we are able to measure these effects very clearly. We observe the expected chiral behaviour and finally obtain (xi) (2 GeV) =3/5a(K)(1) (2 GeV) = 0.032(3), which agrees very well with results obtained using sum rules, but with a significantly smaller error. We discuss the systematic uncertainties in detail and explain the prospects for their further reduction. In particular. we are implementing a programme of non-perturbative renormalization to improve the precision on the normalization of the lattice operators (currently performed perturbatively) and are repeating the calculation on a large lattice (24(3) x 64 as compared to the present 16(3) x 32 lattice). (c) 2006 Elsevier B.V. All rights reserved.