We present a new calculation of the first Gegenbauer moment $a_1^K$ of the kaon light cone distribution amplitude. This moment is determined by the difference between the average momenta of strange and nonstrange valence quarks in the kaon. To calculate $a_1^K$, QCD sum rule for the diagonal correlation function of local and nonlocal axial-vector currents is used. Contributions of condensates up to dimension six are taken into account, including $O({\alpha }_s)$-corrections to the quark-condensate term. We obtain $a_1^K=0.05\pm 0.02$, differing by the sign and magnitude from the recent sum rule estimate from the nondiagonal correlation function of pseudoscalar and axial-vector currents. We argue that the nondiagonal sum rule is numerically not reliable. Furthermore, an independent indication for a positive $a_1^K$ is given, based on the matching of two different light cone sum rules for the $K\to \pi$ form factor. With the new interval of $a_1^K$, we update our previous numerical predictions for SU(3)-violating effects in $B_{(s)}\to K$ form factors and charmless $B$ decays.

• Received 30 July 2004

DOI:https://doi.org/10.1103/PhysRevD.70.094002