We report a measurement of the CP-violating parameters in B0->K0S K0S decays
based on a data sample of 657 million BBbar pairs collected at the Y(4S)
resonance with the Belle detector at the KEKB asymmetric-energy e+e- collider.
In this study, one neutral B meson is fully reconstructed in the B0->K0S K0S
decay mode, and the flavor of the accompanying B meson is identified by its
decay products. The CP-violating parameters are measured from the asymmetry in
the distributions of the proper-time interval between the two B decays: S =
-0.38 +0.69-0.77(stat) +-0.09(syst) and A = -0.38 +-0.38(stat) +-0.05(syst).Comment: 5pages, 2figures, submitted to PR