Updated Measurement of phi_3 with a Dalitz Plot Analysis of B->D(*)K Decay

Abstract

We present an updated measurement of the unitarity triangle angle phi_3 using a Dalitz plot analysis of the K^0_S pi+ pi- decay of the neutral D meson produced in B+- ->D(*)K+- decays. The method exploits the interference between D^0 and Dbar^0 to extract the angle phi_3, strong phase delta and the ratio r of suppressed and allowed amplitudes. We apply this method to a 605 fb-1 data sample collected by the Belle experiment. The analysis uses two modes: B+- -> DK+-, and B+- -> D*K+- with D* -> D pi0, as well as the corresponding charge-conjugate modes. From a combined maximum likelihood fit to the two modes, we obtain phi_3=76+12-13(stat)+-4(syst)+-9(model). The statistical significance of CP violation (phi_3\neq 0) in our measurement is (1-5.5*10^{-4}), or 3.5 standard deviations. These results are preliminary.