Measurement of the CP Violation Parameter sin(2phi_1) in B^0_d Meson Decays

Abstract

We present a measurement of the Standard Model CP violation parameter sin(2phi_1) based on a 10.5 fb^{-1} data sample collected at the Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric e+e- collider. One neutral B meson is reconstructed in the J/psi K_S, psi(2S) K_S, chi_{c1} K_S, eta_c K_S, J/psi K_L or J/psi pi^0 CP-eigenstate decay channel and the flavor of the accompanying B meson is identified from its charged particle decay products. From the asymmetry in the distribution of the time interval between the two B-meson decay points, we determine sin(2phi_1) = 0.58 +0.32-0.34 (stat) +0.09-0.10 (syst).