  We present an improved measurement of the standard model CP violation
parameter sin2phi1 (also known as sin2beta) based on a sample of 45x10^6 BBbar
pairs collected at the Upsilon(4S) resonance with the Belle detector at the
KEKB asymmetric-energy e+e- collider. One neutral B meson is reconstructed in
the J/psiKS, Psi(2S)KS, chi_c1KS, eta_cKS, J/psiK^*0, or J/psiKL CP-eigenstate
decay channel and the flavor of accompanying B meson is identified from its
decay products. From the asymmetry in the distribution of the time intervals
between the two B meson decay points, we obtain sin2phi1 = 0.82 +/- 0.12(stat)
+/- 0.05(syst). The result is preliminary.
