2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/135549We present a precise measurement of the standard model CP-violation parameter sin(2phi1) based on a sample of 152 x 10^6 BB-bar 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 a J/psi Ks0, psi(2S) Ks0, chi_c1 Ks0, eta_c Ks0, J/psi K*0, or J/psi KL CP-eigenstate decay channel and the flavor of the accompanying B meson is identified from its decay products. From the asymmetry in the distribution of the time interval between the two B meson decay points, we obtain sin(2phi1) = 0.733 +/- 0.057(stat) +/- 0.028(syst).11 pages, 4 postscript figures, contributed to the XXI International Symposium on Lepton and Photon Interactions at High Energies, Aug. 11-16, 2003, Fermilab, Illinois USAHigh Energy Physics - Experimenttext