Measurement of the CP Violation Parameter sin2φ1 in B0d Meson Decays

We present a measurement of the standard model CP violation parameter sin2φ₁ (also known as sin2β) based on a 10.5 fb^-1 data sample collected at the ϒ\(4S\) resonance with the Belle detector at the KEKB asymmetric e⁺e^- collider. One neutral B meson is reconstructed in the J/ψK_S, ψ\(2S\)K_S, χ_c1K_S, η_cK_S, J/ψK_L, or J/ψπ⁰ 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 sin2φ₁ = 0.58^+0.32_-0.34\(stat\)^+0.09_{- 0.10}\(syst\).