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sin2phi1 with 45 Million BBbar Pairs at Belle

Masashi Hazumi

hep-exarXiv:hep-ex/0207075

Abstract

We present an improved measurement of the standard model CP violation parameter sin2phi1 (also known as sin2beta) based on a sample of 45 x 106 BBbar pairs collected at the Upsilon(4S) resonance with the Belle detector at the KEK asymmetric-energy e+e- collider. One neutral B meson is reconstructed in a J/psi Ks, psi(2s) Ks, chic1 Ks, etac Ks, J/psi K*, or J/psi KL 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).

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