ISSN - 00319007, EISSN - 10797114, Physical Review Letters, 2005, vol. 95, p. -
Improved evidence for direct CP violation in B0→π+π- decays and model-independent constraints on 2
We present a new measurement of the time-dependent CP-violating parameters in B0→π+π- decays with 275×106 BB̄ pairs collected with the Belle detector at the KEKB asymmetric-energy e+e- collider operating at the Υ(4S) resonance. We find 666±43 B0→π+π- events and measure the CP-violating parameters: Sππ=-0.67±0.16(stat)±0. 06(syst) and Aππ=+0.56±0.12(stat)±0.06(syst). We find evidence for large direct CP violation with a significance greater than 4 standard deviations for any Sππ value. Using isospin relations, we obtain 95.4% confidence intervals for the Cabibbo-Kobayashi-Maskawa quark-mixing matrix angle 2 of 0°<2<19° and 71°<2<180°. © 2005 The American Physical Society.