Guan Y.PAO-TI CHANGet. al.2024-10-232024-10-232024-08-22https://scholars.lib.ntu.edu.tw/handle/123456789/722346We present a comprehensive study of B0→ωω decays using 772×106 BB¯ pairs collected with the Belle detector at the KEKB e+e- collider. This process is a suppressed charmless decay into two vector mesons and can exhibit interesting polarization and CP violation. The decay is observed for the first time with a significance of 7.9 standard deviations. We measure a branching fraction B=(1.53±0.29±0.17)×10-6, a fraction of longitudinal polarization fL=0.87±0.13±0.13, and a time-integrated CP asymmetry ACP=-0.44±0.43±0.11, where the first uncertainties listed are statistical and the second are systematic. This is the first observation of B0→ωω and the first measurements of fL and ACP for this decay.journal article10.1103/PhysRevLett.133.081801