Measurement of the branching fraction and CP asymmetry of B0→π0π0 decays using 198×106 BB ̄ pairs in Belle II data

We report measurements of the branching fraction and CP asymmetry in B0→π0π0 decays reconstructed at Belle II in an electron-positron collision sample containing 198×106 B ̄B pairs. We measure a branching fraction B(B0→π0π0)=(1.38±0.27±0.22)×10−6 and a CP asymmetry ACP(B0→π0π0)=0.14±0.46±0.07, where the first uncertainty is statistical and the second is systematic.