Observation of the doubly Cabibbo-suppressed decays D + → K + π 0 π 0 and D + → K + π 0 η

By analyzing e + e − annihilation data corresponding to an integrated luminosity of 2.93 fb −1 collected at the center-of-mass energy of 3.773 GeV with the BESIII detector, we report the first observations of the doubly Cabibbo-suppressed decays D + → K + π 0 π 0 and D + → K + π 0 η. The branching fractions of D + → K + π 0 π 0 and D + → K + π 0 η are measured to be (2.1 ± 0.4stat ± 0.1syst) × 10 −4 and (2.1 ± 0.5stat ± 0.1syst) × 10 −4 with statistical significances of 8.8σ and 5.5σ, respectively. In addition, we search for the subprocesses D + → K *(892)+ π 0 and D + → K *(892)+ η with K *(892)+ → K + π 0. The branching fraction of D + → K *(892)+ η is determined to be ( ${4.4}_{-{1.5}_{\text{stat}}}^{+1.8}$ ± 0.2syst) × 10 −4, with a statistical significance of 3.2σ. No significant signal for D + → K *(892)+ π 0 is found and we set an upper limit on the branching fraction of this decay at the 90% confidence level to be 5.4 × 10 −4.