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Observation of the Singly Cabibbo-Suppressed Decay $D^{+}\toωπ^{+}$ and Evidence for $D^{0}\toωπ^{0}$

Based on 2.93 fb$^{-1}$ $e^+e^-$ collision data taken at center-of-mass energy of 3.773 GeV by the BESIII detector, we report searches for the singly Cabibbo-suppressed decays $D^{+}\toωπ^{+}$ and $D^{0}\toωπ^{0}$. A double tag technique is used to measure the absolute branching fractions $\mathcal{B}(D^{+}\toωπ^{+})=(2.79\pm0.57\pm0.16)\times 10^{-4}$ and $\mathcal{B}(D^{0}\toωπ^{0})=(1.17\pm0.34\pm0.07)\times 10^{-4}$, with statistical significances of $5.5σ$ and $4.1σ$, respectively. We also present measurements of the absolute branching fractions for the related $ηπ$ decay modes. We find $\mathcal{B}(D^{+}\toηπ^{+})=(3.07\pm0.22\pm0.13)\times10^{-3}$ and $\mathcal{B}(D^{0}\toηπ^{0})=(0.65\pm0.09\pm0.04)\times10^{-3}$, which are consistent with the current world averages. The first and second uncertainties are statistical and systematic, respectively.