Observation of the Singly Cabibbo-Suppressed Decay ${\mathrm{\Lambda }}_c^{+}\to p{\pi }^0$

Utilizing 4.5${\mathrm{f}\mathrm{b}}^{-1}$ of $e^{+}{e}^{-}$ annihilation data collected with the BESIII detector at the BEPCII collider at center-of-mass energies between 4.600 and 4.699 GeV, the first observation of the singly Cabibbo-suppressed decay ${\mathrm{\Lambda }}_c^{+}\to p{\pi }^0$ is presented, with a statistical significance of $5.4\sigma$. The ratio of the branching fractions of ${\mathrm{\Lambda }}_c^{+}\to p{\pi }^0$ and ${\mathrm{\Lambda }}_c^{+}\to p\eta$ is measured as $\mathcal{B}({\mathrm{\Lambda }}_c^{+}\to p{\pi }^0)\mathrm{/}\mathcal{B}({\mathrm{\Lambda }}_c^{+}\to p\eta )=(0.120\pm {0.026}_{\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{t}\mathrm{.}}\pm {0.007}_{\mathrm{s}\mathrm{y}\mathrm{s}\mathrm{t}\mathrm{.}})$. This result resolves the longstanding discrepancy between earlier experimental searches, providing both a decisive conclusion and valuable input for QCD-inspired theoretical models. A sophisticated deep learning approach using a Transformer-based architecture is employed to distinguish the signal from the prevalent hadronic backgrounds, complemented by thorough validation and systematic uncertainty quantification.