Observation of the singly Cabibbo-suppressed decay $ {\mathrm{\Lambda }}_{c}^{+}\to p{\pi }^{0}$

Utilizing $ 4.5\text{}\text{}{\mathrm{fb}}^{-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})/\mathcal{B}({\mathrm{\Lambda }}_{c}^{+}\to p\eta )=(0.120\pm \phantom{\rule{0ex}{0ex}}0.02{6}_{\mathrm{stat}}\pm 0.00{7}_{\mathrm{syst}})$. 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.