Observation of the singly Cabibbo-suppressed decay Λc+ →pπ0

Utilizing 4.5 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 Λc+→pπ0 is presented, with a statistical significance of 5.4σ. The ratio of the branching fractions of Λc+→pπ0 and Λc+→pη is measured as B(Λc+→pπ0)/B(Λc+→pη)=(0.120±0.026stat±0.007syst). 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.