Observation of the Singly Cabibbo-Suppressed Decay Λc⁺→ pπ⁰

This is the authors' abstract. We don't add key points for this paper.

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.