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

Abstract

Utilizing 4.5${~\rm{fb}}^{-1}$ 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 $\Lambda_c^{+}\to p\pi^0$ is presented, with a statistical significance of $5.4\sigma$. The ratio of the branching fractions of $\Lambda_c^{+}\to p\pi^0$ and $\Lambda_c^{+}\to p\eta$ is measured as $\mathcal{B}(\Lambda_c^{+}\to p\pi^0)/\mathcal{B}(\Lambda_c^{+}\to p\eta)=(0.120\pm0.026_{\rm stat.}\pm0.007_{\rm syst.})$. 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.