Observation of a rare beta decay of the charmed baryon with a Graph Neural Network

Abstract

The beta decay of the lightest charmed baryon ${\Lambda }_c^{+}$ provides unique insights into the fundamental mechanism of strong and electro-weak interactions, serving as a testbed for investigating non-perturbative quantum chromodynamics and constraining the Cabibbo-Kobayashi-Maskawa (CKM) matrix parameters. This article presents the first observation of the Cabibbo-suppressed decay ${\Lambda }_c^{+}\to n{e}^{+}{\nu }_e$ , utilizing 4.5 fb^-1 of electron-positron annihilation data collected with the BESIII detector. A novel Graph Neural Network based technique effectively separates signals from dominant backgrounds, notably ${\Lambda }_c^{+}\to \Lambda e^{+}{\nu }_e$ , achieving a statistical significance exceeding 10σ. The absolute branching fraction is measured to be (3.57 ± 0.34_stat. ± 0.14_syst.) × 10^-3. For the first time, the CKM matrix element $\left(V_{cd}\right)$ is extracted via a charmed baryon decay as $0.208\pm 0.011_{\mathrm{exp.}}\pm 0.007_{\mathrm{LQCD}}\pm 0.001_{{\tau }_{{\Lambda }_c^{+}}}$ . This work highlights a new approach to further understand fundamental interactions in the charmed baryon sector, and showcases the power of modern machine learning techniques in experimental high-energy physics.