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 $4.5{\mathrm{fb}}^{-1}$ 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 $10\sigma$. The absolute branching fraction is measured to be $(3.57\pm 0.34_{stat.}\pm 0.14_{syst.})\times 10^{-3}$. For the first time, the CKM matrix element $\left|V_{cd}\right|$ is extracted via a charmed baryon decay as $0.208\pm 0.011_{exp.}\pm 0.007_{\mathrm{LQCD}}\pm 0.001_{{\tau }_{{\Lambda }_c^{+}}}$. 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.

27 pages, 5 figures

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• ${\Xi }_c\to \Xi$ form factors from lattice QCD with domain-wall quarks: A new piece in the puzzle of ${\Xi }_c^0$ decay rates
• Charm Physics at the Super $\tau$-Charm Factory
• Experimental dataset from BESIII detector at Beijing electron positron collider
• Large CP violation in charmed baryon decays
• Observation of the Singly Cabibbo-Suppressed Decay ${\Lambda }_c^{+}\to p{\pi }^0$
• New opportunities for rare charm from $Z\to c\bar{c}$ decays
• Baryons and baryoniums in the perspective of QCD sum rules