Observation of a rare beta decay of the charmed baryon with a Graph Neural Network
Creators: name: BESIII Collaboration
name: Ablikim, M.
name: Achasov, M. N.
name: Adlarson, P.
name: Afedulidis, O.
name: Ai, X. C.
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Publisher: name: arXiv
Year: 2024
Subjects: subject: High Energy Physics - Experiment (hep-ex)
subject: High Energy Physics - Lattice (hep-lat)
subject: High Energy Physics - Phenomenology (hep-ph)
subject: Nuclear Experiment (nucl-ex)
subject: FOS: Physical sciences
subject: FOS: Physical sciences

description: The beta decay of the lightest charmed baryon $Λ_c^+$ 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 $Λ_c^+ \rightarrow n e^+ ν_{e}$, 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 $Λ_c^+ \rightarrow Λe^+ ν_{e}$, achieving a statistical significance exceeding $10σ$. The absolute branching fraction is measured to be $(3.57\pm0.34_{\mathrm{stat.}}\pm0.14_{\mathrm{syst.}})\times 10^{-3}$. For the first time, the CKM matrix element $\left|V_{cd}\right|$ is extracted via a charmed baryon decay as $0.208\pm0.011_{\rm exp.}\pm0.007_{\rm LQCD}\pm0.001_{τ_{Λ_c^+}}$. 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.
description: 27 pages, 5 figures