Year: 2026
Type: preprint
Abstract: We assess the tension between theoretical predictions and the values quoted by the Particle Data Group (PDG) for the partial decay width and branching fraction associated with the radiative charmonium decay $J/ψ\toγη_c$. A profile scan over the most recent PDG data depending on the branching fraction $\mathcal{B}(J/ψ\toγη_c)$ suggests that the correlation between measured branching fractions is compatible with lattice QCD determinations of the partial decay widths $Γ(J/ψ\toγη_c)$ and $Γ(η_c\toγγ)$. We propose a theoretically grounded photon line shape for the radiative decay spectrum and a prescription for the extraction of (product) branching fractions involving the magnetic dipole (M1) transition $J/ψ\toγη_c$. This approach obviates the need to modify the photon energy spectrum line shape using empirical damping functions, as done in the most recent experimental extractions of $\mathcal{B}(J/ψ\toγη_c)$ from the photon line shape, thereby eliminating an inherent ambiguity in the determination of the derived observables.
Source: arXiv (Cornell University)
Authors: Schaaf, Magnus C., Vairo, Antonio
Institution: Technical University of Munich
Language: English
Subfield: Nuclear and High Energy Physics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7165378583