Constrain the decay properties of the ηc

Characterize the decay properties and underlying decay dynamics of the ηc more completely, given that its measured mass and width vary across production mechanisms, its exclusive decay modes account for only about 60% of the total width, and many measurements have large uncertainties.

Background

The paper identifies the ηc as the lowest-lying S-wave spin-singlet charmonium state and notes that its properties are less well constrained than those of the J/ψ. Measurements of its mass and width differ substantially among production mechanisms, including proton–antiproton annihilation, two-photon fusion, B-meson decays, and radiative transitions from ψ(1S,2S).

The paper further notes that only approximately 60% of the total ηc width is accounted for by measured exclusive decay modes and that many existing measurements have large uncertainties. These unresolved experimental and phenomenological issues motivate improved studies of ηc decays, including the long-distance contributions investigated in the paper.