Roper resonance N^*(1440) from charmonium decays

The Roper resonance N^*(1440) was discovered by David Roper in 1964 through sophisticated partial-wave analyses of $πN$ scattering data. However the first direct observation of the Roper resonance peak in the $πN$ invariant mass spectrum was only realized 40 years later from the charmonium decay J/ψ→ pnπ⁺ +c.c. at Beijing Electron-Positron Collider. The further observations of the Roper resonance production from various charmonium decays helped to reveal its multiquark nature with large $σN$ component.