Observation of e + e − → χ c 1 at BESIII

In electron-positron annihilations, the process of e + e − → χ c 1 can occur via the production of two virtual photons or through neutral current, therefore being suppressed with respect to the normal annihilation process via one virtual photon. Using a dedicated scan sample around the χ c 1 mass, the direct production of χ c 1 has been established for the first time in experiments. This provides a new approach for the study of the internal nature of hadrons.