Shedding light on charmonium

We investigate E1 radiative transitions within charmonium in a relativistic approach based on light-front QCD. In quantum field theory, two sets of processes are pure E1: χc0→J/ψγ (ψ→χc0γ) and hc→ηcγ (ηc′→hcγ), both involving the P-wave charmonia. We compute the E1 radiative decay widths as well as the corresponding transition form factors of various processes including those involving 2P states. These observables provide an access to the microscopic structures of the P-wave charmonium. We show that our parameter-free predictions are in excellent agreement with the experimental measurements as well as lattice simulations whenever available. Published by the American Physical Society 2024