Radiative transitions of charmonium states in the covariant confined quark model

We have studied the dominant radiative transitions of the charmonium S- and P-wave states within the covariant confined quark model. The gauge invariant leading-order transition amplitudes have been expressed by using either the conventional Lorentz structures, or the helicity amplitudes, where it was effective. The renormalization couplings of the charmonium states have been strictly fixed by the compositeness conditions that excludes the constituent degrees of freedom from the space of physical states. We use the basic model parameters for the constituent c-quark mass mc = 1.80 GeV and the global infrared cutoff lambda = 0.181 GeV. We additionally introduce only one adjustable parameter rho 0 common for the charmonium states eta c(1S0), J=psi(3S1), chi c0(3P0), chi c1(3P1), hc(1P1), and chi c2(3P2) to describe the quark distribution inside the hadron. This parameter describes the ratio between the charmonium size and its physical mass. The optimal value rho = 0.485 has been fixed by fitting the latest data for the partial widths of the one-photon radiative decays of the triplet chi cJ(3PJ); J = {0; 1; 2}. Then, we calculate corresponding fractional widths for states J=psi(3S1) and hc(1P1). Estimated results are in good agreement with the latest data. By using the fraction data from PDG2020 and our estimated partial decay width for hc(1P1) we recalculate the theoretical full width ftheor hc <^> (0.57 +/- 0.12) MeV in comparison with latest data fexp hc (boolean AND) (0.7 +/- 0.4) MeV. We also repeated our calculations by gradually decreasing the global cutoff parameter and revealed that the results do not change for any lambda < 0.181 GeV up to the deconfinement limit.

Automated summary

In this study, dominant radiative transitions of charmonium S- and P-wave states were investigated within the covariant confined quark model. Gauge invariant leading-order transition amplitudes were expressed using conventional Lorentz structures or helicity amplitudes, with renormalization couplings of the charmonium states fixed by compositeness conditions. By fitting latest data, an optimal parameter value describing the quark distribution inside hadrons was determined, resulting in estimated results in good agreement with experimental data.