The light quarkonium and charmonium mass shifts in an unquenched quark model

Abstract The unquenched quark model for the light quarkonium and charmonium states is explored in this study. The quark-pair creation operator in the model, which combines the two-quark and four-quark components, is modified by considering the effects of the created quark pair's energy. Furthermore, the separation between the created quark pair and valence quark pair is modified. All the wave functions, including those for the mesons and the relative motion between two mesons, are obtained by solving the corresponding Schrödinger equation using the Gaussian expansion method. The aim of this study is to find a new set of parameters that can accurately describe the mass spectrum of low-lying light quarkonium and charmonium states. Moreover, certain exotic states, such as , can be described well in the unquenched quark model.