QCD string in excited heavy-light mesons and heavy-quark hybrids

The QCD string model is employed to evaluate the masses of orbitally and radially excited heavy-light mesons and lightest hybrids in the spectrum of charmonium and bottomonium. The number of parameters of the model is reduced to only seven which are the string tension, the two values of the strong coupling constant (one for heavy-light and $\overline{c}c$ mesons and one for $\overline{b}b$ mesons), and the four overall spectrum shift constants which depend on the quark contents of the particular meson or hybrid family. A few well-established states in the spectrum of heavy-light and heavy-heavy mesons are used to fix these parameters, and then the masses of other mesons and hybrids come out as predictions of the model which are confronted with the existing experimental data, and a few suggestions are made concerning yet not measured quantum numbers of some states in the spectrum of charmonium and bottomonium.

Figure 1

The mixing angle $\theta$ for the $P$ levels as a function of the inversed heavy-quark mass. The physical points for the $b$ and $c$ quarks are shown with vertical dotted lines.