Hyperspherical-coordinate approach to the spectra and decay widths of hybrid quarkonia

In this paper, we consider the possibility that Y(4260), Y(4360), ψ (4415 ), or X(4660) is the ground state or the first excited state of a hybrid charmonium and examine whether ϒ (10860 ) is the ground state or the first excited state of a hybrid bottomonium. Under a constituent quark model, we carry out numerical calculations to obtain the spectra of both electric gluon and magnetic gluon hybrid quarkonia. We see that the ground state of a magnetic gluon hybrid charmonium and the first excited state of an electric gluon hybrid are comparable in energy to ψ (4415 ) and that the first excited states of an electric gluon hybrid bottomonium and the ground state of a magnetic gluon hybrid appear a few hundred MeV above the mass of ϒ (10860 ). Also, we evaluate the widths of the decays of a hybrid charmonium into D^(*)D^{¯ (*)} and those of a hybrid bottomonium into B^(*)B^¯(*). We show that if the exotic meson candidates are hybrid charmonia, then they are magnetic gluon ones and argue that it seems unlikely that ϒ (10860 ) is the ground state of an electric gluon hybrid bottomonium.