A comprehensive determination of the rich, low-lying spectrum of gluonic excitations in the
presence of a static quark-antiquark pair is presented. Our results are obtained from several
simulations on anisotropic lattices using an improved action and a large set of gluonic
operators. The hybrid quarkonium states are studied in the quenched approximation using
the Born-Oppenheimer expansion and nonrelativistic lattice QCD.

The spectrum of gluon excitations in the presence of a static quark-antiquark pair is
presented. Our results are obtained from computer simulations of gluons on anisotropic
space-time lattices using an improved gauge-field action. Measurements for quark-antiquark
separations r ranging from 0.1 fm to 4 fm and for various orientations on the lattice are made.
Discretization errors and finite volume effects are taken into account. Surprisingly, the
spectrum does not exhibit the expected onset of the universal π/r Goldstone excitations of …