Non-Relativistic QCD for Heavy Quark Systems

We employ a nonrelativistic version of QCD (NRQCD) to study heavy qq̄-bound states in the lowest approximation without fine structure. We use gluon configurations on a 16×48-lattice at β = 6.2 from the UKQCD collaboration. For a bare quark mass near that of the b-quark (Ma = 1.6) we obtain the bound state masses for the S, P and both types of D-waves. We also detect signals for two types of hybrids (qq̄g-states). The results are sufficiently accurate to confirm that the values of the D-wave mass from both D-waves coincide thus indicating that the cubical invariance of the lattice is restored to full rotational invariance to a good approximation. We also study S and P -wave masses for values of the range of bare quark mass Ma = 1.0, 1.3, 1.6 & 1.9 . The results confirm the idea that the S/P -splitting is relatively insensitive to the value of the bare quark mass.