Finite-size effects for lattice glueball masses

We have measured the lattice size dependence of the lightest glueball mass in SU(2) and SU(3) gauge theory at {β}=2.2 and 2.3 [SU(2)] and {β}=6.0 [SU(3)]. We observe an increase in the glueball mass when the lattice size shrinks below a critical value. The magnitude of this length scale, which we interpret as the physical size of the glueball, is roughly the same for SU(2) and SU(3) when expressed in units of the string tension.