  In the last decade, lattice QCD has been able to compute the low-lying
glueball spectrum with accuracy. Like other effective approaches of QCD,
potential models still have difficulties to cope with gluonic hadrons. Assuming
that glueballs are bound states of valence gluons with zero current mass, it is
readily understood that the use of a potential model, intrinsically non
covariant, could be problematic in this case. The main challenge for this kind
of model is actually to find a way to introduce properly the more relevant
degree of freedom of the gluon: spin or helicity. In this work, we use the
so-called helicity formalism of Jacob and Wick to describe two-gluon glueballs.
We show in particular that this helicity formalism exactly reproduces the
$J^{PC}$ numbers which are observed in lattice QCD when the constituent gluons
have a helicity-1, without introducing extra states as it is the case in most
of the potential models. These extra states appear when gluons are seen as
spin-1 particles. Using a simple spinless Salpeter model with Cornell potential
within the helicity formalism, we obtain a glueball mass spectrum which is in
good agreement with lattice QCD predictions for helicity-1 gluons provided
instanton-induced interactions are taken into account.
