Glueballs are predicted by quantum chromodynamics to be massive, despite the fact that gluons themselves have zero rest mass in the Standard Model. Glueballs with all four possible combinations of quantum numbers P (spatial parity) and C (charge parity) for every possible total angular momentum have been considered, producing at least fifteen possible glueball states including excited glueball states that share the same quantum numbers but have differing masses with the lightest states having masses as low as 1.4 GeV/ c (for a glueball with quantum numbers J = 0, P = +1, C = +1, or equivalently J = 0), and the heaviest states having masses as great as almost 5 GeV/ c (for a glueball with quantum numbers J = 0, P = +1, C = −1, or J = 0).