2-PHOTON HELICITY SELECTION-RULES AND WIDTHS FOR POSITRONIUM AND QUARKONIUM STATES WITH ARBITRARY ANGULAR MOMENTA

The observation of a large gamma-gamma width for the 1D2 qqBAR state pi-2(1670) suggests that the gamma-gamma couplings of many orbitally excited light-quark qqBAR states may be experimentally accessible. In this paper we present gamma-gamma helicity amplitudes for nonrelativistic fermion-antifermion states with general angular-momentum quantum numbers 1l(j) and 3l(j), and note some relations and selection rules that may be useful in the spectroscopic classification of orbital excitations.