Chinese Acad Sci, Inst High Energy Phys, Beijing 100049, Peoples R China
; Chinese Acad Sci, Inst Theoret Phys, Beijing 100080, Peoples R China
Relativistic effects in two-photon decay of quarkonium are investigated with a relativistic phenomenological approach. Compared with the NR approximation usually used, the relativistic phenomenological approach gives corrections coming from three sources: q (q) over bar relative momentum distribution, q (q) over bar relative energy distribution and description of quark spinors in the meson. These relativistic effects are studied in detail for m and ss systems.