Branching-ratio measurements of multiphoton decays of positronium

Positronium (Ps) decay to four- and five-photon final states has been measured. From a sample of 3.73x10{sup 9} detected events of Ps annihilation, the QED-allowed branching ratios of para-Ps to four photons R{sub 4}=1.14(33)(21)x10{sup -6} (stat., sys., 68% C.L.), and ortho-Ps to five photons R{sub 5}=1.67(99)(37)x10{sup -6} (68% C.L.) were measured. No charge-conjugation symmetry violating events were observed, establishing a branching ratio limit for (o-Ps{yields}4{gamma}) of R{sub 4}{sup Ce}