Search for CP Violation in Positronium Decay

CP violation in the quark sector has been well established over the last decade, but has not been observed in the lepton sector. We search for CP violating decay processes in positronium, using the angular correlation of ((S) over right arrow . (k) over right arrow (1)) ((S) over right arrow . (k) over right arrow (1) X (k) over right arrow (2)), where (S) over right arrow is the positronium spin and (k) over right arrow (1), (k) over right arrow (2) are the directions of the positronium decay photons. To a sensitivity of 2.2 x 10(-3), no CP violation has been found, which is at the level of the CP violation amplitude in the K meson. A 90% confidence interval of the CP violation parameter (C-CP) was determined to be -0:0023 < C-CP < 0:0049. This result is a factor 7 more strict than that of the previous experiment.