Search for CP-violation in Positronium Decay

TL;DR

This study searches for CP-violation in positronium decay using angular correlations, finding no evidence at a sensitivity level comparable to K meson CP-violation, and setting a more stringent limit on the CP-violation parameter.

Contribution

First experimental search for CP-violation in positronium decay with improved sensitivity and tighter constraints on the CP-violation parameter.

Findings

No CP-violation detected at sensitivity of 2.2×10^{-3}

Set 90% confidence interval for C_CP between -0.0023 and 0.0049

Result improves previous limits by a factor of 7

Abstract

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 (\vec{S}\cdot\vec{k_{1}})(\vec{S}\cdot\vec{k_{1}}\times\vec{k_{2}}), where \vec{S} is the the positronium spin and \vec{k_{1}}, \vec{k_{2}} are the directions of the positronium decay photons. To a sensitivity of 2.2\times10^{-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.