Angular-correlation test of<i>CPT</i>in polarized positronium

Abstract

Polarized triplet positronium, formed in the ground state with a polarized slow-${e}^{+}$ beam, is used for an experimental test of CPT (charge-conjugation--parity--time-reversal) invariance. The angular correlation S^\ensuremath{\cdot}k${^}_{1}$\ifmmode\times\else\texttimes\fi{}k${^}_{2}$ was measured (where S is the positronium spin angular momentum and \ensuremath{\Vert}${\mathrm{k}}_{1}$\ensuremath{\Vert}&gt;\ensuremath{\Vert}${\mathrm{k}}_{2}$\ensuremath{\Vert}&gt;\ensuremath{\Vert}${\mathrm{k}}_{3}$\ensuremath{\Vert} are the momenta of the three decay \ensuremath{\gamma} rays). It is expected to have zero amplitude if CPT is conserved. No effect was found in the experiment at the 2.3% level of uncertainty in the coefficient of the angular correlation. Information gained from a study of the systematic effects, along with straightforward improvements in the apparatus, would allow a 0.1% measurement. Other possible angular correlations using polarized and aligned positronium, including tests of CP invariance, are discussed.