Tests of CP and CPT symmetry with positronium

Abstract

The 3γ decay of spin‐aligned triplet positronium can be used to test CP (C = charge conjugation, and P = parity operation) invariance in the lepton sector. The angular correlation (ŝ⋅k̂1)(ŝ⋅k̂1×k̂2) is used for this test, where s is the positronium spin and |k1|>|k2|>|k3| are the γ momenta.We designed a new detector to test this symmetry at the 10−3 level. This detector consists of a magnet, a β+ tagging and o‐Ps creation system, γ‐ray detectors, and a turntable. The detector construction is almost finished and data acquisition will begin in this spring.With a similar detector, the CPT (T = time reversal) symmetry can be also tested. In this case, the angular correlation (ŝ⋅k̂1×k̂2) is used. This test will be started after the CP test is finished.