Search for CP violation in ortho-Positronium decay*

The combined charge parity (CP) symmetry violation can only be accommodated in the Standard Model through CP violating phases in the fermion mixing matrices. This has a negligible effect on many processes. Positronium (Ps) is a leptonic state that decays to photons. Observation of CP violation in Ps decay would indicate physics beyond the Standard Model. This has been searched for twice, to 10^-2 and 10^-3 precision. We are designing and constructing a new apparatus to reach 10^-4 precision. The apparatus will consist of a positron source between two fast scintillators for positron detection. The source area is then surrounded with low density powder for Ps formation, all of which is placed inside an array of photon detectors to measure correlations between the decay photons. This will run inside the Positron Polarimeter magnet at FRIB, a superconducting solenoid with a large diameter warm bore, to provide tensor polarized Ps. We present the experimental outline, the design and optimization of the detector array, and the progress on Ps formation. With this design we expect to reach our target sensitivity with 35 days of continuous running.