Search for CP-Violation in ortho-Positronium Decay

The combined charge and parity (CP) transformation is an exact symmetry in QED. Within the Standard Model only small amounts of CP-violation are generated in processes involving quark mixing and possibly neutrino mixing. Positronium is an electromagnetically bound state of an electron and a positron, and as such is insensitive to any Standard Model CP-violation. We are carrying out an experiment to search for a CP-violating angular correlation in the decay photons of positronium, that could only be induced by beyond Standard Model physics [1]. Our goal is a tenfold increase in sensitivity over previous searches [2-3].



We will present the design, construction, and testing of a dedicated gamma detector array that fits within a superconducting solenoid magnet at the Facility for Rare Isotope Beams. We also report on progress on a positronium formation cell and fast scintillators for positron tagging. With our setup we expect to reach the target sensitivity with one month of continuous runtime.



[1] W. Bernreuther, U. Löw, J.P. Ma, et al. Z. Phys. C - Particles and Fields 41, 143–158 (1988).

[2] M. Skalsey and J. Van House, Phys. Rev. Lett. 67 (1993)

[3] T. Yamazaki, T. Namba, S. Asai, T. Kobayashi, Phys. Rev. Lett. 104 (2010)