Abstract
The radiative decay η→ππγ can be a probe of new physics that violates charge conjugation (C) and time reversal (T) symmetries. We discuss the measurements required to facilitate such observations. We study the CP violating effects in the decay. We show that to have CP violation in the decay, one has to consider both linear and circular photon polarizations. In the standard model, the polarizations are vanishingly small. However, model-independently, i.e. using only experimental constraint imposed by the limit on Br(η→π+π-) it can be up to O(10%). We also explore various possible operators and we find that the tensor type operator, possibly arising from a nonzero CP violating electric dipole moment of the strange quark, can induce a sizable linear photon polarization.