Chiral Anomaly Tests

Abstract

For the gamma-pion interaction, the perturbative expansion of the effective chiral Lagrangian (chi-PT) can be limited to terms quartic in momenta and masses (O(p4)), or to higher order. The abnormal intrinsic parity (chiral anomaly) component of the lagrangian leads to interesting predictions for the processes pi0 -----> 2 gamma and gamma ----->3 pi. These are described by the amplitudes F_{pi} and F_{3pi}, respectively. We demonstrate that the O(p4) value of F_{3pi} disagrees with existing data, while the O(p6) value is nearly consistent. We describe how Fermilab experiment E781 can get improved data for tests of the chiral anomaly.