Problems and advantages of measuring parity and time-reversal invariance in nuclei

Abstract

In the low energy regime parity violation for pure hadronic systems can be expressed essentially by six effective weak meson-nucleon coupling constants, three of which are only known at present. Additional independent experiments have been proposed involving light, heavy and compound nuclei, to determine all six coupling constants unambiguously. Though heavy nuclei offer enhancement factors of up to (10 5), the difficulty to extract relevant weak meson-nucleon coupling constants from experiments involving heavy nuclei increases substantially. In this context the statistical model of compound nuclei provides an additional option for the extraction of these coupling constants. In contrast to parity violation (PV) tests, time-reversal in variance (TRI) information that is extracted from 2-body reactions, results from a comparison of two different observables. As a consequence, the accuracy of these experiments is reduced. In view of the mechanisms that enhance PV, TRI tests have been performed that utilize heavy nuclei too. At COSY a novel, true T-odd, P-even null-experiment has been proposed that has the potential to test TRI to an accuracy of 10 −6 in p - d -scattering. For this test the COSY ring serves as accelerator, ideal forward spectrometer and detector.