Constraints on a Parity-Conserving/Time-Reversal-Non-Conserving Interaction

TL;DR

This paper reviews experimental constraints on parity-conserving and time-reversal-non-conserving interactions, emphasizing the limits from neutron electric dipole moment measurements and nucleon scattering experiments, and discusses the implications for fundamental symmetries.

Contribution

It provides a comprehensive analysis of experimental limits on P-even/T-odd interactions, highlighting the most sensitive measurements and theoretical implications.

Findings

Neutron electric dipole moment limits constrain P-odd/T-odd interactions.

Charge-symmetry breaking in neutron-proton scattering sets bounds on P-even/T-odd interactions.

Other experimental methods are less sensitive by at least an order of magnitude.

Abstract

Time-Reversal-Invariance non-conservation has now been unequivocally demonstrated in a direct measurement at CPLEAR. What about tests of time-reversal-invariance in systems other than the kaon system? Tests of time-reversal-invariance belong to two classes: searches for parity violating (P-odd)/time-reversal-invariance-odd (T-odd) interactions, and for P-even/T-odd interactions (assuming CPT conservation this implies C-conjugation non-conservation). Limits on a P-odd/T-odd interaction follow from measurements of the electric dipole moment of the neutron (with a present upper limit of 6 x 10^-26 e.cm [95% C.L.]). It provides a limit on a P-odd/T-odd pion-nucleon coupling constant which is less than 10^-4 times the weak interaction strength. Experimental limits on a P-even/T-odd interaction are much less stringent. Following the standard approach of describing the nucleon-nucleon interaction in terms of meson exchanges, it can be shown that only charged rho-meson exchange and A_1 meson exchange can lead to a P-even/T-odd interaction. The better constraints stem from measurements of the electric dipole moment of the neutron and from measurements of charge-symmetry breaking in neutron-proton elastic scattering. The latter experiments were executed at TRIUMF (497 and 347 MeV) and at IUCF (183 MeV). Weak decay experiments may provide limits which will possibly be comparable. All other experiments, like gamma decay experiments, detailed balance experiments, polarization - analyzing power difference determinations, and five-fold correlation experiments with polarized incident nucleons and aligned nuclear targets, have been shown to be at least an order of magnitude less sensitive.