A Limit on Nuclear T-violation Prom the Neutron Electric Dipole Moment?

Time reversal non-invariance in nuclei has recently been parametrized in terms of a four point coupling, of undetermined strength, of an isovector photon, a charged pion and the nucleon current. If parity violation is introduced via the weak interaction, this coupling is restricted, by the failure to observe a neutron electric dipole moment, to a size which is an order of magnitude smaller than the limit imposed by present nuclear y-decay experiments . (Submitted to Phys. Rev. Comments and Addenda. ) t Work supported in part by the U. S. Atomic Energy Commission. * Harkness fellow 19’71-1973. In a recent letter’ Clement and Heller discuss the expected size of T-violating effects in nuclear Y-decay arising from a possible C and T non-invariance of the electromagnetic interaction. 2 We investigate here the limit imposed on these effects by the failure to observe a neutron electric dipole moment. 3 Clement and Heller calculate the T-odd two nucleon matrix elements of the long range El and Ml multipole operators from a supposed T-violation in the four point coupling of an isovector photon, a charged pion and the nucleon current. They make a ‘rough guess’ as to that size of coupling constant which would correspond to a large or ‘maximal’ effect and conclude that the most sensitive present limit on the EZ-Ml phase (in 36 Cl) still falls short of probing such an effect. The virtue of this approach is that it avoids the consideration of offshell nucleons that necessarily attends any attempt to parametrize T-violation without P-violation at the NNy vertex. 4 The question arises whether the coupling they take as ‘maximal’ would lead to observable effects in other low energy T-violation tests. More usefully, we would like to know whether the present nuclear experiments, when interpreted in their model, are more or less sensitive to electromagnetic T-violation than is the present experimental upper limit3 of 5 x 10 -23 cm on the neutron electric dipole moment (EDM). Cur calculation indicates that they are an order of magnitude less sensitive. Consider the following conventional, P-violating, and T-violating Lagrangians : 9 = GG. 7 y51y, (1) Lq = gp (7 cG3 w, (2) g2 = ig,(e/mP)~(++x ?), ~~$1 ‘a Fpv , (3)