Theory of parity violation in compound nuclear states: One particle aspects

Abstract

In this work we formulate the reaction theory of parity violation in compound nuclear states using Feshbach s projection operator formalism. We derive in this framework a complete set of terms that contribute to the longitudinal asymmetry measured in experiments with polarized epithermal neutrons. We also discuss the parity violating spreading width resulting from this formalism. We then use the above formalism to derive expressions which hold in the case when the doorway state approximation is introduced. In applying the theory we limit ourselves in this work to the case when the parity violating (PV) potential and the strong interaction are one body. In this approximation, using as the doorway the giant spin-dipole resonance and employing well-known optical potentials and a time-reversal even, parity odd one-body interaction we calculate or estimate the terms we derived. Among others, we evaluate numerically a new "direct" term and the channel coupling term first derived by Lewenkopf and Weidenmiiller, this in addition to the evaluation of the main "compound" term. In our calculations we explicitly orthogonalize the continuum and bound wave functions. We find the effects of orthogonalization to be very important. Our conclusion is that the present one-body theory cannot explain the average longitudinal asymmetry found in the recent polarized neutron experiments. We also confirm the discrepancy, first pointed out by Auerbach and Bowman, that emerges, between the calculated average asymmetry and the parity violating spreading width, when distant doorways are used in the theory.PACS number(s): 24.80. Dc, 24.60.Dr, 25.40. Ny, 24.10.i

Spin measurements forSm147+nresonances: Further evidence for nonstatistical effects

“…However, all ten measured asymmetries for resonances below 250 eV had the same sign. Models proposed to explain this sign effect are based on either distant [38,39,40,41,42,43,44,45,46] or nearby [47,48,49,50,51,52,53] (parity) doorway states. Perhaps the same type of model could be invoked to explain the observed deviations in the neutron width distributions from the expected PT shape, while at the same time these deviations might provide some clue to the physical origins of the doorway.…”

Parity and Time Reversal Invariance Violation in Neutron-Nucleus Scattering

“…There are also other explanations of the permanent sign effect in 232 Th. The contributions from Distant doorway states [60,[73][74][75][76] appear to be too small. The neutron PV potential scattering contribution [70,109], as well the contributions calculated using optical potentials [71,110,111], also seem to be too small.…”

“…Several papers [60,[70][71][72][73][74][75][76] described in the review [9] suggested mixing of the doorway states of opposite parity as a source of the permanent sign effect in 233 Th. For example, in Refs.…”

Nearby Doorway States, Parity Doublets, and Parity Mixing in Compound Nuclear States

“…However, when the same size matrix element was used the average asymmetry was almost two orders of magnitude smaller than measured. Recently more extensive theoretical investigations characterized several terms that could contribute to PNC asymmetries in the CN [8,9]. Additional terms were derived and evaluated.…”

“…We will refer to these resonances as p 1/2 . The leading term of the asymmetry P can be written [6,9] P (E r ) = −2…”