Statistical theory of parity nonconservation in compound nuclei

Abstract

We present the first application of statistical spectroscopy to study the rootmean-square value of the parity nonconserving (PNC) interaction matrix element M determined experimentally by scattering longitudinally polarized neutrons from compound nuclei. Our effective PNC interaction consists of a standard two-body meson-exchange piece and a "doorway" term to account for 0 − spin-flip excitations. Strength functions are calculated using realistic single-particle energies and a residual strong interaction adjusted to fit the experimental density of states for the targets, 238 U for A ∼ 230 and 104,105,106,108 Pd for A ∼ 100. Using the standard Desplanques, Donoghue, and Holstein estimates of the weak PNC meson-nucleon coupling constants, we find that M is about a factor of 3 smaller than the experimental value for 238 U and about a factor of 1.7 smaller for Pd. The significance of this result for refining the empirical determination of the weak coupling constants is discussed.

Global properties of fp-shell interactions in many-nucleon systems

“…The theory of spectral distributions is an excellent approach for studying microscopic interactions [4,24,25] and continues to be a powerful concept with recent applications in quantum chaos, nuclear reactions and nuclear astrophysics including studies on nuclear level densities, transition strength densities, and parity/time-reversal violation (for example, see [26,27,28,29,30,31,32,33,34,35]). The significance of the method is related to the fact that low-order energy moments over a certain domain of single-particle states, such as the energy centroid of an interaction (its average expectation value) and the deviation from that average, yield valuable information about the interaction that is of fundamental importance [7,11,25,36,37,38,39,40,41] without the need for carrying out large-dimensional matrix diagonalization and with little to no limitations due to the dimensionality of the vector space.…”

Underlying symmetries of realistic interactions and the nuclear many-body problem

“…The theory of spectral distributions of French and collaborators is an alternative approach for studying effective interactions [8,15,16] and continues to be a powerful concept with recent applications in quantum chaos and nuclear astrophysics including studies on nuclear level densities, transition strength densities, and parity/timereversal violation (for example, see [17,18,19,20,21,22]). The significance of the method is related to the fact that low-order energy moments over a certain domain of single-particle states, such as the energy centroid of an interaction (its average expectation value) and the deviation from that average, yield valuable information about the interaction that is of fundamental importance [11,16,23,24,25,26,27,28,29] without the need for carrying out large-dimensional matrix diagonalization and with little to no limitations due to the dimensionality of the vector space.…”

Measurement of parity-violatingγ-ray asymmetry in the capture of polarized cold neutrons on protons

“…The weak NN interaction is also one of the few systems thought to be sensitive to quark-quark neutral current effects at low energy since charged currents are suppressed in ∆I = 1 NN processes by V 2 us /V 2 ud ≃ 0.1. Quark-quark and NN weak interactions also induce parity-odd effects in electron scattering [7][8][9][10], nuclear decays [11], compound nuclear resonances [12,13], and atomic structure, where they are the microscopic source for nuclear anapole moments [14][15][16][17]. The comparison between NN weak amplitudes in few nucleon systems and heavy nuclei can also offer theoretical insight into the relative importance of possible heavy Majorana particle exchange in neutrinoless double beta decay [18].…”