Nuclear Matrix Elements for Tests of Fundamental Symmetries

The nuclear matrix elements for the momentum quadrupole operator and nucleon spin operator are important for interpretation of precision atomic physics experiments that search for violations of Lorentz and CPT symmetry and for new spin-dependent forces. We use the configuration-interaction nuclear shell model and self-consistent mean field theory to calculate the relevant matrix elements in $^{21}$Ne, $^{131}$Xe, and $^{201}$Hg. We find that the spin expectation values in these nuclei are dominated by the odd neutron, while the quadrupole moment of the nucleon momentum, M, has comparable neutron and proton contributions. These are the first microscopic calculations of the nuclear matrix elements for the momentum quadrupole tensor that go beyond the single-particle estimate. We show that they are strongly suppressed by the many-body correlations, in contrast to the well known enhancement of the spatial quadrupole nuclear matrix elements.