Investigation of the E2 and E3 matrix elements in 200Hg using direct nuclear reactions




Rand, Evan Thomas

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University of Guelph


A nuclear-structure campaign has been initiated to investigate the isotopes of Hg around mass 199. To date, 199Hg provides the most stringent limit on an atomic electric dipole moment (EDM). Standard Model predictions of the EDM in 199Hg are many orders of magnitude below current experimental reach. There are, however, many models beyond the Standard Model, such as multiple-Higgs theories and supersymmetry, that generally predict much larger EDMs within experimental reach. The observation of a large permanent EDM would represent a clear signal of CP violation from new physics outside the Standard Model. Theoretical nuclear-structure calculations for 199Hg are challenging, and give varied predictions for the excited-state spectrum. Understanding the E2 and E3 strengths in 199Hg will make it possible to develop a nuclear-structure model for the Schiff strength based on these matrix elements, and thereby constrain present models that predict the contribution of octupole collectivity to the Schiff moment of the nucleus. One of the most direct ways of measuring the matrix elements connecting the ground state to excited states is through inelastic hadron scattering. The high level density of a heavy odd-A nucleus like 199Hg makes a measurement extremely challenging. Complementary information can, however, be determined for states in the neighbouring even-even isotopes of 198Hg and 200Hg, and single-nucleon transfer reactions on targets of even-even isotopes of Hg can yield important information on the single-particle nature of 199Hg. The work presented here is the result of two experiments which used a 22-MeV deuteron beam incident on an isotopically enriched target of 200Hg32S. These experiments were performed using the Q3D magnetic spectrograph at the Maier-Leibnitz Laboratory, in Garching, Germany. The first experiment was an inelastic deuteron scattering experiment, 200Hg(d,d’)200Hg, populating 97 states up to an excitation energy of 4.2 MeV. Fifty-four states were newly discovered. Deformation parameters were extracted through coupled-channel calculations with global optical-model potential (OMP) parameter sets. The total B(E3; 0+ to 3-) strength in this region was estimated to be 0.55+0.12-0.18 e2b3, where the reported errors represent the upper and lower limits. The second experiment was a single-nucleon transfer reaction into 199Hg, 200Hg(d,t)199Hg, up to an excitation energy of 3 MeV. In total, 91 excited levels were identified, including fifty newly observed levels in this work. Spin-parity assignments and spectroscopic factors were extracted through distorted-wave Born approximation calculations with global OMP sets. The results from these two experiments are presented and further discussed in this thesis.



direct nuclear reactions, deuteron inelastic scattering, (d,t) pickup reaction, 199Hg, 200Hg, electric dipole moment, Schiff moment, DWBA, Coupled-channel calculations