"Investigation of the E2 and E3 matrix elements in 200Hg using direct nuclear reactions"
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). The observation of a permanent EDM would represent a clear signal of CP violation from new physics beyond 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 comprises 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 Munich, 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 (βλ) were extracted through coupled-channel calculations with global optical-model potential (OMP) parameter sets. The total B(E3; 0+ 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 levels were identified, including 50 newly observed levels. Spin-parity assignments and spectroscopic factors were extracted through distorted-wave Born approximation calculations with global OMP sets. The results from these two experiments will be presented.
Dr. Robert Wickham, Chair
Dr. Carl Svensson, Advisor
Dr. Paul Garrett, Advisor
Dr. Alexandros Gezerlis
Dr. Ben Kay, External Examiner (Argonne National Lab Lemont, Illinois)