Special Seminars 2009

Abstract

Abstract

Nuclei with an extreme unbalanced ratio of protons-to-neurons are referred to as exotic. The most exotic ones ever found on Earth are the halo nuclei of helium and lithum with a three time more neutrons than protons. Teetering on the edge of nuclear stability, the properties of these exotic halo nuclei have long been recognized as one of the most stringent tests of our understanding of the strong force. Only recently has it become possible to carry out precision mass measurement of the halos, such as 11Li, using a Penning trap spectrometer. Measurements were carried out at the TITAN (Triumf's Ion Trap for Atomic and Nuclear science) facility at TRIUMF where a trap system is coupled to the ISOL-based rare beam facility ISAC. Penning traps are proven to be the most precise device to make mass measurements, but were until now not able to reach these atoms, due to limitations in production yield and short half-lives. At TRIUMF we managed, and in addition to its unprecedented accuracy, dm/m = 6x10-8, the measurement of 11Li is remarkable for the fact that with a half-life of only 8.8 ms, it is the shortest-lived nuclide ever to be weighed with this technique. Furthermore, new and improved masses for 6,8He, and 11,12Be, hence precision mass measurements on 1,2, and 4-neutron halos have been performed. Using theses precision masses, other properties, such as charge radii form laser spectroscopy, can be derived. This allows one to test and refine state-of-the-art nuclear theory,and shows that three-body forces need to be considered when describing these nuclei. An overview of the TITAN mass measurement program and its impact in understanding halo nuclei will be given. TRIUMF has plans and received some funding to extent the rare-beam program using additional proton and electron drivers. Plans and status are discussed.

Abstract

Abstract

Experimental searches for permanent electric dipole moments (EDMs) provide extremely sensitive probes for new sources of CP-violation. While standard model EDM predictions are many orders of magnitude smaller than current experimental sensitivity, many theoretical extensions such as Supersymmetry generate EDMs well within reach of existing experiments. The three main classes of EDM searches are: measurements on bare neutrons; measurements on paramagnetic atoms or molecules, mainly sensitive to the electron EDM; and measurements on diamagnetic atoms, mainly sensitive to CP-violating interactions between nucleons. The most sensitive diamagnetic experiment is performed on Hg-199 atoms at the University of Washington in Seattle. A new measurement of the Hg EDM was recently completed resulting in an upper bound |d(Hg)| <= 3.1 x 10^-29 e cm, a factor of seven improvement on the previous limit. Details on the experimental technique and results will be given, along with theoretical implications of the new limit, and prospects for improvement.