Precision spectroscopy of neutral radium: towards searches for permanent electric dipole moments

PhD ceremony: Mr. B. Santra, 11.00 uur, Academiegebouw, Broerstraat 5, Groningen

Dissertation: Precision spectroscopy of neutral radium: towards searches for permanent electric dipole moments

Promotor(s): prof. K. Jungmann

Faculty: Mathematics and Natural Sciences

Searches for non-zero permanent Electric Dipole Moments (EDM) of fundamental particles provide one promising approach for testing the range of validity of fundamental symmetries. An EDM can arise from the known CP-violation within the Standard Model (SM). However it is lower by several order of magnitude compared to the sensitivity of current and proposed EDM searches. In order to push the EDM limit towards the SM prediction and beyond we have to explore the sensitivity of experiments which depends on various issues.

This thesis describes a new experimental approach to search for an EDM in radium which provides the highest possible sensitivity in such systems. The sensitivity depend on the particular isotope and the atomic state considered. Production of rare isotopes of radium with 1/2 nuclear spin and study the atomic physics properties such as, absolute frequency measurement of the strongest laser cooling transition and most suitable transition for trapping the radium atoms are the main challenges of this thesis work. The challenge is accomplished by successful operation of effusive atomic beam of the isotope ²²⁵Ra, production of thermal ²¹³Ra atoms and absolute frequency measurement of the main cooling transition 7s^{2 1}S₀ - 7s7p ¹P₁ and trapping transition 7s^{2 1}S₀ - 7s7p ³P₁ with an accuracy better than 5 MHz. The hyperfine structure interval of the 7s7p ¹P₁ level is also determined with an accuracy better than 4 MHz which is in good agreement with previous measurement at the ISOLDE facility at CERN. Further, a strategy based on two-photon Raman transition is demonstrated with barium atoms for sensitive probing of the metastable D stated in radium. These measurements provide indispensable input to investigate SM predictions and beyond by means of observing an EDM in optically trapped radium atoms.