Towards atomic parity violation in francium : spectroscopy of highly forbidden transitions in rubidium

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The fundamental forces of nature are one of the fascinating subjects that can be studied at ISAC, Canada's new world-class radioactive beam facility at TRIUMF. In particular, the weak force, causing the beta-decay of nuclei, is unique in exhibiting the phenomenon of parity-violation: the mirror images of physical processes mediated by the weak force are not observed in nature. ISAC offers a unique possibility to study atomic parity-violation in francium (Fr), an element combining a very heavy nucleus (Z=87) with the simple, essentially hydrogenlike, valence structure of an alkali. Fr nuclei are the least stable among the first 103 elements in the periodic table, the longest-lived isotope decays in only 23 minutes. To make optimum use of the minute sample, the Fr atoms will be slowed down with laser light and captured into a `magneto-optical' laser trap, suspended in free space at temperatures millions of times colder than room temperature. Precise laser spectroscopy will allow us to observe the effects of parity-violation. The ultimate goal will be to search for `new' physics outside the - so far very successful - Standard Model of particle physics. The great technical challenge of this experiment is to implement robust and extremely efficient atom-manipulation and signal-detection methods to make optimum use of the minute Fr sample. A precursor experiment with stable rubidium atoms at the University of Manitoba will develop the required techniques and look for the effects of 'negative-energy states'.