Fundamental symmetry tests with the francium laser trap facility at ISAC

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The fundamental forces of nature are one of the fascinating subjects that can be studied at ISAC, Canada's 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. We have established a francium trapping facility at ISAC; in collaboration with researchers from the United States and Mexico, we will then use this francium source to carry out a series precision experiments using laser and microwave spectroscopy. First we will measure what is known as the hyperfine anomaly in a string of francium isotopes, giving us insight into the distribution of the nuclear magnetic moment within the nucleus. Another goal is to study parity-violating nucleon-nucleon interactions in francium by observing the nuclear anapole moments in a chain of francium isotopes; to date, only measurements in two single isotopes of cesium and thallium have been performed, and more data is crucial for a better understanding of hadronic parity violation in nuclear matter. Ultimately, we want to search for `new' physics outside the - so far very successful - Standard Model of particle physics by measuring nuclear-spin independent atomic parity-violation in francium.