May 2021
Tactically clever: a test lab for new physics
“We have a common goal: we want to use the isotope thorium-229 to test the standard model of particle physics. To this end, we are working hand in hand with our colleagues from experimental atomic physics in the TACTICa project. The name TACTICa (Trapped And Cooled Thorium Ion spectroscopy via Calcium) says it all: we trap individual thorium-229 ions in a special ion trap in order to examine them using laser spectroscopy. To do this, we first have to slow down the thorium ions – or cool them, as we say. Calcium, which is also on board, helps us with this. We call this method quantum logic spectroscopy: we actually want to find out something about the thorium, but in order to manipulate it we need calcium as a helper, as a logic ion.
©: Angelika Stehle
What makes thorium-229 so special? With the metastable state thorium-229m, it has by far the lowest excited energy level of all currently known 3,800 atomic nuclei. It is therefore the only nuclear transition that can potentially be acquired with lasers. The extremely precise measurement of this transition and the two nuclear states opens up exciting perspectives. In particular, thorium will become a test lab for new physics for us. For example, we want to answer the question of whether certain natural constants are perhaps not constant at all, but change with time or location. This in turn is predicted by some theories on Dark Matter that go beyond the standard model.
We are currently working in nuclear chemistry on producing suitable uranium-233 sources and guiding the thorium-229 daughters from the radioactive decay of uranium into our trap – while on the theoretical side we are developing models for what the smallest deviations between measured and expected results can reveal about new physics. We have already been able to show that the method works in principle.”
Dr. Raphael Haas is a nuclear chemist in the group of Professor Christoph Düllmann, Anna Viatkina studied in Russia and is working on her PhD thesis as a theoretical physicist in the group of Professor Dmitry Budker. The TACTICa project is funded as part of a “Helmholtz Network of Excellence” in the field of “Matter and the Universe”.