Precision experiments with stored ions and antimatterMax Planck Institute for Nuclear PhysicsUniversity of HeidelbergEuropean Research Council
Precision experiments with stored ions and antimatter
 
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Dr. Alban Kellerbauer
a.kellerbauer@mpi-hd.mpg.de

Tel: +49 6221 516 138
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Max Planck Institute for Nuclear Physics
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High-resolution spectroscopy on the osmium anion

Experimental results from ATHENA, confirmed by independent measurements performed with the ATRAP experiment, have shown that the produced antihydrogen is several orders of magnitude hotter than expected, presumably because recombination sets in before the antiprotons have thermalized with the positrons. An alternative production technique demonstrated by ATRAP, which uses resonant Rydberg charge exchange, shows promise in this regard, but can at best reach the temperature of the surrounding trap. Since the trapping of antihydrogen for precision tests of matter-antimatter symmetry critically depends on the antihydrogen temperature, novel approaches for the production of ultra-cold antihydrogen are required.

For this purpose, we have proposed a technique based on the pre-cooling of antiprotons by indirect laser cooling, which should ultimately allow the production of antihydrogen at temperatures well below 1 mK, and thus even below the Doppler cooling limit of direct laser cooling with Lyman-alpha radiation. The scheme is based on the laser cooling of a cloud of negative ions, which in turn sympathetically cool a smaller number of antiprotons. Due to the large ratio of the masses of the antiproton and the electron, antihydrogen will then be formed essentially at the antiprotons' temperature.
Up until a few years ago, there were no known negative ions that had bound excited states with opposite parity from the ground state (required for a strong electric-dipole transition), but such a configuration has recently been discovered in the negative osmium ion, thus making the proposed technique feasible.

Since July 2006, preparatory investigations on the negative osmium ion have been funded by an Emmy Noether Grant of the German DFG funding agency. Recently, the first milestone of the project was achieved when we studied the bound–bound transition in 192Os− by high-resolution collinear spectroscopy. In addition to the transition frequency, the cross-section was also measured to high precision. These results pave the way for the next goals of the experiment: Spectroscopy in an external magnetic field, and actual laser cooling of Os−.

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