Revealing Antimatter’s Origins
In science fiction stories, it is either the inexhaustible energy source of the future or a superweapon of galactic magnitude: antimatter. In fact, antimatter can
 |
neither be found on Earth nor in space, is extremely complex to produce and, thus, difficult to study. Therefore, in order to track down the origin of matter and antimatter in the universe, researchers are measuring the power of the electrical dipole moment of ultra cold neutrons, which represents a measure for the different physical properties of matter and antimatter.
Neutrons are electrically neutral particles when observed externally. As the neutron contains both positively and negatively charged quarks, it would be conceivable that there exist equally large positive and negative charges at a minimal spatial distance from one another in its interior. The neutron would then be an electrical dipole with two oppositely charged poles.
The electrical dipole moment of the neutron is namely a measure of how strongly matter and antimatter differ from one another in their physical properties. At the Institut Laue-Langevin (ILL) in Grenoble, a research group is attempting to measure the magnitude of the electrical dipole moment of neutrons (nEDM) with high accuracy. In these experiments, the behavior of extremely slow ultra cold neutrons (UCN), is investigated in magnetic and electrical fields.
Due to the fact that neutrons possess a spin and, thus, have a magnetic moment, they also are subject to electromagnetic interaction. If an additional electrical field is applied, the neutron, if it possesses an electrical dipole moment, would have to slightly change its properties in a magnetic field. So far, experiments have shown no sign that would indicate an appreciable electrical dipole moment. However, due to its fundamental physical significance, reearchers are interested in further restricting the magnitude of the possible electrical dipole moment.
The prerequisite for further, yet more accurate measurements is a perfect insulation against electrical and magnetic radiation from the environment. Therefore, in order to significantly improve the measurement uncertainty, a new set-up of the experiment with a stronger UCN source and better magnetic shielding is planned at at the Paul Scherrer Institut (PSI). Magnetically soft mumetal is a material that already has been used in a new type of shielding designed, set-up and tested by researchers at the Physikalisch-Technische Bundesanstalt, creating what is currently the best-shielded magnetic cabin in the world. The valuable know-how that was collected at the PTB during the cabin’s assembly will be used for the construction, testing and assembly of the new shielding for the neutron experiment. The measuring systems available at PTB will be used for the preliminary investigation of facility components. Of particular importance is PTB’s expertise in detecting even the slightest magnetic impurities.
