Electric Dipole Moments
Electric dipole moments (EDMs) arise when in a system positive and negative charges are separated. In everyday life, a battery has an electric dipole moment. Also the water molecule has an EDM, which is responsible for the attraction between the molecules. The EDM is also a fundamental property of a subatomic particle, such as mass, charge, spin, or magnetic magnetic moment. However, so far no EDM has been found for a subatomic particle. This has good reasons. In contrast to more complex objects like molecules for subatomic particles like electron, proton, neutron or deuteron, under very general conditions, EDMs only arise when a combined violation versus charge exchange C and parity transformation P, called CP-violation is present. CP-violation is one important ingredient of the standard model of particle physics, but its far too small to generate measurable EDMs. Why should one nevertheless continue to search for it?
This is related to one of the biggest unsolved mysteries in cosmology and particle physics: The disappearance of antimatter from an initial equilibrium of matter and antimatter in the early universe. The interactions known to us in the standard model, especially the above mentioned CP-violation, which distinguishes between matter and antimatter, are not sufficient to solve this puzzle. Extensions of the standard model predict further CP-violating interactions which also lead to detectable EDMs. Thus, if one finds an EDM, one would have hints for the observed dominance of matter in the universe as well as physics beyond the Standard Model!
Up to now most of the EDM measurements were mostly done with neutral particles. With new techniques it is now possible to perform dedicated EDM experiments with charged hadrons at storage rings. The experimental program also includes the search for dark matter particle candidates (axion like particle) which will result in an oscillating electric dipole moments.
Within the JEDI collaboration we are performing experiments at the Cooler Synchrotron COSY. COSY with its possibility to provide and accelerate polarized protons and deuterons offers unique possibilities in the world to perform such experiments. Within a larger community of the CPEDM collaboration, we are investigating the design of a dedicated storage ring for charged hadron EDM measurements.
Prof. Jörg Pretz
Building 07.1 / Room 354