Electric Dipole Moment
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Measurement of permanent dipole moments in storage ringsCopyright: © Jörg Pretz
The Standard Model of particle physics can not explain the reason for our existence, because it is not able to describe the obvious existing matter-antimatter asymmetry of the universe sufficiently. Physics beyond the standard model is required and is searched for.
An example of this are measurements at the highest energies (eg at the LHC). Complementing this are precision measurements at lower energies, as they are required in searches for permanent electric dipole moments (EDMs).
A particle has a permanent electric dipole moment, when the center of mass of the positive and negative charge distributions are different. Permanent EDMs of particles violate both time- (T) and parity invariance (P) and are also CP-violating due to the CPT theorem. The discovery of such, beyond the Standard Model CP violation, would be an important milestone in the search for the causes of the matter-antimatter asymmetry in the universe.
Measuring the neutron-EDM (nEDM) are carried out in many laboratories worldwide. So far there are no direct measurements of EDMs of charged particles. These high precision experiments on novel storage rings are required. The experimental approach to perform these tests is based on the precession of the particle spins due to its EDMs in electromagnetic fields. The structure (or the absence) of a vertical polarization component as a function of storage time would be an indication of a finite EDM (or provided at least one upper limit). Such measurements with polarized particle beams are to be performed at the cooler synchrotron COSY at first and then to a dedicated storage ring in Jülich.