The early Universe contained the same amount of matter and anti-matter and, if the Universe had behaved symmetrically as it developed, every particle would have been annihilated by one of its antiparticles, leaving behind no matter but only photons.
One of the great mysteries in the natural sciences is therefore why there is matter at all present in our world rather than only light, and why matter dominates over anti-matter in the visible Universe. The reason for this apparent inequality must be sought in a difference between matter and anti-matter, related to the breaking of a fundamental symmetry called charge-parity (CP)-violation (CPV).
In the Standard Model of elementary particle physics (SM), CPV is observed, but its size (due to the electroweak interaction with essentially no contribution from the strong interaction) is greatly insufficient to explain the matter anti-matter asymmetry and further sources of CPV must be sought. These could manifest themselves in electric dipole moments (EDMs) of elementary particles, which occur when the centroids of positive and negative charges are mutually and permanently displaced. An EDM observation would also be an indication for physics beyond the SM.
EDMs are searched for in different systems (neutrons (n), atoms, molecules and even bulk material), but, up to now, no EDM has been observed - only ever smaller upper limits have been deduced, including indirekt results for the proton (p) and the electron (e). A new line of EDM-search has recently been suggested for charged particles (protons and deuterons (d), and 3-helium) in storage rings, aiming at direct limits with unprecedented sensitivity. Once EDMs have been discovered - results for different particles (e, n, p, d) are required to pin down the CPV sources.
The srEDM-project will lay the foundations for direct EDM searches of charged hadrons in a completely new class of precision storage rings by developing the required key technologies. It will exploit the existing conventional storage ring COSY (based on magnetic-field deflection) of Forschungszentrum Jülich (Germany) and it will also provide a first measured EDM limit for deuterons.
The EDM measurement principle, the time development of the polarization vector (which is oriented along the EDM) subject to a perpendicular electric field, is simple, but the smallness of the EDM together with the potentially overwhelming impact of magnetic dipole moment (MDM) effects make this an enormously challenging project. A staged approach is required – from R&D for key-technologies towards a dual-beam all-electric precision storage ring with simultaneously circulating clock-wise and counter clock-wise beam bunches, running in the so called "frozen spin" condition – to achieve the highest EDM sensitivity.
The srEDM project has an outstanding science case with the potential to solve "the puzzle of our existence" (the baryon asymmetry of our Universe) and the search for axion/axion-like particles (candidates for Dark Matter in our Universe). By overcoming the technological and metrological challenges, it will also provide many new advances in accelerator and detector technology.
