Spin tune response to vertical orbit correction at COSY

Searches of electric dipole moments (EDM) of charged particles in pure magnetic rings, such as COSY, or electrostatic and hybrid magnetic-electric storage rings, planned in the future, require new methods to disentangle the EDM signal from the large background produced by magnetic dipole moments. In these experiments, the sources of systematic background are in-plane magnetic fields. It is important to distinguish the origins of the in-plane magnetic fields, which could be produced intentionally by vertical orbit correction to keep the beam on a closed path, or unintentionally due to the alignment errors of the magnets. We propose to use the method of spin tune mapping to determine the relative importance of those two origins. At the first stage, the model of COSY should be verified for the spin tune shifts when vertical three-steerer closed-orbit bumps are applied. At the second stage, the spin tune response to vertical orbit correction in the arcs will testify its contribution to the systematic background. (author)