Search for the Charged Particle Electric Dipole Moments in Storage Rings

The idea of searching for the electric dipole moment (EDM) of proton and deuteron using polarized beams in a storage ring was originally proposed at Brookhaven National Laboratory (BNL), USA. Currently, the Jülich Electric Dipole moment Investigations (JEDI) collaboration develops the conceptual design of such a ring specifically for the search of the deuteron electrical dipole moment (dEDM). The idea is that the oscillation of the spin due to a possible finite electric dipole moment is separated from the influence of the magnetic dipole moment (MDM), and the spin behavior indicates the existence of dEDM. In connection with this problem, two questions arise: (i) how to create conditions for maximum growth of the total EDM signal of all particles in the beam bunch, and (ii) how to differentiate the EDM signal from the induced MDM signal. For the design of such a ring, we need to address three major challenges: - the ring lattice should meet the conditions of beam stability, and it has to have incorporated straight sections to accommodate the accelerating station, equipment for injection and extraction of the beam, a polarimeter, and sextupoles; - the polarization lifetime of the beam must be around ~1000 seconds; - systematic errors have to be minimized to eliminate the induced fake EDM signal. In my contribution, I will present the current status of the project

Search for the Optimal Spin Decoherence Effect in a QFS Lattice

Measurement of electric dipole moment (EDM) in a storage ring requires the spin decoherence in a particle bunch to be less than 1 rad in 1000 s, which corresponds to about 1 billion turns. The quasi-frozen spin (QFS) method* has been proposed for deuteron EDM search. In a QFS lattice, spin direction turn in magnetic bend sections is compensated by spin direction turn in electrostatic bend sections, and thus the spin direction at a point in the lattice is approximately constant. We consider a QFS lattice with an RF cavity and seven families of sextupoles. In COSY Infinity, calculations were done using transfer maps of the 7th order, with symplectic tracking using the Extended Poincaré (EXPO) generating function and the most accurate COSY Infinity fringe field mode. We have optimized the sextupole strengths to minimize the spin decoherence. Using these sextupole strengths, we have done spin tracking of the lattice and analyzed the growth of spin decoherence as a function of the number of turns. Within their scope, our results indicate the feasibility of the QFS method

Spin Tune Decoherence Effects in Electro- and Magnetostatic Structures

In Electric Dipole Moment search experiments with polarized beams the coherence of spin oscillations of particles has a crucial role. The decoherent effects arise due to spin tune dependence on particle energy and particle trajectory in focusing-deflecting fields. They are described through the n-th order spin tune aberrations. Since the first order is suppressed by RF field, the second order plays crucial role. It depends on the orbit lengthening and on the odd order field components. We consider the spin decoherence effects and methods of their compensation in different channels, electrostatic, magnetostatic linking the decoherence effects with common characteristics such as the momentum compaction factor, the chromaticity and others

Investigation of Lattice for Deuteron EDM Ring

The quasi-frozen spin (QFS) concept of a storage ring for deuteron EDM measurement is based on the fact that the anomalous magnetic moment has a small negative value. Due to this fact, the rotation of spin in two parts of ring with the magnetic and electric fields relative to the momentum can compensate each other. In contrast to the concept of frozen spin we have the freedom to choose the ring parameters and also greatly simplified lattice. We consider two possible options for the lattice based on QFS concept and compare them with the frozen spin lattice proposed by BNL. In the first QFS option, we use completely separate electric and magnetic parts that form a structure. In the second option, we suggest using only two magnetic arcs with two straight sections having the straight elements with magnetic and electric fields. The straight elements have a horizontal electric field of 120 kV/cm and a vertical magnetic field of 80 mT. They provide the compensation for the spin rotation in the arc and at the same time allow having straight electric plates without the higher orders field. This scheme could be tested in the COSY ring at FZ Jülich to prove the quasi-frozen spin concept