1. Highlights from COSY (JEDI project)
August 29, | Andreas Lehrach
Forschungszentrum Jülich (IKP-4) & RWTH Aachen University (Ex.Physik IIIb)
on behalf of the JEDI collaboration
(Jülich Electric Dipole Moment Investigations)

2. Outline Introduction Motivation for EDM measurements
Principle and methods
Achievements
Spin coherence time investigation
Spin tune measurement
Preparation for spin tune feedback
Preparation for improved closed-orbit correction
Technical developments
RF Wien filter
Electrostatic deflector
Polarimetry
Beam position monitor

3. Electric Dipole Moments
Permanent EDMs violate parity P and time reversal symmetry T
Assuming CPT to hold,
combined symmetry CP violated as well.
EDMs are candidates to solve mystery
of matter-antimatter asymmetry

4. EDMs – Ongoing / planned Searches
@CAPP/IBS
P. Harris, K. Kirch … A huge worldwide effort

5. Limits for Electric Dipole Moments
EDM searches - only upper limits up to now (in ecm):
Particle/Atom
Current EDM Limit
Future Goal
Neutron
 3 10-26
10-28
199Hg
 3.1 10-29
10-29
129Xe
 6 10-27
10-30 – 10-33
Proton
 7.9 10-25
Deuteron ?
CP can have different sources
It is important not only to measure neutron,
but also proton, deuteron and light nuclei EDMs
in order to disentangle various sources of CP violation
Kern EDMs können viel größer sein(thoeretische Vorhersage) 5 5

6. Storage Ring EDM Project
… measure for development of vertical polarization 
EDM
Challenges:
Huge E-fields
Shielding B-fields
Spin coherence
Beam position
Polarimetry
(...)
JEDI
Jülich Electric Dipole Moment Investigations
~ 136 members
(11 countries and 37 institutes)

7. Spin Precession with EDM
Equation for spin motion of relativistic particles in storage rings
for
The spin precession relative to the momentum direction is given by:
Thomas-BMT equation plus extension for EDM
Magnetic Dipole Moment
Electric Dipole Moment

8. Frozen-Spin Method for Storage Ring EDM Searches
Approach: EDM search in time development of spin in a storage ring: B
“Freeze“ horizontal spin precession; watch
for development of a vertical component !
A magic storage ring for protons (electrostatic), deuterons, and helium-3
particle
p (GeV/c)
E (MV/m)
B (T)
proton
0.701
16.789
0.000
deuteron
1.000
-3.983
0.160
3He
1.285
17.158
-0.051
One machine with r ~ 30 m 8 8

9. Cooler Synchrotron COSY Dedicated EDM Storage Ring
Stepwise Approach
Measurements of charged particle EDMs from COSY to a dedicated EDM storage ring
Cooler Synchrotron COSY
Dedicated EDM Storage Ring
R&D at COSY
Precursor experiment for first direct measurement
Injector for dedicated EDM ring
CW-CCW beams
Dedicated ring with high-precision beam diagnostics and polarimetry

10. Cooler Synchrotron COSY
Experimental Setup for R&D at COSY
polarimeter
Inject and accelerate vertically polarized deuterons
Spin rotated with RF fields into horizontal plane
Move beam slowly (in 100 s) on internal target
Measure asymmetry and determine spin precession
precession
At 970 MeV/c deuterons: γG ·frev ≈ 120 kHz
turn spin
RF ExB Wien filter
Electron Cooler
RF Solenoid
Cooler Synchrotron
COSY
Polarized protons, deuterons
300/600 MeV/c GeV/c
Precision Polarimeter
Sextupole Magnets
Polarized proton and deuteron source
Ideal starting point to investigate
EDM measurements in storage rings

11. Measurement of Spin Coherence Time
109 polarized deuterons at 970 MeV/c, bunched and electron cooled adjust three arc sextupoles to increase spin coherence time
 Longest SCT for beam chromaticities close to zero at regular betatron tunes (Qx,y = 3.5 – 3.6)

12. Record In-Plane Polarization Lifetime
Using a Gaussian width definition, the lifetime is 782 ±117 s. The exponential width 2280 ± 336 s. This is a new record for in-plane polarization lifetime, exceeding the Novosibirsk results for electrons by about three orders of magnitude.
Phys. Rev. Lett. 117, (2016).

13. EDDA Detector to measure asymmetries
Spin Tune Measurement at COSY
EDDA Detector to measure asymmetries
Sophisticated read-out system, which can time stamp individual event arrival times with respect to turn number:
Map events into first spin oscillation period
Analyse the spin phase advance throughout the cycle
Phys. Rev. STAB 17 (2014)
Phys. Rev. Lett. 115 (2015)

14. Stability on a Turn-by-Turn Basis
Study long term stability of an accelerator
Develop feedback systems to minimize variations
Phase-locking the spin precession to RF devices possible

15. In-plane polarization
Resonance Method in Magnetic Rings
RF ExB dipole in “Wien filter” mode
 Avoids coherent betatron oscillations
Modulation of horizontal spin precession in the RF Wien filter
EDM’s interaction with the motional electric field in the rest of the ring
continuous buildup of vertical polarization in a horizontally polarized beam.
net effect due to EDM
Investigation of sensitivity and systematic limitations
In-plane polarization

16. Spin-tune Based Feedback System
Left/right asymmetry as a measure of the vertical polarization. At t=85 s the spins are rotated into the horizontal plane, at t=115 s the solenoid is turned back on. The absolute values for the build-up for the two states are different as the initial polarization differs.
Initial slope of the polarization build-up as function of the relative phase (online result). The difference in amplitude is due to the different degrees of polarization of the two initial states.
Courtesy: V. Hejny

17. Systematic Limitations for EDM Measurements at COSY
Absolute average change of the vertical spin component ΔSy per turn for different ΔyRMS and an initial Wien filter phase 0°. Utilized Wien filter magnetic field: 10-4 mT and corresponding electric field with a length of 0.8 m. Different ΔyRMS generated by randomized vertical quadrupole shifts assuming Gaussian distributed misalignment errors. Solid line shows the 90% upper confidence limit for pure misalignments. Dashed line refers to the location for which the false signal by misalignments is equal to an EDM signal corresponding to ηEDM = 10-4.
This value corresponds to an EDM magnitude of dd ≈ 5∙10-19 e cm.
Courtesy: M. Rosenthal

18. Preparation for Improved Closed-Orbit Correction
Horizontal closed-orbit
Random positioning and rotation errors of dipoles and quadrupoles Gaussian distributed. For each point 1000 seeds. Dashed line: measured “rms” orbit at COSY. p0: slop of linear fit.
New survey of COSY has been provided and discussed.
Alignment procedure will be performed soon.
Upgrade of beam position monitor electronics also in preparation.
(Alignment accuracy of 0.2 mm is possible).
Courtesy: V. Schmidt

19. RF 𝑬×𝑩 Wien filter: Strip line design
In cooperation with RWTH Aachen

20. Clamps for the Ferrit cage
New RF Wien Filter
BPM
(Rogowski coil)
Copper
electrodes
Vacuum vessel with
small angle rotator
Clamps for the Ferrit cage
Ferrit cage
Beam pipe (CF 100)
Support structure
for electrodes
Inner support
tube
Support for geodetics RF
feedthrough
Ferrit cage
Mechanical
support
Magnetic fields were modelled with an accuracy of 10-6.

21. Electrostatic Deflector Development
Courtesy K. Grigoryev

22. Polarimeter Development
The current engineering drawing (detector and the target chamber). From left to right there are two cross type flanges, one for beam position monitors (BPM's) and the second one for the target. In the middle there is a vacuum chamber. Next, the two layer of φ-sensitive plastic scintillator and the LYSO HCAL are placed to absorb the total energy of the scattered particles.
LYSO calorimeter module in the carbon fiber enclosure.
Courtesy: I Keshelashvilli

23. Quadrant signals of Rogowski coil sensitive to beam position.
Challenge BPMs: Rogowski coil
Integral signal measures beam current
Quadrant signals sensitive to position
EDM experiment needs bunched beams
Rogowski coils well suited
Small size allows flexible installation up
left
right
down
Quadrant signals of Rogowski coil sensitive to beam position.

24. Rogowski Type Beam Position Monitor
Half and quarter winded Rogowski coils in the defined coordinate system. The shown configuration on the left enables a position measurement in x-direction.
The configuration shown on the right corresponds to a measurement in both directions: x and y.
Test of the linearity of the BPM response to the corrector magnet excitation, which is proportional to a horizontal beam displacement at the BPM.
Courtesy: F. Hinder, F. Trinkel

25. Highlights Experimental Achievements at COSY
Record In-Plane Polarization Lifetime
Ultra-High Precision Spin Tune Measurement
Spin-tune Based Feedback System
Progress of Technical Developments
Novel Waveguide RF Wien Filter
Electrostatic Deflector Development
Polarimeter Development
Rogowski Type Beam Position Monitor
Beam and Spin Dynamics
Systematic Limitations for EDM Measurements at COSY
Investigation of Lattices for a Deuteron EDM Ring

27. Conclusion Zusammenfassung Achievements:
- Spin tune measurement with precision of in a single cycle
- Long spin coherence time of more than 1000s
- Spin tracking codes developed and benchmarked
- Investigation of systematic limit for resonance methods
Goals:
- Beam and spin dynamics studies at COSY
- First direct EDM measurement at COSY
- R&D work and design study for dedicated EDM storage ring 27

28. Source(s) for EDMs Multiple experimental input is required …
… to disentangle the fundamental source(s) of EDMs

29. JEDI R&D Program (Jülich Electric Dipole Moment Investigations)
1. Studies of spin coherence time (SCT)
Phase space cooling and adjusting sextupole settings at COSY to reach a SCT of 1000 s
2. Investigation of systematic effect
Alignment of the ring magnets and closed-orbit correction
Opening angle of spin ensemble
3. Development and benchmark precision simulation programs for spin dynamics in storage rings
COSY-Infinity, integrating code and COSY experiments for bench marking
4. Development of high-efficiency polarimetry and high-precision BPMs
5. ExB Deflector development

30. Ultra-High Precision Spin Tune Measurement
(a) Polarization phase, or direction, in the plane of the ring as a function of time during an experiment along with a quadratic polynomial fit.
(b)The deviation of the spin tune from a reference value of along with an error band based on the statistical precision shown in the upper panel. At about 38 s, the most precise spin tune value is ( ± 9.7) ∙10-11.
Courtesy: D. Eversmann

31. Design of a Novel Waveguide RF Wien Filter
Magnetic fields were modelled with an accuracy of 10-6.
Design model of the RF Wien filter showing the parallel-plates waveguide and the support structure. 1: BPM; 2: copper electrodes; 3: vacuum vessel; small angle rotor; 4: clamps to hold the ferrite cage; 5: belt drive for 90° rotation, with a precision of 0.01° (0.17 mrad); 6: ferrite cage; 7: CF100 feedthrough; 8: support structure of the electrodes; 9: inner support tube.
Courtesy: A. Nass

32. History of Neutron EDM Limits
Smith, Purcell, Ramsey PR 108, 120 (1957)
RAL-Sussex-ILL (dn  2.9 10-26 ecm) PRL 97, (2006)
50 years of effort
Adopted from K. Kirch

33. Different shape of the electrodes
Electrostatic deflectors: Some results
Different shape of the electrodes
Material : Stainless steel, Aluminum
Mechanical polished and cleaned
Stainless steel
Two small half-spheres (R = 10mm)
17kV at 1mm distance → 17 MV/m
Half-sphere vs. flat surface
12kV at 0.05 mm distance → 240 MV/m
Aluminum
3kV at 0.1mm distance → 30 MV/m