1. electric dipole moments (EDM)
Static and oscillating
Hans ströher I Matter and the universe days 2019 (desy)

2. Electric dipole moments
Introduction
EDM: a permanent separation of positive and negative charge
(vector along spin direction)
Fundamental property of particles (like mass, charge, magnetic
moment)
Existence of EDM only possible if violation of time reversal
and parity symmetry; note:
Close connection to matter-antimatter asymmetry of Universe
Sensitive to new physics beyond the Standard Model
Axion field (coupling to gluons) leads to oscillating EDM

3. Electric dipole moments
Experimental effort
Original by Klaus Jungman

4. Electric dipole moments
Measurements – status and prospects
New: charged particles
(proton, deuteron …)
Potentially highest
sensitivity
Identification of source
requires neutron and
proton (maybe even
deuteron …) p
Current proton limit > neutron;
only indirect measurement (199Hg)

5. Electric dipole moments
Measurement principle (charged particles)
Longitudinally polarized beam in
storage ring
Radial electric field interacting with
EDM (torque)
Observable: slow rotation of spin
direction ( polarimetry)
Thomas-BMT eq.:
Ideal situation: B = 0, magic momentum  WMDM = 0 („frozen spin“)

6. Electric dipole moments
Sensitivities
Statistical sensitivity (one cycle):
cycles (w/ parameters of table):
Challenge:
Identify and suppress all systematic errors to the same level!

7. Electric dipole moments
Systematic errors – one example
Major source: radial magnetic field Br
 mimics EDM, if m Br ~ d Er
Order of magnitude estimate:
assume d = e cm, Er = 10 MV/m
Corresponding magnetic field Br: !
Potential solution:
Use two beams running clockwise and counter-clockwise
 Separation of the two beams is sensitive to Br

8. Electric dipole moments
Vision – a dedicated precision pEDM storage ring
Electrostatic ring (at least 4 beam bunches)
Running at magic momentum (p = 0.7 GeV/c)
Counter-rotating beams (simultaneously, same
orbit)  many systematic effects cancel
 Many open questions, e.g.:
Intensity and spin coherence time
Injection, phase space cooling of the beams
Polarimetry, orbit control, shielding, …
General: ideal  realistic machine (tolerances)
Staged approach

9. Electric dipole moments
Staged approach
COSY

10. Electric dipole moments
Stage-0: recent achievements at COSY (JEDI collaboration)
Precise determination of spin tune
PR ST-AB (2014), PRL (2015)
Long spin coherence time
PRL (2016)
Phase-lock of spin precession
PRL (2017)
Polarimeter development
Beam instrumentation
RF-Wien filter development
COSY is world-wide unique to perform these measurements

11. Electric dipole moments
Stage-0: recent achievements at COSY (JEDI collaboration)
Precise determination of spin tune
PR ST-AB (2014), PRL (2015)
Long spin coherence time
PRL (2016)
Phase-lock of spin precession
PRL (2017)
Polarimeter development
Beam instrumentation
RF-Wien filter development
COSY is world-wide unique to perform these measurements

12. Electric dipole moments
Stage-1: precursor experiment at COSY
COSY (magnetic storage
ring)  spin precession;
use of deuteron beams
Problem: no EDM effect
RF Wien Filter:
RF-fields such that
forward-backward
effect does not cancel
Sensitivity to EDM
Wien Filter
EDM (or a field in x):
rotates in x-direction
(...)
2D map … should have
minimum at (0,0) d = 0
or away from (0,0) d > 0
RF Wien Filter
invariant spin axis:
d = d > 0
Exptl. data (Dec.2018)
COSY ?
First-ever deuteron EDM measurement
Statistical sensitivity 10-(23-24) e cm; systematics: imperfections, alignment, …  limit: ~ e cm
systematics: imperfections, alignment, …  limit: ~ e cm

13. Electric dipole moments
Stage-2: prototype ring
30 MeV all-electric p ring
Storage time
CW/CCW operation
Spin coherence time
Polarimetry
Phase space cooling
mp effects
Option: add B-field, 45 MeV
pEDM measurement
 Possible host: COSY
Inevitable next step

14. Electric dipole moments
Stage-3: precision EDM ring
All-electric deflection
Magic momentum (p = 701 MeV/c)
Simultaneous CW/CCW beams
Phase-space cooled beams
Long spin coherence time (> 1000 s)
Non-destructive precision polarimetry
Optimum orbit control
Optimum shielding of external fields
Control of residual (intentional) Br field
„Holy Grail“ of storage rings (largest ever conceived)

15. Electric dipole moments
Staged approach
Step 1:
Precursor
Now
5 yrs
10 yrs
Step 2:
Prototype
Step 3:
Final ring p
Submission to ESPP Update

16. Electric dipole moments - oscillating
Interaction of coherently oscillating axion DM field with gluons … oEDM
Static EDM: accumulation
in „frozen spin“ condition
Oscillating EDM:
spin precesses, but oEDM flip
 right frequency: accumulation
frequency (axion mass) not
known  resonance scan
Phase unknown
static EDM (see above)
now: oscillating EDM
Oscillating EDM easier to detect (resonance)
Proof-of-principle possible at COSY
Axion (DM) / oEDM: additional science case for CPEDM

17. Electric dipole moments
Summary
Electrostatic storage rings offer a unique possibility to search for important new physics (EDM, DM)
Ongoing: precursor experiment at COSY (RF Wien filter)
Next step: prototype ring (design study under preparation)
Long-term vision: precision storage ring (CW/CCW, magic momentum)
Projects discussed in the framework of Physics Beyond Colliders (PBC) at CERN
Input for update of European Strategy for Particle Physics (ESPP)
00 Month 2018

19. Electric dipole moments
Experimental EDM limits

20. Electric dipole moments
Experimental EDM limits

21. Electric dipole moments
Why so many (different) experiments?
Experiments
Theoretical analysis
Sources
Ultimate goal

22. Electric dipole moments
Dark Matter – accessible frequency/mass range