1. Electric Dipole Moments PPAP community meeting 2015
Ben Sauer

2. A search for new physics.
EDMs of fundamental particles violate P and T symmetry.
Search for physics beyond the Standard Model (probes physics at many TeV).
T-violation = CP-violation
(via CPT).
CP-violation is a big mystery
in particle physics / cosmology.

3. CP from fields to particles to atoms
YbF, Cs
ThO*, HfF+
atom/molecule
level
Higgs
SUSY
Left/Right
T-weak
Strong CP
field theory
CP model
qGG
electron/quark
level
de, Cs dq
dcq
muon?
nuclear
level
NNNN
Schiff
moment
n, p
nucleon
level Hg
TlF ~

4. Neutron EDM nEDM UK is back in business!
After years in the cryogenic wilderness...
nEDM UK is back in business!
New systematic effect identified, confirmed
New diagnostic tool developed
Revised nEDM world limit
Major players in PSI-nEDM...
... which is now taking world-beating data
Publications!

5. Revised nEDM world limit
Further work (almost entirely by Sussex group) based on data used for 2006 limit:
Inclusion of new gravitation depolarization systematic
Inclusion of new information from subsequent measurements of apparatus components
Much improved calculation of spectrum, based on detailed Monte Carlo
Inclusion of new measurement of n to Hg gyromagnetic ratio & updated Hg EDM limit
Most comprehensive & detailed nEDM analysis ever submitted to PRD
Results in slight revision of limit: 2.9 3.0x10-26 e.cm
Scale of false EDM effect previously had to be adjusted to fit data – now (with grav depol) matches predictions well!

6. nEDM at PSI - www.neutronedm.org
nEDM now running with world-beating sensitivity of ~1.5x10-25 e.cm/day
Sussex taking leading role:
3He magnetometry work
Systematics, simulation, analysis
Robust backup to (unreliable) HV supply
Devised & coordinated data blinding
Harris appointed Chair of Collaboration Board
Blinded data-taking began Sept 13th 2015;
should exceed previous limit mid-2016

7. n2EDM at PSI Planned upgrade: Double Ramsey chamber system – measure
both E-field directions at once
Unprecedented systematics control
Geometry better matched to source: more neutrons
Magnetometry confined to ground planes; can increase HV
Much improved magnetic shielding
Should achieve sensitivity ~3Ex10-27 e.cm
SoI planned to be submitted in 2016; complete construction by 2020
this will ensure we stay ahead of competition

8. Competition: SNS nEDM at ORNL
Cryogenic storage of neutrons
Experiment in Critical Component Demonstration phase.
Data collection planned to start 2021

9. Proton EDM Limit from 1989 TlF experiment: 6x10-23 e.cm
Limit from Hg: 5x10-24 e.cm
A Storage Ring Experiment to detect a Proton Electric Dipole Moment
arxiv.org: v1
Proposal to directly measure pEDM in a storage ring
Work at ‘magic’ velocity at which spin precession matches momentum in ring (0.7 GeV/c)
Aim is to reach e.cm level

10. eEDM using YbF
YbF (or ThO*, or HfF+) molecule acts as amplifier for eEDM
© Jony Hudson

11. “Traditional” YbF eEDM
Compared to 2011 measurement:
Factor 3 for longer plates
Factor 2 for N=2 population pumping
Factor 5 for cycling detection
Factor 4 for slower beam
Johnson noise from electric field plates would limit sensitivity (moving to thin-film electrodes)
Two orders of magnitude improvement is underway, aiming for 3x10-29 e.cm
We have a lot of experience and a sophisticated data analysis scheme, so should be able to control systematic effects.

12. Longer term eEDM: YbF fountain4K
Fantastically inefficient: 10-8 from cell to detector. But T = 300ms, so 60h of data gives sd = 3x10-31 e.cm!

13. Current status of EDMs d(muon) < 1.9×10-19 d(proton) < 5×10-24
d [e.cm]
d(muon) < 1.9×10-19
neutron:
10-20
electron:
10-22
Left-Right
MSSM
Higgs
Multi
d(proton) < 5×10-24
10-24
d(neutron) < 3×10-26
YbF
10-26
10-28
d(electron) < 9×10-29
ThO
10-29
1960
1970
1980
1990
2000
2010
2020
2030

14. YbF: really large internal field
Parpia
Quiney
Kozlov
Titov
18 GV/cm
15 GV/cm
(2011) 15
Effective Field |hE| (GV/cm) 10 5 5 10 15 20 25 30
Applied Electric Field (kV/cm)
© Imperial College London

15. The YbF team Mike Tarbutt Ed Hinds
Jony Hudson Joe Smallman Isabel Rabey
B.E.S Jack Devlin
YbF fountain:
James Bumby
James Almond
Jongseok Lim
Noah Fitch

17. An EDM experiment E
Precess
time T
Analyze
Polarize

18. New systematic: Gravitational depolarisation & “Ramsey wrapping”
Average B field sampled depends on neutron energy
Low-energy tail gives asymmetric distribution of accumulated Ramsey phase
Ramsey frequency measurement is modulo 2p, so low tail can end up on high end of distribution! “Ramsey wrapping”
Causes nonlinearities in frequency response, depolarisation etc
Predicted in calculations by Sussex group in 2013
Now verified by comparison with data: publication imminent in PRD
Affects sytematic correction in nEDM analysis!
motional false edm signal
vs. n/Hg frequency ratio offset
Polarization vs. dB/dz
Without grav. depol.
With grav. depol.

19. UCN spin-echo: New diagnostic tool
Flip spins part way through Ramsey sequence. Spins that are “ahead” are sent to the back & vice-versa, to cancel dephasing. Changing pulse timing allows determination of neutron spectrum and B-field gradient offset.
Idea developed at PSI; Sussex group provided underlying analytic calculations & simulations of depolarisation processes
publication imminent in PRL (“Editor’s Choice” article)
We can now measure the neutron spectrum directly!