New Insights into Spin Coherence Time

Based onA.Lehrach (FZJ), B. Lorentz (FZJ), W. Morse (BNL),

N.Nikolaev (Landau Inst) & F. Rathmann (FZJ)& EDM COSY Workshops

& EDM-BNL & JEDI Teleconferences

More from Ed Stephenson, Greta Guidoboni, Yannis Semertzidis,

Yurii Orlov, Frank Rathmann, Alfredo Lucciaand others at this Workshop

EDM, ECT*, Trento, 2 October 2012

Layout:• Why the EDM and at which accuracy?• TF-BMT equation and EDM signal with frozen horizontal

(longitudinal) spin• The alternative and precursor: EDM signal from idly precessing

horizontal spin at all magnetic COSY with RF E-fields

• Spin tune with momentum spread and Spin Coherence Time • RFE(B)-flipper: shall a new element in a ring destroy spin

coherence?• Spin Decoherence-free magic energies and flattop RFE flipper

• Semertzidis & Orlov (and NNN & Silenko)EDM-transparent Wien filter is equivalent to the MDM-transparent RFE flipper

• Betatron Oscillations, Path Lengthening, Spin Tune Chromaticity and all that: ad to Greta Guidoboni‘s talk (also recall Novosibirsk -1987)

• dEDM and pEDM can for the first time be constrained at COSY reaching the ballpark of modern theory predictions

Electric dipole moment (EDM)

A permanent EDM of a fundamental particle violates both parity (P) and

time reversal symmetry (T).

Assuming CPT to hold, the combined symmetry CP is violated as well.

Future: Search for Electric Dipole Moments

Frank Rathmann 319th International Spin Physics Symposium

Importance of Spin Coherence Time

for EDM Searches A.Lehrach (FZJ), B. Lorentz (FZJ),

B.W.Morse (BNL), N.Nikolaev (FZJ & Landau Inst)

F.Rathmann (FZJ)

RWTH / IKP FZJ, 3 May 2012

Upper bounds on the neutron EDM

2011 2012 2013 2014 2015 2016 2017 201810-28

10-27

10-26

10-25

multi-chamber @ PNPI super UCN source

double-chamber @ PNPI super UCN source

double-chamber @ ILL UCN source with superfluid He

double-chamber @ ILL EDM position

Neutron E

DM

Exp

erim

enta

l lim

it, e

·cm

Year

double-chamber @ ILL MAM position

PNPI-ILL-PTI collaboration (Serebrov et al)Prospects to increase sensitivity of EDM

measurements

Gatchina EDM spectrometer 1975

Gatchina EDM spectrometer at ILL

NEW: EDM search in time development of spin in a storage ring:

A magic storage ring for protons (electrostatic), deuterons, …

“Freeze“ horizontal spin precession; watchfor development of a vertical component !

8

Future: Search for Electric Dipole Moments

particle p (GeV/c) E (MV/m) B (T)

proton 0.701 16.789 0.000

deuteron 1.000 -3.983 0.1603He 1.285 17.158 -0.051

One machine with r~30 m

Polarized beam in all magnetic ring

A

AS

one particle with magnetic moment

“spin tune”

“spin closed orbit vector”COn̂

s2

AS

ring

makes one turn

Vertical stable polarization vs. idle precession of the horizontal one with the momentum dependent spin tune

9

Spin coherenceWe usually don‘t worry about coherence of spins along the rotation axis

COn̂

At injection all spin vectors aligned (coherent)

After some time, spin vectors get out of phase and fully populate the cone

Polarization not affected!

Situation very different, when you deal with S

COn̂

COn̂

At injection all spin vectors aligned After some time, the spin vectors are all out of phase and in the horizontal plane

Longitudinal polarization vanishes!

In an EDM machine with frozen spin, observation time is limited.

Spin coherence time: 103 s for measurement on 10-29 e·cm level

Extreme cases of phase slips:• Random effects in the momentum spread give finite SCT• Regular synchrotron oscillations do not decohere horizontal spin:

infinite SCT?• Rectangular (flat-top) excitation of a flipper suppresses

dangerous flipper phase slip effects (A. Lehrach et al. 2011): to be tested at COSY

• Spin tune and flipper phase slips are of the same origin cancellations at magic energies and flipper harmonics, to be tested at COSY (A. Lehrach et al. 2011)

• Runaway decoherence from the path lengthening by betatron oscillations (Ed Stephenson et al. 2012: Successfully learning to tame them at COSY. Also derive lessons from Novosibirsk-1987)

• New development at COSY: fast time stamp in the polarimetry of rapidly precessing horizontal spin

Spin Coherence Time with RFE Flipper

• Possibility to increase spin coherence time by 3 to 5 orders of magnitude• Experiment with polarized COSY beam soon

Why EDM-transparent Wien-Filter?

• The motional E-field in a ring proper rotates EDM but with a constant amplitude

• MDM-transparent RFE filter Lorentz force & unwanted excitation of coherent betarton oscillations and perhaps a runaway decoherence

• Wien filter eliminates the E-field on EDM• 2012: Y. Semertzidis & Yu. Orlov (also NNN and A.Silenko): EDM-

transparent Wien-filter in a COSY ring still generates the EDM signal

• The reason: Wien-filter is MDM-nontrasparent and gives rise to a frequency modulation of the spin tune which conspires with the motional E-field in a ring. The EDM signal is the same as for MDM-transparent flipper

• The spin decoherence properties of the two devices are the same

• Run the radial RFB flipper in the Wien-filter mode

Spin Dynamics for EDM

at COSYA.Lehrach (FZJ), B. Lorentz (FZJ,

B.W.Morse (BNL), N.Nikolaev (FZJ & Landau Inst)

F.Rathmann (FZJ)

PNPI Winter School, Rajvola, 01.02. 2012

Path lengthening & spin tune spread runaway decoherence

• Greta Guidoboni, COSY expt on idle precession: taming spin tune spread by sextupole magnets

• Find ways to randomize the betatron oscillation amplitude of individual particles

• Future expts at COSY: How will tampering the chromaticity work with running RFE flipper?

Outlook

• Much progress in understanding SCT at COSY• Suppression of spin decoherence from

longitudinal momentum spread at special (magic) energies

• Taming spin tune spread effects by fine tuning the chromaticity by sextupoles

• Away from runaway spin decoherence by randomizing the spin tune spread

• COSY constraints on pEDM & dEDM can reach the ballpark of theoretical expectations

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