Charged Particle Electric Dipole Moment Searches in...
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Charged Particle Electric Dipole MomentSearches in Storage Rings
J. PretzRWTH Aachen & FZ Jülichfor the JEDI collaboration
PSTP Bochum, September 2015
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Outline
Introduction: Electric Dipole Moments (EDMs):What is it?Why is it interesting?What do we know about EDMs?Experimental Method:How to measure charged particle EDMs?Results of first test measurements:Spin Coherence time and Spin tune
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What is it?
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Electric Dipoles
Classical definition:
~d =∑
i
qi~ri
−
+
~r1
~r2
~0
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Order of magnitude
atomic physics hadron physics
charges e
e
|~r1 −~r2| 1 Å= 10−8cm
1fm = 10−13cm
EDM
naive expectation 10−8e · cm
10−13e · cm
observed water molecule
neutron
2 · 10−8e· cm
< 3 · 10−26e· cm
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Order of magnitude
atomic physics hadron physics
charges e e
|~r1 −~r2| 1 Å= 10−8cm 1fm = 10−13cm
EDM
naive expectation 10−8e · cm 10−13e · cm
observed water molecule neutron
2 · 10−8e· cm < 3 · 10−26e· cm
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Neutron EDM
− 13 − 1
3
23
~d
2 · rn≈ 10−13cm
neutron EDM of dn = 3 · 10−26e·cm corresponds to separationof u− from d−quarks of ≈ 5 · 10−26cm
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Operator ~d = q~r
is odd under parity transformation (~r → −~r ):
P−1~dP = −~d
Consequences:In a state |a
⟩of given parity the expectation value is 0:
⟨a|~d |a
⟩= −
⟨a|~d |a
⟩
but if |a⟩
= α|P = +⟩
+ β|P = −⟩
in general⟨
a|~d |a⟩6= 0⇒ i.e. molecules
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EDM of molecules
xy
z
N
H
HH
z
Ψ1
xy
z
NH
HH
z
Ψ2
ground state: mixture of Ψs = 1√2
(Ψ1 + Ψ2) , P = +
Ψa = 1√2
(Ψ1 −Ψ2) , P = −
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EDMs & symmetry breaking
Molecules can have large EDM because of degeneratedground states with different parity
Elementary particles (including hadrons) have a definite parityand cannot posses an EDMP|had >= ±1|had >
unless
P and time reversal T invariance are violated!
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EDMs & symmetry breaking
Molecules can have large EDM because of degeneratedground states with different parity
Elementary particles (including hadrons) have a definite parityand cannot posses an EDMP|had >= ±1|had >
unless
P and time reversal T invariance are violated!
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EDMs & symmetry breaking
Molecules can have large EDM because of degeneratedground states with different parity
Elementary particles (including hadrons) have a definite parityand cannot posses an EDMP|had >= ±1|had >
unless
P and time reversal T invariance are violated!
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T and P violation of EDM
+
−
~d
~s
~µ
−
+
+
−
P
T
⇒ EDM measurement tests violation of fundamentalsymmetries P and T (
CPT= CP)
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~d : EDM~µ: magnetic momentboth || to spin
H = −µ~σ · ~B−d~σ · ~ET : H = −µ~σ · ~B+d~σ · ~EP : H = −µ~σ · ~B+d~σ · ~E
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Symmetry (Violations) in Standard Model
electro-mag. weak strong
C X E X
P X E (X)
T CPT→ CP X (E) (X)
C and P are maximally violated in weak interactions(Lee, Yang, Wu)CP violation discovered in kaon decays (Cronin,Fitch)described by CKM-matrix in Standard ModelCP violation allowed in strong interaction but correspondingparameter θQCD / 10−10 (strong CP-problem)
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Sources of CP−Violation
Standard Model
Weak interaction
CKM matrix → unobservably small EDMs
Strong interaction
θQCD → best limit from neutron EDM
beyond Standard Model
e.g. SUSY → accessible by EDM measurements
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Why is it interesting?
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Matter-Antimatter Asymmetry
Excess of matter in the universe:
observed SM prediction
η =nB−nB
nγ6× 10−10 10−18
Sakharov (1967): CP violation needed for baryogenesis
⇒ New CP violating sources beyond SM needed to explain thisdiscrepancy
They could manifest in EDMs of elementary particles
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What do we know aboutEDMs?
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History of Neutron EDM
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EDM: Current Upper Limits
electron (YbF, ThO)
muontau neutron
Hg)199
proton (Λ deuteron
cm
•ed
m/e
-3910
-3710
-3510
-3310
-3110
-2910
-2710
-2510
-2310
-2110
-1910
-1710
-1510
=0)QCDθ
Standard Model (
<1)CPϕ<π
αSUSY (
FZ Jülich: EDMs of charged hadrons: p,d , 3He
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EDM: Current Upper Limits
electron (YbF, ThO)
muontau neutron
Hg)199
proton (Λ deuteron
cm
•ed
m/e
-3910
-3710
-3510
-3310
-3110
-2910
-2710
-2510
-2310
-2110
-1910
-1710
-1510
=0)QCDθ
Standard Model (
<1)CPϕ<π
αSUSY (
Goal exp. ate cm)-24COSY (10
Goal dedicatede cm)-29ring (10
FZ Jülich: EDMs of charged hadrons: p,d , 3He
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Why Charged Particle EDMs?
no direct measurements for charged hadrons existpotentially higher sensitivity (compared to neutrons):
longer life time,more stored protons/deuterons
complementary to neutron EDM:dd
?= dp + dn ⇒ access to θQCD
EDM of one particle alone not sufficient to identifyCP−violating source
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Sources of CP Violation
Neutron, Proton
Nuclei: 2H, 3H,3He
Molecules: YbF, ThO, HfF+
Paramagne?c atoms: Tl, Cs
Diamagne?c atoms:
Hg, Xe, Ra
Leptons: muon
QCD
(including θ-‐term)
gluon chromo-‐EDM
lepton-‐quark operators
four-‐quark operators nu
clear theo
ry
quark chromo-‐EDM
lepton EDM
quark EDM
FUNDAMEN
TAL TH
EORY
atom
ic th
eory
J. de Vries
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How to measure chargedparticle EDMs?
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Experimental Method: Generic Idea
For all EDM experiments (neutron, proton, atoms, . . . ):Interaction of ~d with electric field ~E
For charged particles: apply electric field in a storage ring:
~E~s
d~sdt∝ d ~E × ~s
In general:
d~sdt
= ~Ω×~s
build-up of vertical polarization s⊥ ∝ |d |
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Experimental Requirements
high precision storage ring( alignment, stability, field homogeneity)high intensity beams (N = 4 · 1010 per fill)polarized hadron beams (P = 0.8)large electric fields (E = 10 MV/m)long spin coherence time (τ = 1000 s),polarimetry (analyzing power A = 0.6, acc. f = 0.005)
σstat ≈1√
Nf τPAE⇒ σstat(1year) = 10−29 e·cm
challenge: get σsys to the same level
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Systematics
Major source:Radial B field mimics an EDM effect:
Difficulty: even small radial magnetic field, Br can mimicEDM effect if :µBr ≈ dEr
Suppose d = 10−29e·cm in a field of Er = 10MV/mThis corresponds to a magnetic field:
Br =dEr
µN=
10−22eV3.1 · 10−8eV/T
≈ 3 · 10−17T
Solution: Use two beams running clockwise and counterclockwise, separation of the two beams is sensitive to Br
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Systematics
mgmg
eEv
eEvevBr
−evBr
Sensitivity needed: 1.25 fT/√
Hz for d = 10−29 e cm(possible with SQUID technology)
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Spin Precession: Thomas-BMT Equation
d~sdt = ~Ω× ~s = e
m [G~B+(
G − 1γ2−1
)~v × ~E+ m
e s d(~E+~v × ~B)]× ~s
Ω: angular precession frequency d : electric dipole momentG: anomalous magnetic moment γ: Lorentz factor
COSY: pure magnetic ringaccess to EDM via motional electric field ~v × ~B,requires additional radio-frequency E and B fieldsto suppress G~B contribution
neglecting EDM term
spin tune: νs ≈ |~Ω||ωcyc| = γG, (~ωcyc = e
γm~B)
BMT: Bargmann, Michel, Telegdi
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Spin Precession: Thomas-BMT Equation
d~sdt = ~Ω× ~s = e
m [G~B+(
G − 1γ2−1
)~v × ~E+ m
e s d(~E+~v × ~B)]× ~s
Ω: angular precession frequency d : electric dipole momentG: anomalous magnetic moment γ: Lorentz factor
dedicated ring: pure electric field,
freeze horizontal spin motion(
G − 1γ2−1
)= 0
COSY: pure magnetic ringaccess to EDM via motional electric field ~v × ~B,requires additional radio-frequency E and B fieldsto suppress G~B contribution
neglecting EDM term
spin tune: νs ≈ |~Ω||ωcyc| = γG, (~ωcyc = e
γm~B)
BMT: Bargmann, Michel, Telegdi
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Spin Precession: Thomas-BMT Equation
d~sdt = ~Ω× ~s = e
m [G~B+(
G − 1γ2−1
)~v × ~E+ m
e s d(~E+~v × ~B)]× ~s
Ω: angular precession frequency d : electric dipole momentG: anomalous magnetic moment γ: Lorentz factor
COSY: pure magnetic ringaccess to EDM via motional electric field ~v × ~B,requires additional radio-frequency E and B fieldsto suppress G~B contribution
neglecting EDM term
spin tune: νs ≈ |~Ω||ωcyc| = γG, (~ωcyc = e
γm~B)
BMT: Bargmann, Michel, Telegdi
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Spin Precession: Thomas-BMT Equation
d~sdt = ~Ω× ~s = e
m [G~B+(
G − 1γ2−1
)~v × ~E+ m
e s d(~E+~v × ~B)]× ~s
Ω: angular precession frequency d : electric dipole momentG: anomalous magnetic moment γ: Lorentz factor
COSY: pure magnetic ringaccess to EDM via motional electric field ~v × ~B,requires additional radio-frequency E and B fieldsto suppress G~B contribution
neglecting EDM term
spin tune: νs ≈ |~Ω||ωcyc| = γG, (~ωcyc = e
γm~B)
BMT: Bargmann, Michel, Telegdi
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Results of first testmeasurements
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Cooler Synchrotron COSY
COSY provides (polarized ) protons and deuterons withp = 0.3− 3.7GeV/c⇒ Ideal starting point for charged particle EDM searches
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COSY
Polarized proton & deuterons
Polarimeter
RF E × B dipole RF solenoid
cooled beams: e-cooling,
stochastic cooling
sextupoles
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R & D at COSY
maximize spin coherence time (SCT)precise measurement of spin precession (spin tune)rf- Wien filter design and construction
tests of electro static deflectors (goal: field strength > 10MV/m)development of high precision beam position monitorspolarimeter development
spin tracking simulation tools
E. Stephenson: Deuteron polarimeter developmentsfor a storage ring EDM search
I. Keshelashvili: Towards EDM PolarimetryN. Hempelman: FPGA-Based Upgrade of the Read-Out
Electronics for the Low EnergyPolarimeter at COSY/Jülich
S. Mey: Spin Manipulation with an RF Wien-Filter at COSYJ. Slim: Towards a High-Accuracy RF Wien Filter
for Spin Manipulation at COSY Jülich
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R & D at COSY
maximize spin coherence time (SCT)precise measurement of spin precession (spin tune)rf- Wien filter design and construction
tests of electro static deflectors (goal: field strength > 10MV/m)development of high precision beam position monitorspolarimeter development
spin tracking simulation tools
E. Stephenson: Deuteron polarimeter developmentsfor a storage ring EDM search
I. Keshelashvili: Towards EDM PolarimetryN. Hempelman: FPGA-Based Upgrade of the Read-Out
Electronics for the Low EnergyPolarimeter at COSY/Jülich
S. Mey: Spin Manipulation with an RF Wien-Filter at COSYJ. Slim: Towards a High-Accuracy RF Wien Filter
for Spin Manipulation at COSY Jülich
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R & D at COSY
maximize spin coherence time (SCT)precise measurement of spin precession (spin tune)rf- Wien filter design and construction
tests of electro static deflectors (goal: field strength > 10MV/m)development of high precision beam position monitorspolarimeter development
spin tracking simulation tools
E. Stephenson: Deuteron polarimeter developmentsfor a storage ring EDM search
I. Keshelashvili: Towards EDM PolarimetryN. Hempelman: FPGA-Based Upgrade of the Read-Out
Electronics for the Low EnergyPolarimeter at COSY/Jülich
S. Mey: Spin Manipulation with an RF Wien-Filter at COSYJ. Slim: Towards a High-Accuracy RF Wien Filter
for Spin Manipulation at COSY Jülich
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Experimental Setup
Inject and accelerate vertically polarized deuterons top ≈ 1 GeV/c
flip spin with help of solenoid into horizontal planeExtract beam slowly (in 100 s) on targetMeasure asymmetry and determine spin precession
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Experimental Setup
Inject and accelerate vertically polarized deuterons top ≈ 1 GeV/cflip spin with help of solenoid into horizontal plane
Extract beam slowly (in 100 s) on targetMeasure asymmetry and determine spin precession
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Experimental Setup
Inject and accelerate vertically polarized deuterons top ≈ 1 GeV/cflip spin with help of solenoid into horizontal planeExtract beam slowly (in 100 s) on targetMeasure asymmetry and determine spin precession
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Asymmetry Measurements
Detector signal Nup,dn ∝ (1± P A sin(γGωrev t))
Aup,dn =Nup − Ndn
Nup + Ndn = P A sin(γGωrev t)
A: analyzing power, P : polarization
Aup,dn = 0
spin
~pC
Aup,dn = PA
spin
~pC
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Polarimetry
Cross Section &Analyzing Powerfor deuterons
Nup,dn ∝(1± P A sin(νsωrev t))
Aup,dn =Nup − Ndn
Nup + Ndn
= P A sin(νsωrev t)
A : analyzing powerP : beam polarization
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Polarimeterelastic deuteron-carbon scatteringUp/Down asymmetry ∝ horizontal polarization→ νs = γGLeft/Right asymmetry ∝ vertical polarization→ d
spin
Nup,dn ∝ 1± PA sin(νsωrev t), frev ≈ 750 kHz
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Up - dn asymmetry Aup,dn
Aup,dn(t) = AP0e−t/τ sin(νsωrev t + ϕ)
τ → spin decoherenceνs → spin tune
time scales: νsfrev ≈ 120 kHz
τ in the range 1-1000 s
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Polarization Flip
time in s80 100 120 140 160 180 200
y P
∝L
eft-
Rig
ht-A
sym
met
ry
-0.3
-0.2
-0.1
0
0.1
0.2
0.3
time in s80 100 120 140 160 180 200
x P
∝U
p-D
own-
Asy
mm
etry
-0.1
-0.05
0
0.05
0.1
0.15
0.2
0.25
0.3
enve
lope
of
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Polarization Flip
time in s80 100 120 140 160 180 200
y P
∝L
eft-
Rig
ht-A
sym
met
ry
-0.3
-0.2
-0.1
0
0.1
0.2
0.3
time in s80 100 120 140 160 180 200
x P
∝U
p-D
own-
Asy
mm
etry
-0.1
-0.05
0
0.05
0.1
0.15
0.2
0.25
0.3
x
z
y
enve
lope
of
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Polarization Flip
time in s80 100 120 140 160 180 200
y P
∝L
eft-
Rig
ht-A
sym
met
ry
-0.3
-0.2
-0.1
0
0.1
0.2
0.3
time in s80 100 120 140 160 180 200
x P
∝U
p-D
own-
Asy
mm
etry
-0.1
-0.05
0
0.05
0.1
0.15
0.2
0.25
0.3
x
z
y
enve
lope
of
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Results: Spin Coherence Time (SCT)
Short Spin Coherence Time
/ ndf 2χ 69.29 / 90
Amplitude 0.006± 0.282
SCT
1- 0.00145± -0.04968
time[s]0 10 20 30 40 50 60 70 80 90
UD
Asy
mm
etry
0
0.05
0.1
0.15
0.2
0.25 / ndf 2χ 69.29 / 90
Amplitude 0.006± 0.282
SCT
1- 0.00145± -0.04968
Horizontal Asymmetry Run: 2042
unbunched beam∆p/p = 10−5 ⇒ ∆γ/γ = 2 · 10−6,Trev ≈ 10−6 s⇒ decoherence after < 1 sbunched beam eliminates 1st order effects in ∆p/p⇒ SCT τ = 20 s
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Results: Spin Coherence Time (SCT)
Long Spin Coherence Time
/ ndf 2χ 93.9 / 90
Amplitude 0.0016± 0.2667
SCT
1- 0.000149± -0.002628
time[s]0 10 20 30 40 50 60 70 80 90
UD
Asy
mm
etry
0.05
0.1
0.15
0.2
0.25
/ ndf 2χ 93.9 / 90
Amplitude 0.0016± 0.2667
SCT
1- 0.000149± -0.002628
Horizontal Asymmetry Run: 2051
SCT of τ =400 s, after correction with sextupoles(chromaticities ξ ≈ 0)
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Longer cycle
Preliminaryenve
lope
of
(data taken a few weeks ago)
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Spin Tune νs
Spin tune: νs = γG =nb. of spin rotations
nb. of particle revolutions
~s ~p
⊙ ~B
2πγG
deuterons: pd = 1 GeV/c ( γ = 1.13), G = −0.14256177(72)
⇒ νs = γG ≈ −0.16152 / 60
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Up - dn asymmetry Aup,dn
Long SCT τ allows now to observe νs(t)≈γG,respectively ϕ(t)
Aup,dn(t) = AP0e−t/τ sin(νs(t)ωrev t + ϕ)
= AP0e−t/τ sin(ν0sωrev t + ϕ(t))
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Phase vs. turn number
]6
number of particle turns [10
0 10 20 30 40 50 60 70
[ra
d]
ϕ∼
2
3
4
time [s]
0 20 40 60 80
|ν0s |
0.160975405
0.160975407
0.160975409
|νs(t)| = |ν0s |+
1ωrev
dϕdt
⇒ |νs(38 s)| = (16 097 540 628.3± 9.7)× 10−11
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Spin Tune Measurement
precision of spin tune measurement 10−10 in one cycle(most precise spin tune measurement)Compare to muon g − 2: σνs ≈ 3 · 10−8 per yearmain difference: measurement duration 600µs comparedto 100 sspin rotation due to electric dipole moment:
νs =vmγd
es= 5 · 10−11 for d = 10−24e cm
(in addition rotations due to G and imperfections)spin tune measurement can now be used as tool toinvestigate systematic errors
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Spin Tune jumps
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Spin Tune for different cycles
time [s]0 500 1000 1500
]9
[10
sν ∆
15
10
5
0
5
10 Preliminary
upξP
downξP
∆νs = 10−8 → ∆p/p ≈ 10−7
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JEDI Collaboration
JEDI = Jülich Electric Dipole Moment Investigations≈ 100 members(Aachen, Bonn, Daejeon, Dubna, Ferrara, Grenoble,Indiana, Ithaca, Jülich, Krakow, Michigan, Minsk,Novosibirsk, St. Petersburg, Stockholm, Tbilisi, . . . )≈ 10 PhD studentsclose collaboration with srEDM collaboration in US/Korea
http://collaborations.fz-juelich.de/ikp/jedi/index.shtml59 / 60
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Summary & Outlook
EDMs of elementary particles are of high interest todisentangle various sources of CP violation searched forto explain matter - antimatter asymmetry in the UniverseEDM of charged particles can be measured in storageringsExperimentally very challenging because effect is tinyFirst promising results from test measurements at COSY:spin coherence time: few hundred seconds
spin tune: 10−10 in 100 s
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