charged particle electric dipole moment searches in...

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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unless


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unless


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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

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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d~sdt = ~Ω× ~s = e

m [G~B+(

G − 1γ2−1

)~v × ~E+ m

e s d(~E+~v × ~B)]× ~s


dedicated ring: pure electric field,

freeze horizontal spin motion(

G − 1γ2−1

)= 0


neglecting EDM term


γm~B)


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d~sdt = ~Ω× ~s = e

m [G~B+(

G − 1γ2−1

)~v × ~E+ m

e s d(~E+~v × ~B)]× ~s



neglecting EDM term


γm~B)


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d~sdt = ~Ω× ~s = e

m [G~B+(

G − 1γ2−1

)~v × ~E+ m

e s d(~E+~v × ~B)]× ~s



neglecting EDM term


γm~B)


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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









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R & D at COSY









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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

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

http://collaborations.fz-juelich.de/ikp/jedi/index.shtml

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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charged particle electric dipole moment searches in...

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