The nEDM Experiment at the SNS

Christopher CrawfordUniversity of Kentucky

for the nEDM Collaboration

Symposium on Nuclear Physics XXXIII

Cocoyoc, Morelos, México2010-01-07

Outline

• EDM properties – scientific motivation• Properties of neutron – generation• Measurement technique – ILL experiment• Properties of He – new technique• Experimental setup – expected results

Electric Dipole Moment

+

-P or T reversed state

• EDM is a P and T (therefore CP) violating quantity

• Standard model value: dn ~ 10-32 – 10-31 e·cm

(Small! Ideal probe for new Physics)

• Present limit: dn < 2.8x10-26 e·cm (PRL 97, 131801 (2006))

+

-

Evolution of EDM Experiments

CP violation and New Physics

• In SM, quark EDM is zero to first order in GF (one loop), and is also zero at the two-loop level (cancellation among diagrams).

dn ~ 10-32 – 10-31 e·cm• Many extension of SM predict an extra set of particles and CP violating

phases (eg SUSY, LR symmetric model)

• These models predict substantially larger EDMs than SM• Neutron EDM is a very sensitive probe for new sources of CP violation

fL fLf’

W W

e+i e-i

Standard Model€

˜ f

€

˜ f

€

˜ γ €

€

fL

€

fR

€

e+iφL

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e−iφ R

SUSY

• Cosmic ray contains– consistent with secondary production by protons

• Matter-antimatter symmetry would imply

– both BBN and CMB anisotropy find:• Sakharov conditions:

– B violating interactions– CP and P violation– Departure from thermal equilibrium

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np /np ~ 10−4

€

NB

Nγ

=N

B

Nγ

~ 10−18 (kTcritical ≈ 20 MeV)

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NB

Nγ

≈10−9

Baryon Asymmetry of the Universe

EDM and CP Violation in QCD

• QDC Langrangian can in principle has a P- and T-violating term

• The term can generate a neutron EDM

• The current neutron EDM limit gives

• One proposed remedy, Peccei-Quinn symmetry, predicts axions. However, axions have not been observed.

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Lθ = θgs

2

32π 2˜ G μν Gμν

€

dn ~ O 10−16θ( ) e ⋅cm

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θ <10−9 Strong CP problem

Properties of the Neutron

mn = mp + me + 782 keV

n = 885.7 ± 0.8 s

qn < 2 x 10-21 e

dn < 3 x 10-26 e cm

n = -1.91 N

rm = 0.889 fm

re2 = -0.116 fm2

– 3 valence quarks + sea– exponential magnetization

distribution– pion cloud:

spin 1/2 isospin 1/2

pp nn

uud uddup down

data from BLAST

Neutron sources - ReactorsILL, Grenoble, France

Spallation Neutron Source (SNS)

• spallation sources: LANL, SNS– pulsed -> TOF -> energy

• LH2 moderator: cold neutrons– thermal equilibrium in ~30 interactions

Oak Ridge National Laboratory, Tennessee

Spallation Neutron Source (SNS) at ORNL

January 25, 20051 GeV, 1.4 mA Proton Linac

•SNS construction completed: 2006•SNS Total Project Cost: 1.411B$

Ultra-Cold Neutrons (UCN)

3mg

• slow enough to be completely reflected by 58Ni optical potential

kinetic: 8 m/sthermal: 4 mKwavelength: 50 nm

nuclear: 335 neV (58Ni)

magnetic: 60 neV (1 T)gravity: 102 neV (1 m)

BE

For B ~ 10mG = 30 Hz

For E = 50 kV/cm and dn= 10-28 e·cm = 5 nHz (precesses every 6.5 yr)(corresponds to a change in magnetic field of 2 x10-12 gauss)

€

hν = −[2μnB ± 2dn E]

dn =−hΔν

4E

δdn ∝1

r E NUCNTstorage

Principle of the Measurement

Ramsey’s method of separated oscillatory fields — “Traditional” method for nEDM

Initial state

/2 pulse

Free precessio

n

Second /2

pulseZ component

of nuclear spin

Spin flip oscillato

r frequen

cy

Slide courtesy of A. Esler and Sussex Neutron EDM group (ILL)

B field

Spin flip is most efficient when the spin arrives at the 2nd coil with the right phase, i.e. the phase advance of spin rotation is the same as the RF phase advance.

Frequency difference between spin flip field and spin’s Larmor precession makes the 2nd pulse be out of phase with the 1st.

J.H.Smith, E.M.Purcell, and N.F.Ramsey, Phys. Rev. 108, 120 (1957)

ILL Measurement

P.G. Harris et al., RPL 82, 904 (1999) C. A. Baker et al., PRL 97, 131801 (2006)

• Precession measurement:– Ramsey’s separated

oscillatory field magnetic resonance method

• Magnetometry:– Mercury co-magnetometer

• Neutron source:– Ultra-Cold Neutrons from

ILL reactor• Selected parameters:

– E=4.5kV/cm– Tstorage = 130s– N=15000

• Results– dn< 2.8x10-26 ecm (90%CL)

199Hg Co-Magnetometer

• Co-magnetometer: – Magnetometer that occupies the same volume over the

same precession time interval as the species on which an EDM is sought

Systematic effects due to the interaction of the vE field with B field gradients

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Br =r

2

∂BZ

∂z= arRadial gradient

Bv = v x E field changes sign with direction

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ω =−2av 2E

c ω02 −ωr

2( )

Particle following roughly circular orbit with orbital frequency ωr

•Pendlebury et al PRA 70 032102 (2004)•Lamoreaux and Golub PRA 71, 032104 (2005)•Barabanov, Golub, Lamoreaux, PRA 74, 052115 (2006)

After averaging over rotational direction

Need

€

1

Bz

∂Bz

∂z≈10−6 /cm at 10 mG

EDM CollaborationR. Alarcon, S. Balascuta, L. Baron-Palos

Arizona State University, Tempe, AZ, USAD. Budker, B. Park

University of California at Berkeley, Berkeley, CA 94720, USAG. Seidel

Brown University, Providence, RI 02912, USAE. Hazen, A. Kolarkar, V. Logashenko, J. Miller,

L. RobertsBoston University, Boston, MA 02215, USA

A. Perez-Galvan, J. Boissevain, R. Carr, B. Filippone,M. Mendenhall, R. Schmid

California Institute of Technology, Pasadena, CA 91125, USAM. Ahmed, M. Busch, W. Chen, H. Gao, X. Qian, Q. Ye,

W.Z. Zheng, X. F. Zhu, X. ZongDuke University, Durham NC 27708, USA

F. MezeiHahn-Meitner Institut, D-14109 Berlin, Germany

C.-Y. Liu, J. Long, H.-O. Meyer, M. SnowIndiana University, Bloomington, IN 47405, USA

L. Bartoszek, D. Beck, P. Chu, C. Daurer, A. Esler,J.-C. Peng, S. Williamson, J. Yoder

University of Illinois, Urbana-Champaign, IL 61801, USAC. Crawford, T. Gorringe, W. Korsch, B. Plaster, H. Yan

University of Kentucky, Lexington KY 40506, USAE. Beise, H. Breuer, T. Langford

University of Maryland, College Park, MD 20742, USA

P. Barnes, S. Clayton, M. Cooper, M. Espy, R. Hennings- Yeomans, T. Ito, M. Makela, A. Matlachov, E. Olivas, J.

Ramsey, I. Savukov, W. Sondheim, S. Tajima, J. Torgerson, P. Volegov, S. Wilburn

Los Alamos National Laboratory, Los Alamos, NM 87545, USAK. Dow, D. Hassel, E. Ihloff, J. Kelsey, R. Milner,

R. Redwine, J. Steele, E. Tsentalovich, C. VidalMassachusetts Institute of Technology, Cambridge, MA 02139,

USAJ. Dunne, D. Dutta, E. Leggett

Mississippi State University, Starkville, MS 39762, USAF. Dubose, R. Golub, C. Gould, D. Haase, P. Huffman,

E. Korobkina, C. Swank, A. YoungNorth Carolina State University, Raleigh, NC 27695, USA

R. Allen, V. Cianciolo, S. PenttilaOak Ridge National Laboratory, Oak Ridge, TN 37831, USA

M. HaydenSimon-Fraser University, Burnaby, BC, Canada V5A 1S6

N. Fomin, G. GreeneUniversity of Tennessee, Knoxville, TN 37996, USA

S. StanislausValparaiso University, Valparaiso, IN 46383, USA

S. BaesslerUniversity of Virgina, Charlottesville, VA 22902, USA

S. Lamoreaux, D. McKinsey, A. SushkovYale University, New Haven, CT 06520, USA

EDM Experiment at SNS

• General strategy: perform experiment in superfluid liquid 4He– Produce UCN in measurement cell via superthermal process– Use polarized 3He as comagnetometer– Use 3He-n interaction as spin precession analyzer

• Figure of merit:

• Expected gain over the ILL measurement

A 2 orders of magnitude overall gain in sensitivity is expected€

E NT

€

E ⇒ 5E T ⇒ 5T N ⇒ 100N

R.Golub and S.K.Lamoreaux Phys. Rep. 237, 1 (1994)

•8.9 Å cold neutrons get down-scattered in superfluid 4He by exciting elementary excitation

•Up-scattering process is suppressed by a large Boltzman factor

•No nuclear absorption

R.Golub and J.M.Pendlebury, Phys.Lett.A 62,337,(77)

Superthermal Production of UCN

• Expect a production of ~ 0.3 UCN/cc/s• With a 500 second lifetime, UCN~150/cc and NUCN~1.2x106 for

an 8 liter volume

3He as comagnetometer

Neutron n~29 Hz3He 3~32 Hz

Change in magnetic field due to the rotating magnetization of 3He by SQUID magnetometers

Pickup coils

Measurement cell filled with SF 4He

B

A dilute admixture of polarized 3He atoms is introduced to the bath of SF 4He (x = N3/N4 ~ 10-10 or 3He ~ 1012/cc)

3He as spin analyzer / 4He as a Detector • 3He-n reaction cross section

• 3He-UCN reaction rate

• Detect Scintillation light from the reaction products traveling in LHe– Convert EUV light to blue light using wavelength shifter– Detect the blue light with PMTs

• Signature of EDM would appear as a shift in ω3-ωn corresponding to the reversal of E with respect to B with no change in ω3

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1− p3 ⋅ pn =1− p3 pn cos (γ n − γ 3)Bt[ ] 10/3 nn =−

4He superfluid filledmeasurement cellmade of acrylic andcoated with wavelength shifter

3He + n t + p + 760 keV

J=0 = 5333 b /0 J=1 ¼ 0 nn + nn pp ppnn ppnn +pp

Critical properties of liquid helium

• 4He dispersion curve

– 8.9 Å down-scatter to UCNs by emitting phonon

• 3He spin 90% from unpaired neutron3He EDM ~0 by Schiff theorem

– effective comagnetometer

• n + 3He -> p + t + 760 keV

– spin-precession analyzer

• 4He is an effective scintillator• 4He dielectric constant – HV• 4He is a superfluid (T < 1.7 K)

– heat flush purification

nn + nnpp

ppnnpp

nn +pp

Alternative approach Dressed spin technique• By applying a strong non-resonant RF field, the

gyromagnetic ratios can be modified or “dressed”

• For a particular value of the dressing field, the neutron and 3He magnetic moments can be made equal (n’=3’)

• Can tune the dressing parameter until the relative precession is zero.

• Measure this parameter vs. direction of E

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′ =J0 γBrf /ωrf( )

B

Brf = Brf cos(ωrf t) e

Brf = 1 gauss, ωrf = 2 x 3 kHz

3He System

Volume Displacement

Purifiers

Purifier isolation Valves

3He Atomic Beam Source (ABS)

Polarized 3He

Collection System

Pressurizer

Purifier Control Valve

Collection Isolation

Valve

Pressurizer Standoff

Valve

Pressurizer Isolation

Valve

6a 6b 4

5 3

2

1a

1b

7

ABS Shutter

Measurement Cell

Measurement Cell

Cell isolation valve

T = 0 - 100 s Fill 4He with 3He

L He

3He E , B

Fill LinesT = 1100 - 1110 s /2 pulse

E , B

L Hen

3He

T = 1110 - 1610 s Precession about E & Bt

p

3He

L He

n E , B

XUV

XUV

Deuterated TPBon Walls

Light to PMT

Light to PMT

SQUID

T = 1610 - 1710 s Remove 3He

Emptying Lines

E , B

Experiment Cycle

T = 100 - 1100 s UCN from Cold n

L He

8.9 Å neutrons

Refrigerator

UCN ~ 500 Å

Phonon

(UCN)=P

E , B

SNS Fundamental Neutron Physics Beamline (FNPB)

Experiments expected to run

Cold neutron beamline

• Hadronic PV interaction• decay correlation• Neutron lifetime

UCN beamline

•Neutron EDM

Dilution Refrigerator (DR: 1 of 2)

Upper Cryostat Services Port

DR LHe Volume 450 Liters

3He Polarized Source

3He Injection Volume

Central LHe Volume (300mK, ~1000 Liters)

Re-entrant Insert for Neutron Guide

Lower Cryostat

Upper Cryostat

5.6m

4 Layer μ-metal Shield

EDM Experiment SchematicVertical Section View

Electrodes

Measurementcells

Light guides

Gain capacitor

PMTs

Lower Cryostat Cutaway View

Cold neutron beam

Magnets and Magnetic Shielding

Not shown: /2 spin-flip coil and gradient coils

B0 field direction

r = 61 cm

r = 48 cm

r = 37 cm

r = 65 cm

r = 62 cm

R&D – nearing completionActivity Name Institution

 

Neutron storage time LANL

Beamline Monte-Carlo simulation Kentucky

ABS at 45° LANL3He relaxation time Illinois

Light collection LANL

Valve development Illinois

Geometric phase effect in 3He NCState

Magnet Development Caltech

High voltage studies Indiana4He evaporative purification NCState

SQUID NMR signal Yale3He injection Duke

Laser induced fluorescence Yale

Slow Controls NCState

EDM Status & Schedule

• Approved by SNS FNPB PRAC - Fall 2005

• US DOE CD0 granted - December 2005

• R&D and design continue - 2006, 2007

• US DOE CD1 granted - February 2007

• US DOE CD2 review - late 2009

• Construction starts - 2010

• Commissioning of the experiment expected ~ 2015

Summary

• The nEDM is sensitive to new sources of CP-violation

• The SNS experiment based on new concept of measuring the nEDM directly in liquid 4He doped with polarized 3He.– uses many important properties of He which contribute

towards a ~100 x improvement in sensitivity– design sensitivity: 2 x 10-28 e cm

• The collaboration is nearing completion of various R&D phase.– CD2 review later this year– Construction to be completed ~2015