The nEDM Experiment at the SNS

Christopher CrawfordUniversity of Kentucky

for the nEDM Collaboration

77th Annual Meeting of the

Southeastern Section of the APS,

Baton Rouge, LA 2010-10-23

Outline

• Introduction to neutron physics and the SNS• EDM properties – scientific motivation• Separated oscillatory fields – ILL experiment• Properties of He – new technique• Experimental setup – expected results

2

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

Radial charge distribution – data including BLAST3

Cold and Ultra-Cold Neutrons (UCN)

3mg

• Cold neutrons: λ ~ 2 – 20 Å glancing reflections along guides

• UCN 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)

4

n p

d

γp (or d)

d (or t)

n γ

What can we do with neutrons?

• Scattering / Bragg diffraction– Complementary to X-ray diffraction

• Neutron interferometry• Fundamental symmetry tests

of the standard model– Neutron decay lifetime and correlations– PV: NPDGamma, 4He spin rotation– T reversal: electric dipole moment

Electron

Proton

Neutrino

Neutron SpinA

B

C

nEDM

5

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

6

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

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

Spallation Neutron Source (SNS)

7

1B - Disordered Mat’lsCommission 2010

2 - Backscattering Spectrometer

Commission 2006

3 - High Pressure Diffractometer

Commission 2008

4A - Magnetism Reflectometer

Commission 2006

4B - Liquids Reflectometer

Commission 2006

5 - Cold Neutron Chopper

Spectrometer Commission 2007

18 - Wide Angle Chopper Spectrometer

Commission 2007

17 - High Resolution Chopper Spectrometer

Commission 2008

13 - Fundamental Physics Beamline Commission 2007

11A - Powder Diffractometer

Commission 2007

12 - Single Crystal Diffractometer

Commission 2009

7 - Engineering Diffractometer IDT CFI Funded

Commission 2008

6 - SANS Commission 2007

14B - Hybrid Spectrometer

Commission 2011

15 – Spin Echo

9 – VISION

Beamline 13 allocated for nuclear physics

8

SNS Fundamental Neutron Physics Beamline (FNPB)

Experiments expected to run

Cold neutron beamline

• Hadronic PV interaction• decay correlation• Neutron lifetime

UCN beamline

•Neutron EDM

9

Cold Neutron Beamline – NPDGamma expt.

10

FnPB neutron flux vs. MC simulation

~ λ-5

shifted slightly toward longer wavelengths

2.1 x 1011 neutrons/sat full power (1.4 MW)

11

Electric Dipole Moment

• 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))

+

-P reversal

+

-

+

-T reversal

12

Evolution of EDM Experiments

J.M. Pendlebury and E.A. Hinds, NIM A 440, 471 (2000)

13

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’

γ

W W

e+i e-i

Standard Model€

˜ f

€

˜ f

€

˜ γ €

γ

€

fL

€

fR

€

e+iφL

€

e−iφ R

SUSY

14

• 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

€

np /np ~ 10−4

€

NB

Nγ

=N

B

Nγ

~ 10−18 (kTcritical ≈ 20 MeV)

€

NB

Nγ

≈10−9

Baryon Asymmetry of the Universe

15

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.

€

Lθ = θgs

2

32π 2˜ G μν Gμν

€

dn ~ O 10−16θ( ) e ⋅cm

€

θ <10−9 Strong CP problem

16

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

17

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)

19

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, Grenoble, France• Selected parameters:

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

• Results– dn< 2.8x10-26 ecm (90%CL)

20

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

21

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

€

Br =r

2

∂BZ

∂z= arRadial gradient

Bv = v x E field changes sign with direction

€

ω =−γ2av 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

22

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)23

•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 volume24

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)

25

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

€

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

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

26

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

27

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 (γn’=γ3’)

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

• Measure this parameter vs. direction of E

€

′ γ =γJ0 γBrf /ωrf( )

B

Brf = Brf cos(ωrf t) e

Brf = 1 gauss, ωrf = 2 x 3 kHz

28

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

29

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 γ

XUV γ

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

30

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

31

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

32

Electrodes

Measurementcells

Light guides

Gain capacitor

PMTs

Lower Cryostat Cutaway View

Cold neutron beam 33

Application: new method of designing magnetic coils (from the inside out)

• Standard iterative method:Create coils and simulate field.

• New technique: start with boundary conditions of the desired B-field, and calculate the winding configuration

1. Use scalar magnetic potential (currents only on boundaries)

2. Simulate intermediate region using FEA with Neumann boundary conditions (Hn)

3. Windings are traced along evenly spaced equipotential lines along the boundary

red - transverse field linesblue - end-cap windings

Magnetostatic calculation with COMSOL

34

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 35

Summary

• The nEDM is sensitive to new sources of CP-violation– Physics beyond the standard model– To explain the Baryon Asymmetry in the Universe

• The SNS experiment based on new concept of measuring the nEDM directly in liquid 4He doped with polarized 3He.– Systematic sensitivity: 3 x 10-28 e cm (limited by geometric phase)

– Statistical sensitivity: 8 x 10-28 e cm (prospect of 4.5 x higher flux)

• The collaboration is nearing completion of R&D.– CD2 review early next year– Begin operation ~2017

36

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

37