A New Search on the Neutron Electric Dipole Moment (nEDM)

2008 Fall Chinese Physical Society Meeting September 20, 2008

Jinan, China

Haiyan Gao (高海燕 ) Duke University

Outline

• Introduction

• Existing measurements

• A new search for neutron EDM

• Summary

Introduction• P – Parity (Space Inversion)

• T – Time Reversal

• C – Charge Conjugation Particle Anti-particle

• Parity violation– Theory - 1956, Lee & Yang[1]

– Experiments in 1957• Wu et al. 60Co β-decay[2]

• Garwin et al. πμe[3]

• Friedman & Telegdi et al.[4]

r r

t t

[1] T. D. Lee and C. N. Yang. Physical Review, 104:254, 1956.[2] C. S. Wu et al. Physical Review, 105:1413, 1957.[3] R. L. Garwin et al. Physical Review, 105:1415, 1957.[4] J. I. Friedman and V. L. Telegdi. Physical Review, 105:1681, 1957.

CP Violation in weak interactions

In 1964, Christenson, Cronin, Fitch and Turlay discovered at BNL that the long-lived neutral K meson with CP=-1 could decay occasionally to with CP=+1 about once every 500 decays

K oL o

K oL

• CP violations in nuclear systems• More CP violations in experiments: B meson decays, SLAC and KEKFuture experiments studying CP in neutrino sector

CP=-1 CP=+1 0.2%

CP violation in Standard Model

• The CKM matrix: the complex phase of CKM matrix leads to CP violation

d '

s'

b'

Vud Vus Vub

Vcd Vcs Vcb

Vtd Vts Vtb

d

s

b

ˆ V CKM

d

s

b

For n generations:n(n-1)/2 angles 3(n-1)(n-2)/2 phases 1

Weak eigenstates

Mass eigenstates

•To lowest order, CP violation occurs only in flavor-changing processes.

Strong CP problem•The θ term in QCD lagrangian

• If θ≠0, violates P & T

• Neutron EDM ~ O(10-16 θ) e.cm[1,2,3]

– Current nEDM upper limit 2.9×10-26 e.cm[4]

2

23[ ]

2

1

4QCD n n nn

L G G i g G Tg

G Gm

[1] Maxim Pospelov and Adam Ritz. Phys. Rev. Lett., 83, 2526 (1999)[2] V. Baluni. Phys. Rev. D 19, 2227 (1979)[3] R. J. Crewther et al. Phys. Lett. B 88, 123 (1979)[4] C.A. Baker et al. Phys. Rev. Lett. 97, 131801 ( 2006)

G G

1010

1

2G G

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

CPT Invariance

CPT is a good symmetry in a local field theory which is Lorentz invariant and has a hermitian Lagrangian– CP violation thus implies time-reversal

symmetry T violation– Direct search for T violation is important!

• CPLEAR: semi-leptonic decay of neutral kaons• KTev experiment • Neutron electric dipole moment (nEDM)

KL ee

Neutron Electric Dipole Moment (EDM)

• If neutron possesses EDM, in an electric field, Hamiltonian – changes sign under T (P) symmetry

operation

• is more sensitive to than it is to

H dn

E

dn

CKM

+-

s = 1/2d•E

Quark EDM appears only at the three-loop level

Predictions for Neutron EDM

• SM: – Renormalization of QCD vacuum parameter arising from

CP violation in weak interaction (CKM)

– Strong CP: (m)2ln (m)2 ,……

• Left-right symmetric gauge models:

• Non-minimal Higgs models:– CP odd gluonic operators inducing:

• Supersymmetry (SUSY) models

dn 10 31ecm

dn 10 27ecm

dn 10 27ecm

B-B ASYMMETRY IN THE UNIVERSE

Before PhaseTransition

After PhaseTransition

Today

N

0

1010

BB BB BB

10 10N

N B

1

NN

NNA

BB

BBBB10 10

2

1

0

2

1

CP Violation and Cosmology

• Baryon asymmetry of the universe (BAU)•

• To explain BAU, substantial New Physics in the CP violating sector is required

• Neutron EDM may play an important role in quantifying New Physics

• New source of CP beyond SM may have significant impact on our understanding of baryongenesis

nbar( today )

n

(4 7) 10 10

nbar

n

Seminar paper by A. Sakharov (1967) on calculating BAU

Existing Measurements of

Experimental techniques:– Neutron scattering

• Interference between neutron-nucleus and neutron-electron

– Magnetic resonance technique • thermal or cold neutron beams

• bottled ultra-cold neutrons (UCN)

dn

Ref: R. Golub and S. K. Lamoreaux, Phys. Report 237, 1-62 (1994)

+-

E

s = 1/2 dipole moment dn

Look for a precessionfrequency dB

Magnetic Resonance Technique

•A strong static electric field applied parallel (anti-parallel) to the magnetic field causes a shift in the Larmor freq.

)2/(/]22[ 000 hEdB nnn

hEdn /4 0

Frequency Measurement

• Neutron spin aligned perpendicular to a static magnetic field

• The frequency shifts as the direction of E is reversed is from parallel to

B to antiparallel to B:

4dn Eo /h

B0 10mG

E0 0

0 29.2Hz

E0 50kV /cm

dn 4 10 27ecm

0.19Hz 0.66 10 8 0

(*It takes two months to make a 2 rotation.)

Permanent magnet

PolarizerAnalyzer

Magnetic fieldElectric fieldNeutron spin

DetectorNeutron beam

Electrodes

First nEDM experiment at ORNLJ.H.Smith, E.M.Purcell, and N.F.Ramsey, Phys. Rev. 108, 120 (1957)

Neutron electric dipole moment

• nEDM more sensitive to θQCD than to δCKM[1]

[1] Jiang Liu, C. Q. Geng, and John N. Ngl. Phys. Rev. Lett., 63:589, 1989.[2] E. M. Purcell and N. F. Ramsey. Phys. Rev., 78:807, 1950.[3] C.A. Baker et al. Phys. Rev. Lett., 97:131801, 2006.[4] B. McKellar et al., Phys. Lett. B, 197:556, 1987.

Current upperlimit

(ILL)[3]

New Physics!!!New sources of CP violation?

[4]

Projected result in

2014

(n beam)

Name Velocity

thermal ~2200 m/s

Cold 98-2200 m/s

Very cold 7.6-98 m/s

Ultra cold <7.6 m/s

1950, Smith, Purcell

and Ramsey[2]

Experimental limits on the particle EDM

Current best limit on neutron EDM is from ILL reactor atGrenoble Phys. Rev. Lett. 97, 131801 (2006)

< ecm [90 % C.L.]

3.0 10 26nEDM

A new nEDM Experiment(Spokespersons: S. K. Lamoreaux, M. Cooper)

NE175

Figure of Merit for EDM Experiments ~

E 5E 5 N 250 N Compared to ILL experiment

Overview of the Experiment

– A three-component fluid of ultra cold neutrons,3He atoms in a bath of superfluid 4He at ~400 mK

– Neutron and 3He magnetic dipoles precess in a plane perpendicular to the external magnetic field

– Precision measurement of the freq.difference in the 3He and neutron precession frequency modified when strong E field is turned on (or reversed) --> neutron EDM

Production of Ultracold Polarized Neutrons

• Closed neutron trap filled with ultra-pure superfluid 4He cooled to ~ 350 mK

• Placed in a beam of cold neutron (E=1 meV), polarized (~100%) using two total reflecting magnetic supermirror surfaces

• Neutrons interacting with the superfluid are downscattered to with a recoil phonon in the superfluid carrying away the missing energy and momentum (Golub, Pendelbury, 1975)

• Technique has been demonstrated at a number of laboratories (France, Japan, US)

E 0.13eV ,V 5m /s

Superthermal process to produce UCNs

• Cold neutron polarized by “supermirror”[1]

• “Superthermal” process

• Neutrons with energy ~0.001eV (λ=8.9Å, v=446m/s) can scatter into UCNs (v<7 m/s) by emitting a phonon[2].

[1] The nEDM Collaboration. Conceptual Design Report for the nEDM Project, 2007.[2] R. Golub, D. J. Richardson, and S. K. Lamoreaux. Ultra-Cold Neutrons. Adam Hilger, Bristol, 1991.

Upscattering process suppressed by a factor

*/E Te

Superfluid 4He elementary excitation dispersion curve

Measurement Principle - UCN with Polarized 3He in superfluid 4He

• Experimental cell Rectangular, made of acrylic coated with d-TPB

(Deuterated tetraphenyl butadiene)

• Three-component fluid

~ 150 /n cc 113 ~ 8 10 /He cc

x

y

z

B E

UCN, 3He, 4He

Polarized cold neutron beam(E = 1 meV, v = 440 m/s, l = 8.9 Å)

B~10mGE~50kV/cm

Superthermal process to produceUCN. E<0.13µeV, v<7 m/s

Superfluid 4He at~300-500 mK

Polarized 3He

How to measure the UCN Precession Frequency?

In the trap volume:

atoms per liter of cell volume

NUCN 1.2 106,

N 3 He 1.6 1016,

N 4 He 1.76 1026

?

•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

Measurement of the UCN Precession Frequency

• UCN precession frequency beat against the 3He precession frequency

• Spin dependence of the nuclear interaction cross-section:

• Scintillation light from nuclear reaction products (and beta decay products) (80 nm) can be wave-length shifted (440 nm) and detected

n 3

H e p t 772keV

Spin State Cross Section

(barns)

(v=2200 m/sec)

Cross Section

(barns)

(v=5 m/sec)

J=0

J=1

~ 1.1104

~ 4.8 106

~0

~ 0

n 3He p t 772keV

dn dipole moment d3 =0

Look for a difference in precessionfrequency n - 3 d dependent on Eand corrected for temporal changes in 3

+-

EB EB

s = 1/2

n 3He

3He MAGNETOMETRY

L.I. Schiff, Phys. Rev. 132, 2194 (1963)

UCN Precession Frequency

The time dependent, velocity independent loss rate

SQUID will be used for monitoring the 3He spin precessionFrequency, 3He also a co-magnetometer

]]}2)cos[()()(1[1

1{)(

333

EtdBttPtP

Net

nnHenHeHe

tbg

Systematic Error

• effect (UCN)

• B field fluctuation (Comagnetometer)

• Accuracy of flipping the E field

• Gravitational offset[1]

• Geometric phase effect[2]

• ……

Error analysis Statistical Error

• nEDM uncertainty• Uncertainty principle

• Higher UCN density higher sensitivity

• Measure nEDM or lower the current upper limit by ~2 orders of magnitude

04n

nd hE

0

/ 4n

m

d e cmE T Nm

2810nd e cm

v E

[1] I. B. Khriplovich and S. K. Lamoreaux. CP Violation Without Strangeness. Springer, page 93, 1997.[2] J. M. Pendlebury et al. Phys. Rev. A, 70(3):032102, Sep 2004.

E0=50 kV/cmTm=500 sN=106 n/cyclem=6000 cycles

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

Spallation Neutron Source (SNS) at ORNL

January 25, 2005

1 GeV, 1.4 mA Proton Linac

•SNS completed: 2006•FNPB Beam line completed: 2007•Full design flux: 2008•SNS Total Project Cost: 1.411B$

SNS Target Hall

SNS

IDT

1B - Disordered Mat’lsCommission 2010

2 - Backscattering Spectrometer Commission 2006

3 - High Pressure Diffractometer Commission 2008

4A - Magnetism Reflectometer Commission 2006

4B - Liquids ReflectometerCommission 2006

5 - Cold Neutron Chopper Spectrometer Commission 2007

18 - Wide Angle Chopper Spectrometer Commission 2007

17 - High Resolution Chopper SpectrometerCommission 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

Summary

CD-2 review 08

This work is supported by the US Department of EnergyDE-FG02-03ER41231 and School of Arts and Science at DukeThanks to Qiang Ye for the preparation of a few nice slides

CD-1 Feb 2007

PRL 97, 131801

Projected result ~ 2014

OCPA6 Conference August 3-7, 2009 in Lanzhou, China.Hosts: IMP and Lanzhou Univ.Conference web page: http://snst.lzu.edu.cn/web1/index.htmlPlease visit OCPA web page:www.ocpaweb.orgWe invite you to become a member!

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Achievement in Asia Award (Robert T. Poe Prize)