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A New Search on the Neutron Electric Dipole Moment (nEDM) 2008 Fall Chinese Physical Society Meeti September 20, 2008 Jinan, China Haiyan Gao ( 高高高 ) Duke University
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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 )

Dec 13, 2015

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Page 1: 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 )

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

Page 2: 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 )

Outline

• Introduction

• Existing measurements

• A new search for neutron EDM

• Summary

Page 3: 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 )

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.

Page 4: 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 )

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%

Page 5: 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 )

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.

Page 6: 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 )

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.

Page 7: 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 )

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

Page 8: 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 )

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

Page 9: 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 )

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

Page 10: 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 )

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

Page 11: 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 )

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

Page 12: 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 )

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)

Page 13: 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 )

+-

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

Page 14: 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 )

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.)

Page 15: 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 )

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)

Page 16: 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 )

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]

Page 17: 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 )

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

Page 18: 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 )

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

Page 19: 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 )

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

Page 20: 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 )

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

Page 21: 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 )

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

Page 22: 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 )

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

Page 23: 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 )

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

Page 24: 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 )

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

Page 25: 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 )

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

Page 26: 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 )

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)

Page 27: 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 )

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

Page 28: 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 )

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

Page 29: 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 )

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

Page 30: 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 )

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$

Page 31: 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 )

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

Page 32: 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 )

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

Page 33: 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 )

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!

http://www.ocpaweb.org/new/aaaaward/aaaaward.html

Achievement in Asia Award (Robert T. Poe Prize)