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
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!
http://www.ocpaweb.org/new/aaaaward/aaaaward.html
Achievement in Asia Award (Robert T. Poe Prize)