1 Electric Dipole Moment of Neutron and Neutrinos Physics of neutron EDM Status of neutron EDM...
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Transcript of 1 Electric Dipole Moment of Neutron and Neutrinos Physics of neutron EDM Status of neutron EDM...
1
Electric Dipole Moment of Neutron and Neutrinos
• Physics of neutron EDM• Status of neutron EDM measurements• Proposal for a new neutron EDM
experiment at SNS• Neutrino EDM
Jen-Chieh Peng
University of Illinois at Urbana-Champaign
Workshop on Future PRC-U.S. Cooperation in High Energy Physics, IHEP, June 11-18, 2006
2
Neutron Electric Dipole Momentexdxqn
213 10)1.14.0()(
sdxdxxd nn ˆ)( 3
Non-zero dn violates both P and T symmetry
Under a parity operation: Under a time-reversal operation:
EEss
,ˆˆ EEss
,ˆˆ
EdEd nn
EdEd nn
Consider the energy nd E
3
Physics Motivation for Neutron EDM Measurement
• Time Reversal Violation • CP Violation (in the light-quark baryon sector) • Physics Beyond the Standard Model
– Standard Model predicts dn ~ 10-31 e•cm – Super Symmetric Models predict dn ≤ 10-25 e•cm
• Baryon Asymmetry of universe – Require CP violation beyond the SM
SM Prediction Experiment
e 10-40 e•cm 10-27 e•cm
μ 10-38 e•cm 10-19 e•cm
n 10-31 e•cm 10-25 e•cm
4
SUSY Prediction of Neutron versus Electron EDM
Barbieri et al.
5
History of Neutron EDM Measurements
Current neutron EDM upper limit: < 6.3 x 10-26 e•cm (90% C.L.)
6
Neutron EDM Experiments
Limitations: • Short duration for observing the precession • Systematic error due to motional magnetic
field (v x E)
Both can be improved by using ultra-cold neutrons
Ramsey’s Separated Oscillatory Field Method
Neutron precession frequency will shift by 2 / d E
(d = 10-26 e•cm, E = 10 KV/cm => 10-7 Hz shift )
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Ultra-Cold Neutrons (UCN)• First suggested by Fermi
• Many material provides a repulsive potential of ~ 100 nev (10 -7 ev) for neutrons
• Ultra-cold neutrons (velocity < 8 m/s) can be stored in bottles (until they decay).
• Gravitational potential is ~ 10-7 ev per meter
• UCN can be produced with cold-moderator (tail of the Maxwell distribution)
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Neutron EDM Experiment with Ultra Cold Neutrons
• Use 199Hg co-magnetometer to sample the variation of B-field in the UCN storage cell
• Limited by low UCN flux of ~ 5 UCN/cm3
A much higher UCN flux can be obtained by using the “down-scattering” process in superfluid 4He
Most Recent ILL Measurement
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UCN Production in Superfluid 4He
Incident cold neutron with momentum of 0.7 A-1 (10-3 ev) can excite a phonon in 4He and become an UCN
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UCN Production in Superfluid 4He
Magnetic Trapping of UCN(Nature 403 (2000) 62)
560 ± 160 UCNs trapped per cycle (observed)
480 ± 100 UCNs trapped per cycle (predicted)
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A proposal for a new neutron EDM experiment
Collaborating institutes:
UC Berkeley, Caltech, Duke, Hahn-Meitner, Harvard, Hungarian Academy of Sciences, UIUC, ILL, Indiana,
Leiden, LANL, MIT, NIST, NCSU, UNM, ORNL, Simon-Fraser
( Based on the idea originated by R. Golub and S. Lamoreaux in 1994 )
12
How to measure the precession of UCN in the Superfluid 4He bottle?
• Add polarized 3He to the bottle• n – 3He absorption is strongly spin-dependent
Total spin σabs at v = 5m/sec
J = 0 ~ 4.8 x 106 barns
J = 1 ~ 0
KeVtpHen 7643
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Neutron EDM Measurement Cycle
• Fill cells with superfluid 4He containing polarized 3He • Produce polarized UCNs with polarized 1mev neutron beam • Flip n and 3He spin by 90o using a π/2 RF coil • Precess UCN and 3He in a uniform B field (~10mG) and a
strong E field (~50KV/cm). (ν(3He) ~ 33 Hz, ν(n) ~ 30 Hz) • Detect scintillation light from the reaction n + 3He p + t
• Empty the cells and change E field direction and repeat the measurement
33
1 1( ) { [1 cos( )]}tott
n rN t Ne P P t
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Two oscillatory signals
-15
-10
-5
0
5
10
15
603.4 603.6 603.8 604 604.2 604.4 604.6
Time (sec)
Am
plit
ud
e
3 0
33
0
3 [( ) 2 ]1) Scintillation light from with
2) SQUID signal from the precession of
/
wi ]h [ /t
He n n
He
n H B d Ee p t
He B
SQUID signal
Scintillation signal
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Status of SNS neutron EDM
• Many feasibility studies and measurements (2003-2006 R&D)
• CD-0 approval by DOE: 11/2005– Construction Possible: FY07-FY10– Cost: 15-18 M$
• CD-1 approval anticipated around 10/2006
• Collaboration prepared to begin construction in FY07
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3He Distributions in Superfluid 4He
Beam FWHM = 0.26 cm
0
5000
10000
15000
20000
25000
30000
35000
40000
-6.00 -4.00 -2.00 0.00 2.00 4.00 6.00
Position (cm)
n-3
He
No
rma
lize
d C
ou
nts
Neutron Beam
Position
4He
TargetCell
3He
Preliminary
T = 330 mK
Dilution Refrigerator atLANSCE Flight Path 11a
Physica B329-333, 236 (2003)
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Neutron Tomography of Impurity-Seeded Superfluid Helium
Phys. Rev. Lett. 93, 105302 (2004)
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Critical dressing of neutrons and 3HeDress field can modify
neutron and 3He g factors:
3neutron
He
3 1n 1n 0 3 0
0 0
c c
g g
BBg J g J
J x J x
1.1127
3Heneutron
B1
1.19 0.408
3.86 1.324
6.77 3.333
9.72 4.348
cx
n 1 /x B
Effective dressed g factors:
Reduce the error caused by B0 instability between
measurements
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Los Alamos Polarized 3He Source
1 K cold head
Injection nozzle
Polarizerquadrupole
Spin flip region
Analyzerquadrupole
3He RGAdetector
B1 dressing
B0 static
Polarizer Analyzer RGA
36 in
3He Spin dressing experiment
Ramsey coils
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Observation of 3He dressed-spin effect
3He Larmor Frequency
26.2
26.4
26.6
26.8
27.0
27.2
27.4
27.6
0 2 4 6 8 10
Dressing Coil Current [A]
3He
Larm
or F
requ
ency
[k
Hz]
Esler, Peng and Lamoreaux (2006)
21
22
Polarized 3He relaxation time measurements
H. Gao, R. McKeown, et al, arXiv:Physics/0603176
T1 > 3000 seconds in 1.9K superfluid
4He
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UIUC Test Apparatus for Polarized 3He Relaxation at 600 mK
Work carried out by UIUC and students from Hong Kong
(CUHK)
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SNS at ORNL1.4 MW Spallation Source1.4 MW Spallation Source
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n EDM Experiment at SNS
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n-EDM Sensitivity vs Time
2000 2010
dn<1x10-28 e-cm
EDM @ SNSEDM @ SNS
27
Neutrino electric dipole moment • For Majorana neutrinos, CPT invariance ensures zero electric
and magnetic dipole moments• For Dirac neutrinos, non-zero EDM is possible (CP-violation)
17
21
20
2 22 2
2
Bounds on neutrino EDM ( )
1 / (| |
| | 5.2 10
| |
From
|
2 10 (MUNU, TEXONO)
| | 1.4 10 (LSND)
| | 7.8
width
From -e scattering
| )
e
d
e
T Edd
dT m
d e cm
d e cm
d e c
d
T
m
18
22
10 (DONUT)
| | 2.5 10 (PL 128B (1983) 43
From cosmo g
1)
lo y
e cm
d e cm
Another dedicated neutrino experiment is required at Daya Bay to improve the sensitivity on the neutrino EDM
28
Summary• Neutron EDM measurement addresses
fundamental questions in physics (CP violation in light-quark baryons).
• A new neutron EDM experiment uses UCN production in superfluid helium and polarized 3He as co-magnetometer and analyser.
• The goal of the proposed measurement is to improve the current neutron EDM sensitivity by two orders of magnitude.
• Many feasibility studies have been carried out. Construction is expected to start in FY2007.