Neutron
Electric
Dipole
Moment
By: Christopher Hayes
Physics 564
12/01/2007
Properties of the Neutron
Mn=939.565MeV
Tn=885.7 s
 = n• N • Sn
sn
u
d
d n
d
dn< 2.9x10-26 e·cm
2
Symmetry Operations
u
d
d
T[dn]= dn
T[sn]= -sn
P[dn]= -dn
P[sn]= sn
u
d
d
d
d
u
3
Consequences of a Non-Zero nEDM

First direct observation of T-violation

Second observation of CP violation

Evidence that the Strong Force does not
conserve parity

A new clue to the origin of the baryon
asymmetry of the universe
4
nEDM and Extensions of the SM
Theory
EDM Prediction
Supersymmetry (SUSY)
~10-27 e·cm
Additional Higgs fields
~10-26 e·cm
Left-Right Symmetric
Models
~10-25 e·cm
CP in QCD
LQCD ~ L0 + ι ·gs2·GG
~10-26 e·cm
Standard Model (SM)
~10-31 e·cm
5
nEDM Measurement Principle
h1= 2n• B + 2dn • E
z
B, E
h2= 2n• B - 2dn • E
h  = h (2- 1)
y
= 4dn • E
dn = h /4E
x
dn
n
6
Experiment to Measure nEDM
B = 10-3 Gauss
E = 10kV/cm
Larmor~ 30 Hz
N ~ 15,000
Vbottle ~ 20 liters
Cycle ~ 200 s
7
Measured Precession Frequencies
Superimposed on Alternating E-field
8
Ultra Cold Neutrons (UCN’s)

UCN Energies…………..En ~ 0.2eV

UCN Speeds…………….Vn ~ 6 m/s

UCN Wavelengths………n ~ 60nm


Only UCN neutrons are capable of total internal
reflection
Transport pipes and EDM storage cell operate on
the principle of Total Internal Reflection
9
Production of UCN’s
Nuclear
Reactor
or
Spallation
in High Z
targets
E ~ 2 MeV
Moderator
(Heavy
water)
UCN
Turbine
E ~ .2 eV
E ~ 2 meV
10
Results of EDM experiments



First EDM test result in 1950:
dn ~ 10-18 e•cm
Current upper limit measured at ILL:
dn< 2.9 x 10-26 e•cm
Next generation experiments:
dn< 10-28 e•cm
11
How to Improve Results


Increase Electric field Strength
dn ~ E
Increase neutron density
d ~ [a·E·T ·(N)1/2]-1


Increase storage times
Increase polarization efficiency
12
Research Facilities




Institut Laue-Langevin (ILL): Grenoble,
France
Petersburg Nuclear Physics Institute
(PNPI): Gatchina, Russia
Paul Scherrer Institute (PSI): Villigen
Switzerland
Los Alamos National Laboratory
(LANL)/Los Alamos Neutron Science
Center (LANCE)
13
EDM for other particles

Can measure EDMs for protons,
electrons, muons, and other
particles
de= .07 x 10-26 e•cm
d = 3.7 x 10-19 e•cm
dp< .54 x 10-23 e•cm
14