n
Measurement of the Neutron
Spin-Rotation in Solid
Orthodeuterium
Diane Markoff
North Carolina Central University (NCCU)
Triangle Universities Nuclear Laboratory (TUNL)
INT – June 07
Weak Hadronic Interaction
Weak Coupling ~ (10-6) Strong Coupling
Isolate the weak hadronic interaction through
the violation of symmetry.
FLAVOR VIOLATION (quark type; strangeness or charm changing)
  p  
High-Energy Regime: Weak decays
PARITY VIOLATION


; K     0

(spatial inversion; r  r )
Low-Energy Regime:
s  p 
interactions
Study flavor conserving, parity-violating interactions
accessible only in the Nucleon-Nucleon system.
Characterize the hadronic weak interaction

Weak NN Theoretical Descriptions
Meson exchange model for weak NN
[effect of qq weak interactions parameterized by ~6 couplings]
f, hr0, hr1, hr2, hw0,hw1 (DDH Annals of Phys 124(2)449-95,1980)
Pionless Effective Field Theory
model independent and consistent with cPT
5 low-energy constants associated with S-P transition amplitudes
rt [3S1 (I=0) ↔ 3P1 (I=1)]; lt [3S1 (I=0) ↔ 1P1 (I=0)];
ls0,1,2 [1S0 (I=1) ↔ 3P0 (I=1) DI = 0,1,2] (lspp, lspn, lsnn)
EFT with Pions – two more independent parameters
Example of Coupling Constant Data
One Set of Proposed Measurements
Longitudinal analyzing power AL in pp and p scattering
Circular polarization P and photon asymmetry A in
radiative neutron capture (np→d)
Spin rotation , of polarized neutrons through helium

mN l pp  1.22 AL ( pp)

mN rt  9.35 A (np  d )




mN l pn  1.6 AL ( pp)  3.7 AL ( p )  37 A (np  d )  2 P (np  d )




mN lt  0.4 AL ( pp)  0.7 AL ( p )  7 A (np  d )  P (np  d )





mN lnn  0.83 (n )  0.69 AL ( pp)  1.18 AL ( p )  33.3 A (np  d )  1.08 P (np  d )
Report to NSAC Submitted by the
subcommittee on Fundamental Physics
with Neutrons August 2003
EFT Coupling Constants
rt
lt
ls 0 ls 1
ls 2
AL(pp)
AL(p)
P(np)
A(np)
(n)
And
S.G. Page and M. Ramsey-Musolf, Ann. Rev. Nucl. Part. Sci. 56 (2006)
Neutron Spin Rotation
n
In 1964, Michel first proposed that the weak
interaction could produce an observable effect
with neutrons that is analogous to the observed
optical rotation of polarized photons propagating
through a handed medium.
 PNC      2PNC  4rl f PNC
f PNC 
 mn
2
Re
4
He, i H wk  0 , 4 He
(Michel, PhysRev 1964)
(Dmitriev et al., PhysLettB 1983)
As a result of the PV weak interaction, positive and negative helicity
neutrons travel through a medium with different effective indices of
refraction. We observe the resulting phase difference between helicity
states as a rotation of the transverse spin polarization vector about the
momentum direction by an amount proportional to the weak interaction
matrix element.
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Neutron Spin Rotation
in Few-Body Systems
n) liquid helium
calculations have been done
initial measurement – large errors
(n,) = (8 ± 14 (stat) ± 2 (sys)) 10-7 rad/m
currently at NIST
nDorthodeuterium
no calculations yet
proposed measurement for NIST
(np) parahydrogen
calculations have been done
proposed measurement for SNS
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Basic Design for Spin-rotation
PNC= 4rlfPNC
• Long-wavelength, cold-neutrons (l > 1 Å)
• High-density, liquid/solid target (LHe, LH2, D2)
• Reduce effects from background (PC) rotations
MAG ~ 10 radians for B = 0.5 Gauss
 magnetic shielding (Baxial < 100 mG)
• Extract small spin-rotation signals
 two targets with a -coil to modulate the signal
 detect n with velocity separation and geometry separation
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Simultaneous Signal Modulation
BKG  PNC
BKG + PNC
3He
n-detectors
Analyzer
PNC
PNC
•
Target Chamber
Back Position
 - Coil
Target Chamber
Front Position
PNC
•
Cold Neutron Beam
Polarizer
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Spin-Rotation Measurement
IDEAL POLARIMETER
REAL POLARIMETER
N  N
sin  
N  N
1 N  N
sin  
P N  N
P is the measured polarization
product of the polarimeter
Low Energy n Scattering in D
n
D2
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What is the extent of
depolarization of the
neutron transmitted
through an
orthodeuterium target?
Ortho – D2 : Symmetric spin configuration S=0 (ground state), S=2
neutron spin flip allowed for all neutron energies
(ortho-D2 primarily S=0 for cryogenic temperatures)
scatt~2 barns, ~0.001 barn
Note: Para – D2 antisymmetric spin state, S=1,3,5…
Measurement of Cold Neutron
Depolarization in Liquid and Solid
Deuterium
A. Komives, A. Bever, S. Carlson
DePauw University
W. M. Snow, Y. Shin, C.Y. Liu
Indiana University
J. Dawson
University of New Hampshire
K. Kirch, M. Kasprzak, M. Kuzniak, B. Van den Brandt, P. Hautle,
T. Konter, A. Pichlmaier
Paul Scherrer Institute
K. Bodek, S. Kistryn, J. Zejma
Institute of Physics; Jagiellonian University
Setup for Measurement
Side View
polarizer Flipper 1 chopper
Polarization
analyzer
D2 target
1
P+
q
N0
P-
2
Flipper 2 detector
4 cm Solid/Liquid 98% Ortho-D2
20 K (Liquid)
18 K (Solid)
Flippers/chopper/analyzer/detector used in FUNSPIN beam
characterization (NIM, 2005)
Deuterium Target
Diameter of nearly fully grown crystal: 3.8 cm
Neutron Depolarization
PRELIMINARY
Neutron Polarization
PRELIMINARY
Neutron Polarization – Normalized
To the Empty Target Cell Values
Conclusions
• ~ 5% depolarization observed for cold
neutrons in solid orthodeuterium
• ~ 15% depolarization in liquid orthodeuterium
• Use solid orthodeuterium target
– Depolarization not as much of a problem as once
thought for deuterium targets
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Spin-Rotation Measurement
IDEAL POLARIMETER
REAL POLARIMETER
N  N
sin  
N  N
1 N  N
sin  
P N  N
P is the measured polarization
product of the polarimeter
n Schematic of n-Spin Experiment
NIST Spectrum
NG-6 beam line at NIST (Gaithersburg, MD)
9.E+07
•
energies in the 10-3 eV range (l ~ 5Ǻ)
•
bismuth filters
provide high-energy cut-off
Neutron Flux (1996)
8.E+07
– Choose thickness to remove l< 6Ǻ
(Bragg peak for ortho-D2 at 2meV, 6Ǻ.)
Flux ( n/cm^2/s )
7.E+07
6.E+07
•
5.E+07
Low-energy neutron filter
– Høghøj et al. NIM in PhysResB 160 (2000)
– Remove long wavelength neutrons
4.E+07
3.E+07
2.E+07
1.E+07
0.E+00
0
1
2
3
4
5
6
7
8
9
10
wavelength ( angstroms )
11
12
13
14
15
NG-6 Spectrum 2005
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Sensitivity Estimate
• n- neutron fluence in polarizing and transport
assembly (no target) ~ 5  107 n/cm2-sec (two parallel
beams of 5 cm  2.5 cm)
• About half of measured neutrons in spectrum at the
detector is above 6 Ǻ.
• Choose D2 target 2 mean-free path lengths
~ 2 barns/atom for solid ortho-D2 at 18 K below Bragg cutoff at 2 meV therefore use 16 cm targets
• Increase transmission with improved input guides
• Likely have thicker windows for safety with increased
beam losses through the target region
• Polarization losses (20%) in the target
Sensitivity Estimate (continued)
• Statistical contribution (ignore error in P)
 sin  P1
1
N
• Statistical sensitivity: 10-7 radians for 1
month data in a 16 cm target
(3  10-7 rad/m in 4 months of data)
Note: y(1-2)  10-6 rad/m for spin rotation in
few body systems
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General Systematics
The cancellation of background rotations is limited by
the apparatus being the "same" for both target states.
• Target dependent neutron scattering
beam divergence and velocity changes for liquid
vs. "empty" target (reflection off surfaces, target
length changes, effective index of refraction)
• Magnetic field induced rotations (B<100mG)
change in rotation for change in local fields
(diamagnetism of target, neutron travel time in
the target region)
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D2 Systematics
• Diamagnetism of deuterium
DB/B = 5  10-6 : for l=7Ǻ, mag= 0.7 mrad in 100mG field giving ~ 3  10-9 rad
change in spin rotation from magnetic susceptibility
• Deuterium material slows the n beam
for 6 Ǻ neutron, Dv ~ 2  10-5. In 100mG field, the change in spin rotation is ~ 10-7.
For these two effects, uniformity of the magnetic fields can reduce the effect by
a factor of 10.
• Target length difference coupled to shift in n scattering
Weak but non-negligible energy dependence of n-D scattering causing velocity shift
of n beam after passing through the target D increasing for longer target –
coupled to a residual field gives a systematic effect.
Dv/v ~ 1 %, in a 100mG field and DL/L = 0.01 cm for the two targets gives a 2  10-9
effect
• Small angle scattering in the target coupled to time in B field
Estimate fraction of detected small angle scattered neutrons with fractional change
in time these neutrons spend in the field gives a 3  10-8 difference in rotation
Monitor velocity dependent systematic effects.
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What We Have Done Before
Segmented Ionization
Chamber Detector for n-4He
ORIGINAL DESIGN
Ionization Chamber
n + 3He → p + t
Collect charged proton and triton
on charge collection plates.
Divide charge collection plates
into 4 quadrants (3" diam)
separated L/R and U/D beam
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What We Have Done Before
Segmented Ionization
Chamber Detector for n-4He
ORIGINAL DESIGN
Ionization Chamber
3He and Ar gas mixture
4 Detection Regions
along beam axis
velocity separation
(1/v absorption)
Gas pressure so that
transverse range
of the proton < 0.3 cm
Note region size increases for approximately equal
count rates: 30% of beam in regions 1, 2, 3+4
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What We Have Done Before
Segmented Ionization
Chamber Detector for n-4He
Penn et al. NIM 457, 332 (2001)
0.5 atm 3He, 3 atm Ar gas mixture
4 detection regions along axis
4 quadrants per region
 16 channels with coarse position
sensitivity and large energy bins
Count rate: 107 n/sec – current mode
~ 7×105 n/sec/channel
(1996 digital picture shows
4-region, quadrant detector)
(Allows measurement of rotations
from magnetic fields ~ 40 mG)
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Proposed n-D Spin Rotation
Experiment
• Use polarimeter apparatus from current n-
experiment at NIST
• Design D2 target system and cryostat
– Gas handling and safety system for ~ 1.5 liters solid
ortho-D2
– Para-ortho conversion catalyst
– Move 3-region target chamber sideways for target in
and dummy target in beam position
• Schedule data runs in 2010
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Summary
• n-D spin rotation is a feasible measurement
• Looking toward success of n- measurement
• Calculation needed to place (nD) observable
into perspective to determine its contribution to
the scheme of specifying the weak hadronic
coupling constants