Measurement of the Neutron Spin-Rotation in

Solid Orthodeuterium

Diane Markoff

North Carolina Central University (NCCU)

Triangle Universities Nuclear Laboratory (TUNL)

nnn

INT – June 07

Weak Hadronic Interaction

FLAVOR VIOLATION (quark type; strangeness or charm changing)

High-Energy Regime: Weak decays

PARITY VIOLATION (spatial inversion; )

Low-Energy Regime: interactions ps

0; Kp

rr

Weak Coupling ~ (10-6) Strong CouplingIsolate the weak hadronic interaction through

the violation of symmetry.

Characterize the hadronic weak interaction

Study flavor conserving, parity-violating interactionsaccessible only in the Nucleon-Nucleon system.

Meson exchange model for weak NN [effect of qq weak interactions parameterized by ~6 couplings]f, h

0, h1, h

2, h0,h

1 (DDH Annals of Phys 124(2)449-95,1980)

Pionless Effective Field Theorymodel independent and consistent with PT5 low-energy constants associated with S-P transition amplitudest [3S1 (I=0) ↔ 3P1 (I=1)]; t [3S1 (I=0) ↔ 1P1 (I=0)]; s

0,1,2 [1S0 (I=1) ↔ 3P0 (I=1) I = 0,1,2] (spp, s

pn, snn)

EFT with Pions – two more independent parameters

Weak NN Theoretical Descriptions

Example of Coupling Constant Data

One Set of Proposed Measurements

)(08.1)(3.33)(18.1)(69.0)(83.0

)()(7)(7.0)(4.0

)(2)(37)(7.3)(6.1

)(35.9

)(22.1

dpnPdpnApAppAnm

dpnPdpnApAppAm

dpnPdpnApAppAm

dpnAm

ppAm

LLnn

N

LLtN

LLpn

N

tN

Lpp

N

Longitudinal analyzing power AL in pp and p scatteringCircular polarization P and photon asymmetry A in

radiative neutron capture (np→d)Spin rotation , of polarized neutrons through helium

Report to NSAC Submitted by thesubcommittee on Fundamental Physics with Neutrons August 2003

EFT Coupling Constants

S.G. Page and M. Ramsey-Musolf, Ann. Rev. Nucl. Part. Sci. 56 (2006)

AL(pp)

AL(p)P(np)A(np)(n)And

t t s0 s

1 s2

Neutron Spin RotationnnnIn 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.

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.

He,He,Re

424

0wki4

2PNC

PNCPNCPNC

Hnmf

fl

(Dmitriev et al., PhysLettB 1983)

(Michel, PhysRev 1964)

Neutron Spin Rotationin Few-Body Systems

n) liquid helium calculations have been doneinitial measurement – large errors

(n,) = (8 ± 14 (stat) ± 2 (sys)) 10-7 rad/mcurrently at NIST

nDorthodeuteriumno calculations yetproposed measurement for NIST

(np) parahydrogencalculations have been doneproposed measurement for SNS

nnn

PNC= 4lfPNC

Basic Design for Spin-rotation

• Long-wavelength, cold-neutrons ( > 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 G)

• Extract small spin-rotation signals two targets with a -coil to modulate the signal detect n with velocity separation and geometry separation

nnn

Simultaneous Signal Modulation

3He n-detectors

Analyzer

Target ChamberBack Position

Target ChamberFront Position

- Coil

Polarizer

Cold Neutron Beam

PNC

PNC PNC

BKG + PNCBKG PNC

•

•

3He n-detectors

Analyzer

Target ChamberBack Position

Target ChamberFront Position

- Coil

Polarizer

Cold Neutron Beam

PNC

PNC PNC

BKG + PNCBKG PNC

•

•

nnn

Spin-Rotation Measurementnnn

IDEAL POLARIMETER

NN

NNsin

REAL POLARIMETER

NN

NN

P1

sin

P is the measured polarization product of the polarimeter

Low Energy n Scattering in D

D2

n

n

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…

What is the extent of depolarization of the neutron transmitted through an orthodeuterium target?

Measurement of Cold Neutron Depolarization in Liquid and

Solid DeuteriumA. Komives, A. Bever, S. Carlson

DePauw University

W. M. Snow, Y. Shin, C.Y. LiuIndiana University

J. DawsonUniversity of New Hampshire

K. Kirch, M. Kasprzak, M. Kuzniak, B. Van den Brandt, P. Hautle, T. Konter, A. PichlmaierPaul Scherrer Institute

K. Bodek, S. Kistryn, J. ZejmaInstitute of Physics; Jagiellonian University

Setup for Measurement

polarizer Flipper 1

D2 target

P+

P-

1

2

N0

Polarizationanalyzerchopper

Flipper 2 detector

Flippers/chopper/analyzer/detector used in FUNSPIN beam characterization (NIM, 2005)

Side View

4 cm Solid/Liquid 98% Ortho-D220 K (Liquid)18 K (Solid)

Deuterium Target

Diameter of nearly fully grown crystal: 3.8 cm

Neutron Depolarization

PRELIMINARY PRELIMINARY

Neutron PolarizationNeutron Polarization – NormalizedTo the Empty Target Cell Values

• ~ 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

Conclusions

Spin-Rotation Measurementnnn

IDEAL POLARIMETER

NN

NNsin

REAL POLARIMETER

NN

NN

P1

sin

P is the measured polarization product of the polarimeter

Schematic of n-Spin Experiment

nnn

NIST Spectrum

Neutron Flux (1996)

0.E+00

1.E+07

2.E+07

3.E+07

4.E+07

5.E+07

6.E+07

7.E+07

8.E+07

9.E+07

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

wavelength ( angstroms )

Flu

x (

n/c

m^

2/s

)

• energies in the 10-3 eV range ( ~ 5Ǻ)

• bismuth filters provide high-energy cut-off– Choose thickness to remove < 6Ǻ(Bragg peak for ortho-D2 at 2meV, 6Ǻ.)

• Low-energy neutron filter– Høghøj et al. NIM in PhysResB 160 (2000)– Remove long wavelength neutrons

NG-6 beam line at NIST (Gaithersburg, MD)

NG-6 Spectrum 2005

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 cut-

off 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

nnn

Sensitivity Estimate (continued)

• Statistical contribution (ignore error in P)

• 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

N11

sin P

General Systematics

• Target dependent neutron scatteringbeam divergence and velocity changes for liquid vs. "empty" target (reflection off surfaces, target length changes, effective index of refraction)

• Magnetic field induced rotations (B<100G)change in rotation for change in local fields (diamagnetism of target, neutron travel time in the target region)

The cancellation of background rotations is limited bythe apparatus being the "same" for both target states.

nnn

D2 Systematics

• Diamagnetism of deuteriumB/B = 5 10-6 : for =7Ǻ, mag= 0.7 mrad in 100G field giving ~ 3 10-9 rad

change in spin rotation from magnetic susceptibility

• Deuterium material slows the n beam for 6 Ǻ neutron,v ~ 2 10-5. In 100G 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.

v/v ~ 1 %, in a 100G field and L/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 fieldEstimate 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 rotationMonitor velocity dependent systematic effects.

nnn

What We Have Done BeforeSegmented Ionization

Chamber Detector for n-4He

ORIGINAL DESIGN

Ionization Chambern + 3He → p + t

Collect charged proton and tritonon charge collection plates.

Divide charge collection plates into 4 quadrants (3" diam) separated L/R and U/D beam

nnn

What We Have Done BeforeSegmented Ionization

Chamber Detector for n-4HeORIGINAL DESIGN

Ionization Chamber3He and Ar gas mixture

4 Detection Regions along beam axis velocity separation (1/v absorption)

Gas pressure so that transverse rangeof the proton < 0.3 cm

nnn

Note region size increases for approximately equal count rates: 30% of beam in regions 1, 2, 3+4

0.5 atm 3He, 3 atm Ar gas mixture

4 detection regions along axis4 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

(Allows measurement of rotations from magnetic fields ~ 40 G)

(1996 digital picture shows 4-region, quadrant detector)

Penn et al. NIM 457, 332 (2001)

What We Have Done BeforeSegmented Ionization

Chamber Detector for n-4Hennn

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

nnn

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

nnn