September 18, 2006Chiral Dynamics 2006 3N and 4N Systems and the A y Puzzle Thomas B. Clegg for TUNL...

September 18, 2006 Chiral Dynamics 2006

3N and 4N Systems and the Ay Puzzle

Thomas B. Clegg for TUNL Collaborators

Faculty: Clegg, Karwowski, Ludwig, Tornow

Current graduate students: Arnold, Couture, Daniels, Esterline,

Former experimental colleagues: Brune, Fisher, Katabuchi, Weisel

Theoretical collaborators: Fonseca et al., (Lisbon), Viviani et al. (Pisa)

Hale (LANL)


Outline• What physics is being investigated?

– Recent theoretical advances– Theoretical comparisons with data: most

are good– Glaring discrepancies remain: what is

their origin?

• New experiments are underway – Ay in n+p, n+d, and n+3He

– Spin correlation measurements in p+3He


Modeling Few-N Scattering

• Start with modern NN potentials– Nijmegen, CD-Bonn, AV-18– 3N interaction, e.g. Urbana IX

• Use these to calculate observables in 3N & 4N systems– Coordinate vs. momentum space descriptions – “Benchmark calculation for proton-deuteron elastic scattering

observables including the Coulomb interaction,” A. Deltuva, et al. Phys. Rev. C 71, 064003 (2005)

• 4N system is becoming a fertile ‘theoretical laboratory’– Lightest system with resonant states and thresholds– Simplest where systems of isospin T=3/2 can be

studied.


p+d: Benchmark Comparisons

3 MeV

10 MeV

65 MeV

A. Deltuva, et al. Phys. Rev. C 71, 064003 (2005)

dσ/dΩ iT11Ay

~1% agreement for all

calculated observables


Modeling Few-N Scattering

• Start with modern NN potentials– Nijmegen, CD-Bonn, AV-18– 3N interaction, e.g. Urbana IX

• Use these to calculate observables in 3N & 4N systems– Coordinate vs. momentum space descriptions – “Benchmark calculation for proton-deuteron elastic scattering

observables including the Coulomb interaction,” A. Deltuva, et al. Phys. Rev. C 71, 064003 (2005)

• 4N system is becoming a fertile ‘theoretical laboratory’– Lightest system with resonant states and thresholds– Simplest where systems of isospin T=3/2 can be

studied.


Comparisons with Data

• Excellent agreement also with some observables– 3N systems: σ, T20, T21, T22T

21T

21T

20A

yy

Brune et al., Phys Rev C63 (2001) 44013

p+d, 431.3 keV


Comparisons with Data

• Excellent agreement with some observables– 4N systems: σ(θ)

P+ 3He , 1.o-4.0 MeV

p + 3He, 1.0 - 4.0 MeVFisher et al, PRC74 (2006) 034001

Fisher et al, PRC74 (2006) 034001

B. Fisher et al, PRC74 (2006) 034001


Glaring DiscrepanciesThe “Ay Puzzle”

• Significant disagreement remains for Ay

– Discrepancy grows with increasing target mass

Barker et al., PRL 48 (1982) 918. Brune, et al., PR C63, 044013 (2001)

p+d667 keV

Fisher et al, PRC74 (2006) 034001

p+p p+3He 1.00 MeV 1.60 MeV

9.05 MeV

5.05 MeV


p + 3He Ay Measurements


Comparisons with Data The “Ay Puzzle”

• Differences between experiment and theory with 3NF persist for several targets and over a significant energy range – Fractional difference is

nearly constant for 3N systems at low energy

– These differences vanish above 40 MeV.

Beam Energy (MeV)

p + 3He

p + d •[A

y(exp

t)-A

y(th

)] /

A

y(exp

t) n + d o

B Fisher, PRC74 (2006) 034001


Disagreement exists about the origin of the problem!

• Are the input NN potentials correct?

• Is the correct 3-nucleon interaction being used?

• Is something being left out of calculations?

Origin of Discrepancy?


New Experiment: n+p

• New TUNL 12 MeV Ay data being analyzed

• Careful corrections applied for polarization-dependentdetector efficiencies

• Goal: Check present 3P N-Nscattering phase shifts

• New data lie significantly below predictions using phases from the Nijmegen partial wave analysis.

NijmegenPolynomial Fit

G. Weisel, et al. , private communication


New Experiment: n+d

• New data being taken to map out the energy dependence of the discrepancy.

• New TUNL data in energy range where the ‘Ay puzzle’ disappears.

• Data collection incomplete, and multiple scattering and finite geometry corrections have not yet been applied.

G. Weisel, et al. , private communication 16 MeV

19 MeV

22.5 MeV

30 MeV


• Data collection underway for Ay with shielded neutron source and incident polarized beam

• Goal is high-accuracy measurements at low energies where p+3He data were taken by Fisher et al.

• Compare with: – R-matrix calculations of G. Hale – calculations of A. Fonseca et al.

which use finite range approximation of the CD-Bonn potential

New Experiment: n+3HeJ. Esterline, et al., private communication

5.54 MeV

4.05 MeV

3.14 MeV


• New data being collected with recently completed optically-pumped polarized 3He target

• New A0y, Ayy, Axx data between 2 and 6 MeV

• Plan new phase-shift analysis of all new and existing data

• Compare with most recent calculations of Viviani et al.

New Experiment: p+3He T. Daniels, et al., private communication

Shielded Sine-Theta

Coil

Target Cell

Faraday cup

NMR Coil

Detectors

Beam

Polarized 3He in


3He

Rb

3He

Fermi-contact hyperfine interaction

Rb

• Works best for I = ½ noble gases (3He and 129Xe).

• Takes minutes for 129Xe, hours for 3He.

I · S

I

S

Rb-3He Spin-Exchange

laser light


Polarized 3He Target “Overview”

Polarizer Target cell

Katabuchi, et al., Rev. Sci. Instrum. 76, 033503 (2005)

Target insidesine-theta coilOptically pumped

Rb spin-exchange polarizer


Polarized 3He Target Cell

• Pyrex glass cell with Kapton windows• 3He pressure ~1 ATM• NMR to monitor 3He target

polarization• Calibrate NMR by 4He+3He scattering• Polarization 1/e lifetime ~ 2 hrs


p+3He: New Axx and Ayy Data

Axx Ayy

• Two existing best-fit PSA solutions provide widely different p-3He zero-energy scattering lengths.

George and Knutson, PRC 67, 027001 (2003)


New Narrowed Laser System

• Use external optical cavity with grating to narrow laser linewidth from 3 nm to 0.3 nm• More efficient use of light enables higher 3He polarization

Wavelength profile measured behind optical pumping cell

50 W, 25-diode laser array

30 W to optical pumping cell

Grating

¼ wave plate

0.3nm FWHM


Hybrid Spin-Exchange Optical PumpingE. Babcock, et al., “Hybrid Spin-Exchange Optical Pumping of 3He,” PRL 91, 123003 (2003).

Circularly polarized laser light

(ħ per photon)

Polarized valence

electrons of Rb atoms

Polarized 3He nuclei

OP SEPolarize

d

Rb

Polarized

K

alkali-alkali spin

exchange

• Enables shorter pumping time and higher 3He polarization

• New p+3He scattering measurements with these systems will begin soon.


Other Experimental Possibilities?

• n+3He cross section measurements, En< 5 MeV.

• n+3He A0y and spin-correlation measurements– Requires development of a high-pressure, polarized

3He target and improved pulsed polarized neutron beam

• n+t, p+t measurements– Analysis of old LANL A0y measurements in

scattering

– Make n+t Ay measurements

– Requires a sealed high-pressure tritium target

pt


Summary

• Low-energy, few-nucleon scattering:– is providing the best possible data to

resolve current theoretical issues;– is supported by a strong community of

active theorists;– is providing stimulating thesis projects for

doctoral students.

• But, what is most important to measure next??

September 18, 2006Chiral Dynamics 2006 3N and 4N Systems and the A y Puzzle Thomas B. Clegg for TUNL...

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