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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)
September 18, 2006 Chiral Dynamics 2006
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
September 18, 2006 Chiral Dynamics 2006
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.
September 18, 2006 Chiral Dynamics 2006
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
September 18, 2006 Chiral Dynamics 2006
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.
September 18, 2006 Chiral Dynamics 2006
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
September 18, 2006 Chiral Dynamics 2006
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
September 18, 2006 Chiral Dynamics 2006
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
September 18, 2006 Chiral Dynamics 2006
p + 3He Ay Measurements
September 18, 2006 Chiral Dynamics 2006
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
September 18, 2006 Chiral Dynamics 2006
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?
September 18, 2006 Chiral Dynamics 2006
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
September 18, 2006 Chiral Dynamics 2006
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
September 18, 2006 Chiral Dynamics 2006
• 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
September 18, 2006 Chiral Dynamics 2006
• 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
September 18, 2006 Chiral Dynamics 2006
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
September 18, 2006 Chiral Dynamics 2006
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
September 18, 2006 Chiral Dynamics 2006
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
September 18, 2006 Chiral Dynamics 2006
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)
September 18, 2006 Chiral Dynamics 2006
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
September 18, 2006 Chiral Dynamics 2006
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.
September 18, 2006 Chiral Dynamics 2006
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
September 18, 2006 Chiral Dynamics 2006
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, 2006 Chiral Dynamics 2006