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3N and 4N Systems and the A y Puzzle

3N and 4N Systems and the A y 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

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3N and 4N Systems and the A y Puzzle

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  1. 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) Chiral Dynamics 2006

  2. 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 Chiral Dynamics 2006

  3. 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. Chiral Dynamics 2006

  4. p+d: Benchmark Comparisons • A. Deltuva, et al. Phys. Rev. C 71, 064003 (2005) dσ/dΩ Ay iT11 3 MeV 10 MeV 65 MeV • ~1% agreement for all calculated observables Chiral Dynamics 2006

  5. 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. Chiral Dynamics 2006

  6. T20 T21 Ayy T21 Comparisons with Data p+d, 431.3 keV • Excellent agreement also with some observables • 3N systems: σ, T20, T21, T22 Brune et al., Phys Rev C63 (2001) 44013 Chiral Dynamics 2006

  7. P+ 3He , 1.o-4.0 MeV p + 3He, 1.0 - 4.0 MeV Comparisons with Data • Excellent agreement with some observables • 4N systems: σ(θ) Fisher et al, PRC74 (2006) 034001 Fisher et al, PRC74 (2006) 034001 B. Fisher et al, PRC74 (2006) 034001 Chiral Dynamics 2006

  8. Brune, et al., PR C63, 044013 (2001) Fisher et al, PRC74 (2006) 034001 Barker et al., PRL 48 (1982) 918. p+p p+d 667 keV p+3He 1.00 MeV 1.60 MeV 5.05 MeV 9.05 MeV Glaring DiscrepanciesThe “Ay Puzzle” • Significant disagreement remains for Ay • Discrepancy grows with increasing target mass Chiral Dynamics 2006

  9. p + 3He Ay Measurements Chiral Dynamics 2006

  10. 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. [Ay(expt)-Ay(th)] / Ay(expt) p + 3He p + d• n + d o B Fisher, PRC74 (2006) 034001 Beam Energy (MeV) Chiral Dynamics 2006

  11. Origin of Discrepancy? • Are the input NN potentials correct? • Is the correct 3-nucleon interaction being used? • Is something being left out of calculations? Disagreement exists about the origin of the problem! Chiral Dynamics 2006

  12. New Experiment: n+p G. Weisel, et al. , private communication • 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. Nijmegen Polynomial Fit Chiral Dynamics 2006

  13. New Experiment: n+d G. Weisel, et al. , private communication 16 MeV • 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. 19 MeV 22.5 MeV 30 MeV Chiral Dynamics 2006

  14. New Experiment: n+3He J. Esterline, et al., private communication • 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 3.14 MeV 4.05 MeV 5.54 MeV Chiral Dynamics 2006

  15. Polarized 3He in Detectors Shielded Sine-Theta Coil Faraday cup Beam NMR Coil Target Cell New Experiment: p+3He T. Daniels, et al., private communication • 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. Chiral Dynamics 2006

  16. Rb-3He Spin-Exchange Rb 3He laser light Fermi-contacthyperfine interaction I· S Rb I • Works best for I = ½ noble gases (3He and 129Xe). • Takes minutes for 129Xe, hours for 3He. S 3He Chiral Dynamics 2006

  17. Polarized 3He Target “Overview” Katabuchi, et al., Rev. Sci. Instrum. 76, 033503 (2005) Target inside sine-theta coil Polarizer Target cell Optically pumped Rb spin-exchange polarizer Chiral Dynamics 2006

  18. Polarized 3He TargetCell • 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 Chiral Dynamics 2006

  19. Axx Ayy p+3He: New Axx and Ayy Data George and Knutson, PRC 67, 027001 (2003) • Two existing best-fit PSA solutions provide widely different p-3He zero-energy scattering lengths. Chiral Dynamics 2006

  20. Wavelength profile measured behind optical pumping cell 50 W, 25-diode laser array Grating 0.3nm FWHM 30 W to optical pumping cell ¼ wave plate 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 Chiral Dynamics 2006

  21. Polarized valence electrons of Rb atoms Polarized Rb Polarized K alkali-alkali spin exchange Hybrid Spin-Exchange Optical Pumping E. Babcock, et al., “Hybrid Spin-Exchange Optical Pumping of 3He,” PRL 91, 123003 (2003). Circularly polarized laser light (ħ per photon) Polarized 3He nuclei OP SE • Enables shorter pumping time and higher 3He polarization • New p+3He scattering measurements with these systems will begin soon. Chiral Dynamics 2006

  22. 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 Chiral Dynamics 2006

  23. 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?? Chiral Dynamics 2006

  24. Chiral Dynamics 2006

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