September 18, 2006Chiral Dynamics N 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 Theoretical collaborators: Fonseca et al., (Lisbon), Viviani et al. (Pisa) Hale (LANL)

September 18, 2006Chiral 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 –A y in n+p, n+d, and n+ 3 He –Spin correlation measurements in p+ 3 He

September 18, 2006Chiral 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, (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, 2006Chiral Dynamics 2006 p+d: Benchmark Comparisons 3 MeV 10 MeV 65 MeV A. Deltuva, et al. Phys. Rev. C 71, (2005) dσ/dΩiT 11 AyAy ~1% agreement for all calculated observables

September 18, 2006Chiral 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, (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, 2006Chiral Dynamics 2006 Comparisons with Data Excellent agreement also with some observables –3N systems: σ, T 20, T 21, T 22 T 21 T 20 A yy Brune et al., Phys Rev C63 (2001) p+d, keV

September 18, 2006Chiral Dynamics 2006 Comparisons with Data Excellent agreement with some observables –4N systems: σ (θ) P+ 3He, 1.o-4.0 MeV p + 3 He, MeV Fisher et al, PRC74 (2006) B. Fisher et al, PRC74 (2006)

September 18, 2006Chiral Dynamics 2006 Glaring Discrepancies The “A y Puzzle” Significant disagreement remains for A y –Discrepancy grows with increasing target mass Barker et al., PRL 48 (1982) 918. Brune, et al., PR C63, (2001) p+d 667 keV Fisher et al, PRC74 (2006) p+p p+ 3 He 1.00 MeV 1.60 MeV 9.05 MeV 5.05 MeV

September 18, 2006Chiral Dynamics 2006 p + 3 He A y Measurements

September 18, 2006Chiral Dynamics 2006 Comparisons with Data The “A y 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 + 3 He p + d [A y (expt)-A y (th)] / A y (expt) n + d o B Fisher, PRC74 (2006)

September 18, 2006Chiral 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, 2006Chiral Dynamics 2006 New Experiment: n+p New TUNL 12 MeV A y data being analyzed Careful corrections applied for polarization-dependent detector efficiencies Goal: Check present 3P N-N scattering phase shifts New data lie significantly below predictions using phases from the Nijmegen partial wave analysis. Nijmegen Polynomial Fit G. Weisel, et al., private communication

September 18, 2006Chiral 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 ‘A y puzzle’ disappears. Data collection incomplete, and multiple scattering and finite geometry corrections have not yet been applied. G. Weisel, et al., private communication16 MeV 19 MeV 22.5 MeV 30 MeV

September 18, 2006Chiral Dynamics 2006 Data collection underway for A y with shielded neutron source and incident polarized beam Goal is high-accuracy measurements at low energies where p+ 3 He 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+ 3 He J. Esterline, et al., private communication 5.54 MeV 4.05 MeV 3.14 MeV

September 18, 2006Chiral Dynamics 2006 New data being collected with recently completed optically-pumped polarized 3 He target New A 0y, A yy, A xx 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+ 3 He T. Daniels, et al., private communication

September 18, 2006Chiral Dynamics 2006 New data being collected with recently completed optically-pumped polarized 3 He target New A 0y, A yy, A xx 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+ 3 He T. Daniels, et al., private communication Shielded Sine-Theta Coil Target Cell Faraday cup NMR Coil Detectors Beam Polarized 3 He in

September 18, 2006Chiral Dynamics He Rb 3 He Fermi-contact hyperfine interaction Rb Works best for I = ½ noble gases ( 3 He and 129 Xe). Takes minutes for 129 Xe, hours for 3 He.  I · S I S Rb- 3 He Spin-Exchange laser light

September 18, 2006Chiral Dynamics 2006 Polarized 3 He Target “Overview” PolarizerTarget cell Katabuchi, et al., Rev. Sci. Instrum. 76, (2005) Target inside sine-theta coil Optically pumped Rb spin-exchange polarizer

September 18, 2006Chiral Dynamics 2006 Polarized 3 He Target Cell Pyrex glass cell with Kapton windows 3 He pressure ~1 ATM NMR to monitor 3 He target polarization Calibrate NMR by 4 He+ 3 He scattering Polarization 1/e lifetime ~ 2 hrs

September 18, 2006Chiral Dynamics 2006 p+ 3 He: New A xx and A yy Data A xx A yy Two existing best-fit PSA solutions provide widely different p- 3 He zero-energy scattering lengths. George and Knutson, PRC 67, (2003)

September 18, 2006Chiral 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 3 He 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, 2006Chiral Dynamics 2006 Hybrid Spin-Exchange Optical Pumping E. Babcock, et al., “Hybrid Spin-Exchange Optical Pumping of 3 He,” PRL 91, (2003). Circularly polarized laser light ( ħ per photon) Polarized valence electrons of Rb atoms Polarized 3 He nuclei OPSE Polarize d Rb Polarize d K alkali-alkali spin exchange Enables shorter pumping time and higher 3 He polarization New p+ 3 He scattering measurements with these systems will begin soon.

September 18, 2006Chiral Dynamics 2006 Other Experimental Possibilities? n+ 3 He cross section measurements, E n < 5 MeV. n+ 3 He A 0y and spin-correlation measurements –Requires development of a high-pressure, polarized 3 He target and improved pulsed polarized neutron beam n+t, p+t measurements –Analysis of old LANL A 0y measurements in scattering –Make n+t A y measurements –Requires a sealed high-pressure tritium target

September 18, 2006Chiral 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, 2006Chiral Dynamics 2006

September 18, 2006Chiral Dynamics 2006

September 18, 2006Chiral Dynamics 2006

September 18, 2006Chiral Dynamics 2006

September 18, 2006Chiral Dynamics 2006