Recent Few-Body Studies Experimental Results and Challenges Thomas B. Clegg Triangle Universities Nuclear Laboratory (TUNL) Faculty: Clegg, Crowe, Howell, Karwowski, Markoff, Tornow Current doctoral students: Couture, Esterline Recent experimental colleagues: Crowell, Daniels, Katabuchi, Weisel Theoretical collaborators: Deltuva et al. (Lisbon) Hale (LANL) Viviani et al. (Pisa) July 7, 2009 Chiral Dynamics 2009

Additional TUNL Talks Thursday in Working Group 3 at 15:00, Haiyan Gao “Study of the GDH sum rule of 3He at HIγS” Friday at 10:45, Henry Weller “Few-body reactions at low energies” High Intensity Gamma Source (HIγS) July 7, 2009 Chiral Dynamics 2009

Overview of Talk Essential goal of program Highly accurate measurements on few-nucleon systems Very low energy effects Few partial waves Non-relativistic Strenuous tests for theory Challenges and recent experimental results Ay measurements: n-p and n-3He N-d breakup measurements Spin correlation measurements in p+3He July 7, 2009 Chiral Dynamics 2009

Modeling Few-N Scattering Traditional phenomenological methods 2N (e.g. Nijmegen, CD-Bonn, AV-18) 3N (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 new fertile ‘theoretical laboratory’ Lightest system with resonant states and thresholds Simplest where spin and isospin couplings can be studied. July 7, 2009 Chiral Dynamics 2009

Test Origins of Discrepancies Chiral potentials treat 2N, 3N, and 4N interactions consistently. TUNL’s goal: provide new accurate data to help distinguish contributions. Kalantar-Nayestanaki and Epelbaum, Nucl. Phys. News 17 (2003) 22. Add to this slide a picture of the orders of interactions? July 7, 2009 Chiral Dynamics 2009

Challenge #1 - The “Ay Puzzle” Significant disagreement remains for Ay Magnitude of Ay grows with # of nucleons Expt/theory discrepancy grows with # of nucleons Barker et al., PRL 48 (1982) 918. Brune, et al., PR C63, 044013 (2001) p+d 667 keV Fisher et al, PRC74 (2006) 034001 p+p p+3He 1.00 MeV 1.60 MeV 9.05 MeV 5.05 MeV July 7, 2009 Chiral Dynamics 2009

Recent Result: n+p Polarized Neutron Source Utilizes D(dpol,npol)3He R.T. Braun, et al., Physics Letters B660 (2008)161 Polarized Neutron Source Utilizes D(dpol,npol)3He Neutron polarization ~70% Constant versus energy Liquid Scintillator Target 4He polarimeter 100 bar pressure 95% He; 5% Xe Utilizes 4He(n,n)4He Effective Ay ~ 85% July 7, 2009 Chiral Dynamics 2009

Recent Result: n+p Accurate 12 Mev Ay data. R.T. Braun, et al., Physics Letters B660 (2008)161 Accurate 12 Mev Ay data. Corrections applied for polarization-dependent detector efficiencies Data lie below predictions from phases from Nijmegen partial wave analysis. Larger π+ coupling constant needed 12 MeV July 7, 2009 Chiral Dynamics 2009

New Experiment: n+d G. Weisel, et al., private communication 16 MeV New data taken to map out energy dependence of the Ay discrepancy. New TUNL data in energy range where the ‘Ay puzzle’ disappears. Data collection complete, but multiple scattering and finite geometry corrections are not yet applied. 19 MeV 22.5 MeV 30 MeV July 7, 2009 Chiral Dynamics 2009

Challenge #2: N-d Breakup Symmetric Constant Relative Energy (SCRE) Configuration All three scattered nucleons have same CM energy α is the angle between incident beam and undetected particle α=0,180: coplanar star α=90: space star

Continuing Experiment: n-d Breakup With two detectors, the undetected particle scatters within a conical region determined by how outgoing energy and momentum are shared. Energies of the two detected particles form kinematical locus. S is the length along locus, with S=0 at intercept with neutron energy axis. Graph based on point geometry kinematic calculations. Finite geometry corrections can be significant. ΔS Space Star Point Coplanar Star

The Space Star (SST) SST Cross Section vs. Beam Energy Measured 2H(n,nn)p SST cross sections are consistently higher than theory. Measured 16.0 MeV SST cross section data are 3 standard deviations above theory. Finite geometry effects are negligible. 16.0 MeV

The Coplanar Star (CST) Measured 2H(n,nn)p (CST) cross section also larger than theory. One standard deviation discrepancy after finite geometry corrections. Dashed line is finite geometry enhancement.

Same Observable, Different Method Previous Experiments Current Experiment Previous Experiments Neutron Beam C6D12 Target Detectors A neutron and proton are detected in coincidence, 2H(n,np)n Thin CD2 foil as target Integrated beam luminosity determined by np-elastic scattering in a separate chamber downstream from main experiment (Proton Recoil Telescope) C6D12 Scintillating Target (breakup event starts clock) Two neutrons detected in coincidence using liquid organic scintillators, 2H(n,nn)p Target-beam integrated luminosity determined by n-d elastic scattering Current Experiment Neutron Detector

Challenge #3 - 4N System: n+3He J. Esterline, et al., private communication Measurements of Ay with shielded polarized neutron source from D(dpol,npol)3He. Active target is high-pressure 3He scintillator Compare with: LANL R-matrix calculations of G. Hale calculations of Deltuva et al. which use finite-range approximation of the AV-18 and CD-Bonn potentials Pol. d Beam July 7, 2009 Chiral Dynamics 2009

4N System: p+3He Prior data (~1000 points < 12 MeV) left scattering phase shift uncertainties Wisconsin analysis led to two solutions E. A. George and L. D. Knutson, Phys. Rev. C 67, 027001 (2003) Difference between solutions largest for spin-correlation coefficients below 4 MeV TUNL Doctoral Project: T.V. Daniels Measure A0y, Axx and Ayy below 5.5 MeV Determine unique energy-dependent phase shifts Previous results at 3 MeV Ayy 1 2 Aoy July 7, 2009 Chiral Dynamics 2009 16

New Experiment: p+3He Incident polarized proton beam Beam polarization measured with 4He(p,p)4He 3He target gas polarized with Rb-spin-exchange optical pumping Polarized gas batch loaded to target Target placed inside μ-metal- shielded “sine-theta coil” Incident Beam July 7, 2009 Chiral Dynamics 2009

New Experiment: p+3He Transverse 0.7 mTesla B-field produced target quantization axis Small interior field gradient achieved, ‘Coil’ current proportional to sin θ Field direction reversed in ~1 sec by rotating current pattern July 7, 2009 Chiral Dynamics 2009

New Experiment: p+3He Pyrex target cell with Kapton windows 3He pressure ~1 ATM NMR monitored 3He target polarization Calibrated NMR by 4He+3He scattering Polarization 1/e lifetime ~ 2 hrs Time July 7, 2009 Chiral Dynamics 2009

New Experiment: p+3He Target B-field steered incident beam and scattered particles Required instrumental asymmetry measurement Largest effects present and corrections applied at lowest energy and forward angles Incident Beam July 7, 2009 Chiral Dynamics 2009

New Experiment: p+3He Measured A0y, Ayy, and Axx at Ep = 2.28 , 2.77, 3.15, 4.02 and 5.54 MeV New phase shift analysis of ~1300 data All prior data < 12 MeV σ and Ay0 data of Fisher et al, PRC74 (2006) 034001 Our new measurements Unique energy-dependent phase-shift solution found Example data at Ep= 2.28 MeV A0y Ayy Axx Daniels July 7, 2009 Chiral Dynamics 2009

Unique Phase Shift Set: p+3He Singlet S-wave Phase Shift Parameter χ2 “scan” 1 2 Wisconsin result: 2 minima Need references Our result: single minimum! The addition of new data removes ambiguity and establishes unique solution! 22 22

Comparison with Theory: p+3He Promising preliminary theoretical χPT calculations using 2N at N3LO - Entem and Machleidt, PRC 68, 041001(R)(2003) 3N at N2LO – V. Bernard et al., PRC 77, 064004 (2008) Agreement for scattering lengths extracted from phase shifts This experiment: as=11.1±0.4 fm; at=9.07±0.11 fm Viviani: as =11.5 fm; at = 9.13 fm Example comparisons at 4.02 MeV M. Viviani - private communication July 7, 2009 Chiral Dynamics 2009

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 Requires 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 July 7, 2009 Chiral Dynamics 2009

Summary Low-energy, few-nucleon scattering: continues to provide the excellent data to test theoretical issues is supported by a strong community of active theorists; is providing stimulating thesis projects for doctoral students. July 7, 2009 Chiral Dynamics 2009