1. 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

2. 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

3. 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

4. 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, (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

5. 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

6. 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, (2001)
p+d
667 keV
Fisher et al, PRC74 (2006)
p+p
p+3He
1.00 MeV MeV
9.05 MeV
5.05 MeV
July 7, 2009
Chiral Dynamics 2009

7. 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

8. 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

9. 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

10. 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

11. 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

12. 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

13. 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.

14. 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

15. 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

16. 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, (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

17. 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

18. 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

19. 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

20. 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

21. 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)
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

22. 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

23. Comparison with Theory: p+3He
Promising preliminary theoretical χPT calculations using
2N at N3LO - Entem and Machleidt, PRC 68, (R)(2003)
3N at N2LO – V. Bernard et al., PRC 77, (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

24. 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

25. 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