1. R. Alarcon, APFB 2017, August 25-30, Guilin, China
Vector and Tensor Asymmetries from the 2H(e,e’p) Reaction in Quasielastic Scattering
R. Alarcon, APFB 2017, August 25-30, Guilin, China

2. Scientific Motivation
The deuteron's simple structure enables reliable calculations to be performed in sophisticated theoretical frameworks.
Spin-dependent quasielastic (e,e’p) from both vector and tensor polarized deuterium provides unique access to the orbital angular momentum structure of the deuteron, which is inaccessible in unpolarized scattering.
To see the direct effects of the D-state, initial-state momenta up to 500 MeV/c are required.
 Nucleon-nucleon correlations with high relative momenta are known to play a significant role in nuclear structure.
The combination of a pure, highly polarized gas target internal to a storage ring with an intense, highly polarized electron beam and a large acceptance detector allows the simultaneous measurement of the asymmetries as a function of initial-state proton momentum and momentum transfer.

3. MIT-Bates Linear Accelerator Center
Linac: 2×500 MeV
Beam: 850 MeV / Imax = 225 mA / Pe = ±0.007 ±0.04
SHR: Siberian Snake + Compton Polarimeter
Target: Internal Target + Atomic Beam Source

4. Internal Target and Atomic Beam Source
Dissociator breaks D2 into atoms
Sextupoles
selectively focus/defocus hyperfine states
RF transition units
induces transition between hyperfine states
Access to ALL polarization states of 2D
operates in 3 polarization states
(-Pz, +Pzz) (+Pz, +Pzz) (0, -2Pzz)
Internal target
pure, no target chamber component in beam line
Beam
D2 Gas
Target Cell
An Atomic Beam Source was used to produce polarized deuterium gas target for this experiment.
The ABS has a few components.
From the top, the dissociator breaks deuterium molecules into atoms, the sextupoles are radial stern galarch devices that focus and defocus the atoms depending on their hyperfine states. The RF transition units induce transitions between hyperfine states.
The efflux from the ABS is highly polarized atomic deuterium gas with access to all the spin states the deuteron. For this experiment, the target spin is flipped among three states, with different values in the vector and tensor polarization. Vector asymmetries were measured between the two states with opposite vector polarization, these are the topic of dissertation by Dr. Pete Karpius, Dr. Aaron Maschinot, Dr. Nikolas Meitanus and Dr. Vitaliy Ziskin. This work measures the tensor asymmetry in the ed-elastic channel between the states with opposite tensor polarizatoins.
The polarized deuterium gas were injected into a storage cell embedded in the beam line. The atoms bump around in the cell and were pumped out when they exited the target cell from the two ends.
Just to give a feeling of the target performance, the luminosity we operated at was a few 10^31 and the target tensor polarization was about 60%.

5. Atomic Beam Source Performance
Target Flow Intensity: 2  1016 atoms/s Luminosity: 4  mA
Vector Polarization:
Quasielastic peak 2H(e,e’p)
hPz = ± ±
hPz = ± ±
Tensor Polarization:
T20 elastic
Pzz = ± ± ±0.034
Pzz = ± ± ±0.028

6. Bates Large Acceptance Spectrometer Toroid (BLAST)
Left-Right symmetry
Large Acceptance
0.1 < Q2/(GeV/c)2 < 1.0
Coils: B = 3.8 kG
Drift Chambers
PID, tracking
 ≈ 0.5º,
Cerenkov Counters
e,  separation
Scintillators
TOF, PID, trigger

7. The BLAST Collaboration

8. Kinematics and Observables
Electrodisintegration of the Deuteron
Quasi-elastic 2H(e,e’p)
Beam + Target Polarized
In the Born approximation Ae , AVd, and ATed  are all zero.
In a purely S-state ATd is also zero, but will vary from zero as D-state contributions become important providing a measure of the tensor component of the NN interaction.
Similarly, AVed  will vary from hPz  as D-state contributions become significant.

9. Kinematics and Observables
R(h,Pz,Pzz): charge normalized yield or event rate for each spin orientation combination

10. Experimental Layout

11. Experimental Layout protons Electron - Right Sector
“Parallel” Kinematics
* ≈ 0
electrons
Same Sector Kinematics

12. Experimental Layout Neutrons electrons Electron - left sector
“Perpendicular” Kinematics
* ≈ 90
protons
electrons
Opposite Sector Kinematics

13. BLAST Experimental Data
3 MC integrated charge delivered to BLAST
Programs for polarized hydrogen and vector/tensor polarized deuterium
Deuterium run1, spin angle 31º
450 kC charge (169 pb-1), Pz= 85%, Pzz=66%
Deuterium run2, spin angle 47º
550 kC charge (150 pb-1), Pz=70%, Pzz=54%
Asymmetries measured 0.1 < Q2/(GeV/c)2 < 0.5

14. Data Reduction and Analysis
Quasielastic events were selected by placing a 2.5σ cut around the peak of the missing mass spectrum representing the remaining neutron.  
After background subtraction and correcting for false asymmetries (empty target) the yields in Q2  and pm  are determined for the combinations of beam and deuterium vector and tensor orientations.

15. Beam-Vector Asymmetries

16. Beam-Vector Asymmetries

17. Summary of Beam-Vector Results
PRL 88, (2002)

18. Tensor Asymmetries

19. Tensor Asymmetries

20. Summary of Tensor Results
The PWBA calculations show that the sign is different in same sector  and opposing sector  kinematics.
The ATd data at pm > 250 MeV/c are particularly sensitive to the tensor part of the interaction at short distances, where it has significant model dependence.  
It is to be noted that the theoretical model used here works well, given that it is mainly based on nucleon degrees of freedom.
PRL 82, 687 (1999)

21. Conclusions
New data for the vector AVed and tensor ATd spin asymmetries from the deuteron for a Q2  range from 0.1 to 0.5 (GeV/c)2 .
The asymmetries were mapped out in momentum space for quasielastic kinematics (e, e’p) for a range of pm  from approximately 0 to 500 MeV/c.
These new data provide a strong constraint on our understanding of deuteron structure and the tensor force between a neutron and a proton.
The measurements were carried out with an internal gas target of polarized deuterium that allowed injection of the spin substates in a manner that minimized systematic errors.
The data reported here were taken simultaneously with precise measurements of the elastic channel (PRL 107, (2011)) and the (e, e’n ) channel (PRL 101, (2008)).

22. Atomic Beam Source