1. Argonne National Laboratory
PR Precision measurement of the isospin dependence in the 2N and 3N short range correlation region
Spokespersons:
J. Arrington, D. B. Day, D. Higinbotham, P. Solvignon
John Arrington
Argonne National Laboratory
PAC38
August 25, 2011

2. Short range correlations (SRC)
Short-range NN interaction generates high momenta
Universal mechanism for all nuclei
Similar shape for k>kFermi
Cioffi Degli Atti et al, PRC53, 1689 (1996) 2

3. Short range correlations (SRC)
Short-range NN interaction generates high momenta
Universal mechanism for all nuclei
Similar shape for k>kFermi
Mean-field region: collective behavior, strongly A-dependent
Cioffi Degli Atti et al, PRC53, 1689 (1996) 3 3

4. Short range correlations (SRC)
Short-range NN interaction generates high momenta
Universal mechanism for all nuclei
Similar shape for k>kFermi
High-momentum region: short-range physics, largely A-independent.
Dominated by 2N-SRC tail
A(e’,e) at x>1:
For momentum sufficiently above kFermi, mean field contributions small; dominated by 2N-SRCs
Cioffi Degli Atti et al, PRC53, 1689 (1996) 4 4

5. Short range correlations (SRC)
Pmin vs. x, Q2
k>kFermi
A(e’,e) at x>1:
For momentum sufficiently above kFermi, mean field contributions small; dominated by 2N-SRCs
Cioffi Degli Atti et al, PRC53, 1689 (1996) 5 5

6. SRC evidence at JLab Simple SRC Model:
K. Egiyan et al, PRL96, (2006)
Simple SRC Model:
1N, 2N, 3N contributions dominate at x≤1,2,3
2N, 3N configurations “at rest” (total ppair = 0)
Isospin independent
N. Fomin, et al, arXiv: (2011)
Experimental observations:
Clear evidence for 2N-SRC at x>1.5
Suggestion of 3N-SRC plateau
Isospin dependence ? 6 6

7. Tensor force dominance
R. Subedi et al, Science 320, 1476(2008)
Tensor force dominance
Simple SRC Model:
1N, 2N, 3N contributions dominate at x≤1,2,3
2N, 3N configurations “at rest” (total ppair = 0)
Isospin independent
R. Schiavilla, R. Wiringa, S. Pieper and J. Carlson, PRL98, (2007) pp np
Scaled deuteron momentum distribution
From A(p,p’pn) and 12C(e,e’pN):
90% of observed pN pairs are pn; tensor force  isosinglet dominance
R(pp/pn) = 0.0560.018
R(T=1/T=0) = 208% 7

8. Main physics goals: E12-11-112
Isospin-dependence
Triple coincidence:
Demonstrated isoscalar dominance
Good precision: R(T=1/T=0) = 208%
Large FSI: Dominates the high-Pm 12C(e,e’p) events used to look for SRCs
Inclusive 3H/3He:
Improved precision: Extract R(T=1/T=0) to 3.8%
FSI much smaller (inclusive) and expected to cancel in ratio
No Pm dependence
3N SRCs structure (momentum-sharing and isospin)
Q2 dependence can test models of the momentum sharing
3He/3H ratio very sensitive to isospin-momentum correlations
Improved A-dependence in light and heavy nuclei
Average of 3H, 3He  A=3 “isoscalar” nucleus
Determine isospin dependence  improved correction for N>Z nuclei, extrapolation to nuclear matter
Absolute cross sections (and ratios) for 2H, 3H, 3He
Test calculations of FSI for simple, well-understood nuclei 8 8

9. Isospin structure of 2N-SRCs
3He/3H is simple/straightforward case:
Simple estimates for 2N-SRC
Isospin independent
Full n-p dominance (no T=1)
40% difference between full isosinglet dominance and isospin independent
Few body calculations [M. Sargisan, Wiringa/Peiper (GFMC)] predict n-p dominance, but with sizeable contribution from T=1 pairs
Goal is to measure 3He/3H ratio in 2N-SRC region with 1.5% precision
 Extract R(T=1/T=0) with uncertainty of 3.8%
Extract R(T=1/T=0) with factor of two improvement over previous triple-coincidence, smaller FSI 9

10. 3N-SRC configurations p3 = p1 + p2 p1 = p2 = p3
Different configurations possible for 3N-SRCs, for example:
“Linear configuration”
p3 = p1 + p2
extremely large momentum
“Star configuration”
p1 = p2 = p3
Inclusive measurement can help to differentiate between these configurations and test isospin structure 10 10

11. Light-cone fraction: a2n
Relativistic: x  a [light cone momentum fraction]
a = A(Ei-pi,z)/(EA-pA,z) = A(Eilab-pi,zlab)/MA
Cannot reconstruct in inclusive scattering, but for scattering from 2N-SRC, a ≈ a2N
For 3N-SRC, equivalent a3N depends on the details of the momentum sharing in the SRC
Ratios vs x
Combine with E data on 3He
Quality of scaling in a3N tests picture of 3N-SRC momentum sharing
Ratios vs a2N 11 11

12. R≠1.4 implies isospin dependence AND non-symmetric momentum sharing
Momentum-isospin correlations
“Linear configuration”
p3 = p1 + p2
extremely large momentum
“Star configuration”
p1 = p2 = p3
(a) yields R(3He/3H) ≈ 3.0 if nucleon #3 is always the doubly-occurring nucleon
(a) yields R(3He/3H) ≈ 0.3 if nucleon #3 is always the singly-occurring nucleon
(a) yields R(3He/3H) ≈ 1.4 if configuration is isospin-independent, as does (b)
R≠1.4 implies isospin dependence AND non-symmetric momentum sharing 12 12

13. (3He+3H)/2H yields `isoscalar’ A=3 result
A-dependence of 2N-SRCs
N. Fomin, et al, arXiv: (2011)
Red points: assume isosinglet dominance
Cyan points: assume isospin independence
Reality is somewhere in between (closer to isosinglet dominance)
Large difference for 3He and 9Be, heavy nuclei  modifies A-dependence for light nuclei and extrapolation to nuclear matter
(3He+3H)/2H yields `isoscalar’ A=3 result
3He/3H yields improved extraction of (T=1)/(T=0)  better correction for all non-isoscalar nuclei 13 13

14. Extra impact of improved A-dependence
2N-SRC ratio
EMC effect
3He
4He
9Be C
Cu,Au
Extra impact of improved A-dependence
Correlation between EMC effect and SRCs suggests that they may both be driven by short-distance physics (density) or high-momentum physics (virtuality)
L. Weinstein, et al., PRL 106:052301,2011
Improved measurements of A-dependence of SRCs can test different interpretations;
Requires better quantification of isosinglet “dominance”

15. Quasielastic data Worlds 3H QE data: Q2 ≤ 0.9 GeV2
Propose: GeV2
1.4,1.7 GeV2
GeV2
In PWIA, 3He/3H with 1.5% uncertainty corresponds to 3% on GMn
* Limited to Q2≤1 GeV2, where QE peak has minimal inelastic contribution
* This is the region with ~8% discrepancy between the Anklin, Kubon data and
the CLAS ratio and Hall A polarized 3He extractions
Nuclear effects expected to be small, largely cancel in ratio
For CLAS D(e,e’n)/D(e,e’p) extraction of GMn, nuclear corrections on the ratio were <0.1% over the full Q2 range

16. PR12-11-112: Experimental setup
Standard Hall A HRS configuration
Gas Cerenkov + Calorimeter PID
1H, 2H, 3H, 3He room temperature cells, 20 atmospheres (10 for 3H)
Empty cell for window subtraction (check software cut on windows, subtract residual contribution)
Carbon foils for optics 16

17. Tritium target: updated design
Four identical cells: 1H, 2H, 3He at 20 atmospheres, 3H at 10 atm.
Operate at room temperature
Length: 30cm, Diameter: 1.25cm
18 mil windows and walls
Technical review last year
Prototype requested and funded
Goal is to be ready by 2014

18. Kinematic coverage QE 2N 3N Beam current: 25 mA, unpolarized
Raster interlock
Beam energy: 4.4, (2.2) GeV
17.5 Days 4.4 GeV [main production]
1.5 days 2.2 GeV [checkout+QE] QE 2N 3N 18

19. Kinematic coverage QE 2N 3N Left HRS running (380 hours)
Beam current: 25 mA, unpolarized
Raster interlock
Beam energy: 4.4, (2.2) GeV
17.5 Days 4.4 GeV [main production]
1.5 days 2.2 GeV [checkout+QE] QE 2N 3N
Left HRS running
(380 hours) 19

20. Kinematic coverage QE 2N 3N Right HRS running (parasitic)
Beam current: 25 mA, unpolarized
Raster interlock
Beam energy: 4.4, (2.2) GeV
17.5 Days 4.4 GeV [main production]
1.5 days 2.2 GeV [checkout+QE] QE 2N 3N
Right HRS running
(parasitic)
Worlds 3H QE data: Q2 ≤ 0.9 GeV2
Left HRS running
(380 hours) 20 20

21. Summary
Study of isospin dependence of 2N-SRC from 3H/3He from inclusive scattering: will complement the results of 2N knockout experiments
Greater precision
Smaller final-state interactions
First look at isospin-momentum structure in 3N-SRC region
Quasi-elastic data on 3H and 3He for Q2-values of (GeV/c)2
Beam time requested: 19 days including data taking, calibrations, background studies and configuration changes
Hall A spectrometers in standard configuration, same 3H target system needed for the approved MARATHON experiment (E ) 21

22. Backup Slides 22

23. Relationship to E08-014 (“x>2” on light nuclei)
E08-014: Finished data taking in April/May
Extract Q2 dependence for 3He/2H, 4He/3He ratios
Precisely determine scaling regions for 2N, 3N-SRCs in light nuclei
Initial Q2 dependence of ratios vs. different 3N scaling variables (a3N)
Isospin (40Ca/48Ca)
Intrinsic sensitivity is roughly half of 3H/3He
Total uncertainty in R(T=1/T=0) about 12% (40Ca target problems) PR
Difference of 3H, 3He to study (T=1)/(T=0)
Project 3.8% uncertainty compared to 8% from (e,e’pN), 12% from 40/48Ca
Yield improved isoscalar correction for light and heavy nuclei
Look for asymmetry in momentum-isospin distribution for 3N SRCs
Average of 3H, 3He yields “isoscalar” A=3 nucleus
Improve extraction of A-dependence of SRCs in light nuclei
Comparison to state-of-the-art calculations without isospin structure uncertainties 23 23

24. Final-state interactions
No indication of Q2-dependent FSI
* A/D ratios in plateau region
No indication of FSI within 2N-SRC
* nD(k) from y-scaling vs. calculations
* high-k data consistent with calculations
* Scatter of NN potentials limits constraints
SLAC [Fe]
CLAS [Fe]
Hall C [Fe] – E89-008
Hall C [Cu] – E02-019 24 24

25. Dummy and 3He targets (E08-014, kin 6.5)

26. SRC evidence at SLAC, JLab Hall B, Hall C
Frankfurt, Strikman, Day, Sargsian, PRC48, 2451 (1993)
Naïve SRC Model:
1N, 2N, 3N contributions dominate at x≤1,2,3
2N, 3N configurations “at rest”
Isospin independent
Experimental observations:
Evidence of 2N-SRC at x>1.5
Suggestion of 3N-SRC plateau
Isospin dependence ? 26 26

27. QE peak at low Q^2

28. Onset of 2N SRC region is not A-independent2H
197Au

29. Acceptance correction
Systematics
δσ/σ
δR/R
(normalization)
(pt-to-pt)
Acceptance correction
2.0%
0.3%
1.0%
Radiative correction
3.0%
0.4%
Tracking efficiency -
0.2%
Trigger efficiency
0.5%
0.1%
PID efficiency
1.5%
Target thickness
1.0%*
Charge measurement
Energy measurement
0.05%
COMBINED UNCERTAINTY
4.6%
1.1%
1.2%
* Expect to know relative target thickness to <2%, and be able to normalize to DIS at the 1% level (based on MARATHON proposal) 29

30. EMC slope vs SRC
• EMC slopes are fit from 0.325<x<0.7; preliminary results from SRC, EMC (heavy nuclei)
• Some kind of break down for heavy nuclei, SRC factors are more or less same but EMC slope keep on increasing with A
Without deuteron “constraint” point, fit does not have expected behavior for deuteron
Rescaling assuming n-p only in SRC, all N-N pairs in EMC fixes linearity, deuteron limit. Suggests short-distance over high-momentum?