1. John Arrington Argonne National Lab
Commissioning/semi-parasitic data taking on the EMC effect (and Short-Range Correlations) in light nuclei
John Arrington Argonne National Lab
Hall C Collab. Meeting,
Jan 21, 2017

2. Just how dense are nuclei?
Picture the proton as a hard sphere: R = 1.15 fm, density = 0.16 fm-3
Cubic packing of hard spheres  50% empty space
Ideal packing of hard sphere  25% empty space
To obtain densities of nuclei, can’t have ANY empty space
Can internal structure be unchanged??
Save this for after protons???
ONE OF THE BIG MYSTERIES, BIG QUESTIONS: HOW CAN PROTONS BE UNCHANGED WHEN PACKED IN SO TIGHTLY

3. Quark distributions in nuclei: EMC effect
Deeply-inelastic scattering (DIS) measures structure function F2(x)
x = quark longitudinal momentum fraction
F2(x) related to parton momentum distributions (pdfs)
Nuclear binding << energy scales of probe, proton/neutron excitations
Expected F2A(x) ≈ Z F2p(x) + N F2n(x)
F2(x) ~ S ei2 qi(x) i=up, down, strange
R = F2Fe(x) / F2D(x)
J. J. Aubert, et al., PLB 123, 275 (1983)

4. EMC effect: A-dependence
SLAC E139
Most precise large-x data
Nuclei from A=4 to 197
Conclusions
Universal x-dependence
Magnitude varies
Scales with A (~A-1/3)
Scales with density
Universal x dependence and weak A dependence make it hard to test models
J. Gomez, et al., PRD49, 4349 (1994)

5. Importance of light nuclei
Test mass vs. density dependence
4He is low mass, higher density
9Be is higher mass, low density
3He is low mass, low density (no data)
New information on A-dependence
Nuclei for which detailed structure calculations exist

6. JLab E03-103 Results 12C Consistent shape for all nuclei
(curves show shape from SLAC fit)
Measurements on 3He, 4He, 9Be, 12C
JA, D. Gaskell, spokespersons
9Be
4He
3He
If shape (x-dependence) is same for all nuclei, the slope (0.35<x<0.7) can be used to study dependence on A
J.Seely, et al., PRL103, (2009) 6 6

7. A-dependence of EMC effect
J.Seely, et al., PRL103, (2009)
Density determined from ab initio few-body calculation
S.C. Pieper and R.B. Wiringa,
Ann. Rev. Nucl. Part. Sci 51, 53 (2001)
Data show smooth behavior as density increases, as generally expected…
except for 9Be
9Be has low average density, but significant 2a+n structure; most nucleons in dense a-like configurations
Detailed nuclear structure matters
Connected to “local density” – driven by nucleons very close together?
Credit: P. Mueller

8. A-dependence of unpolarized EMC effect
4 simple models of EMC scaling:
Fraction of n(k) above 300 MeV
Average Kinetic Energy
Average Density
Nucleon Overlap (r12 < 1 fm)
Various light nuclei, differing degrees of cluster structure
Fixed normalizations for 2H for 12C
EMC slope (Normalized to 12C) 3H
3He
NEED FACTOR (A-1)/A TO COMPARE TO PREVIOUS!!!
Don’t need extra nuclei here, as it’s just prediction for EMC effect.
A-dependence of light nuclei already excludes average density
High-momentum tail has small, systematic difference for most nuclei

9. Isospin dependence vs fractional neutron excess
4 simple models of EMC scaling:
Fraction of n(k) above 300 MeV
Average Kinetic Energy
Average Density
Nucleon Overlap (r12 < 1 fm)
EMC effect isospin asymmetry: (neutron-proton)/average
Cloet estimates: scaled from NM
48Ca
9Be
Cloet, et al.
Can be probed directly in parity-violating electron scattering
48Ca measurements proposed at JLab
Light nuclei (e.g. 9Be) may also have good sensitivity; help disentangle effects

10. Unpolarized EMC measurements: JLab@12 GeV1H 2H
3He
4He
6,7Li
9Be
10,11B
12C
40Ca
48Ca Cu Au
Examine isospin dependence
SRCs at x>1 at 12 GeV
[E06-105: JA, D. Day, N. Fomin, P. Solvignon]
…help us determine if all pairs, or just np (‘fast’) pairs matter
X>1 gives correlations, high Q^2 gives quark distributions, what about x>1 at high Q^2?
A dependence in light nuclei, some with significant cluster structure
EMC effect at 12 GeV
[E10-008: JA, A. Daniel, D. Gaskell, N. Fomin]

11. Commissioning Run
E (EMC) will run concurrently with E (F2P/D) in early 2017
Both experiments included H, D data covering wide range of x, Q2
Adding Carbon allows EMC to complete Q2 scan for C/D ratios
Provides additional EMC data sets on 12C, 9Be and first data for 11B, 10B - Boron Carbide (B4C) targets
Other targets will be measured in a future run

12. EMC-SRC correlation: Importance of nuclear structure
J. Seely, et al., PRL103, (2009)
NOTHING SURPRISING WITHOUT 9BE; BOTH EFFECTS HAD ALWAYS BEEN ASSUMED TO SCALE APPROX WITH DENSITY.
N. Fomin, et al., PRL 108, (2012)
JA, A. Daniel, D. Day, N. Fomin, D. Gaskell, P. Solvignon, PRC 86, (2012)
O. Hen, et al, PRC 85, (2012)
L. Weinstein, et al., PRL 106, (2011)

13. Unpolarized EMC measurements: JLab@12 GeV1H 2H
3He
4He
6,7Li
9Be
10,11B
12C
40Ca
48Ca Cu Au
Q2 dependence for EMC ratios
A dependence of EMC effect in light nuclei, and extraction of single p(n) in A~10
…help us determine if all pairs, or just np (‘fast’) pairs matter
X>1 gives correlations, high Q^2 gives quark distributions, what about x>1 at high Q^2?
A/D ratios (small angle) for EMC-SRC correlation

15. Dense and energetic components in nuclei
N-N interaction
Hard interaction at short range
Pairs of high-momentum nucleons (up to 1 GeV/c)
Nucleon momentum distribution in 12C
n(k) [fm-3]
Mean field
part
Small N-N
separation
Dense components of nuclear wavefunction; driven by 2-body physics so independent of nuclear mass (microscopically speaking). Difficult-to-probe region but with potential impact on variety of aspects of nuclear structure (energetic, dense)
k [GeV/c]
50% of the K.E. in the deuteron comes from the ~5% of nucleons with k>250 MeV/c
Large
momenta
High-density
configurations

16. Nuclear densities and quark structure?
Nucleons are composite objects
Nucleon (RMS) diameter ~ 1.7 fm
separation in heavy nuclei ~ 1.7 fm
1.2 fm separation
0.6 fm separation
1.7 fm separation
Average nuclear density
Are nucleons unaffected by this overlap?
Do they deform as they are squeezed together?
Do the quarks exchange or interact?