John Arrington Argonne National Lab

1. 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??

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)~ Sei2qi(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 4Heis low mass, higher density 9Beis 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, 202301 (2009) 6

7. A-dependence of EMC effect J.Seely, et al., PRL103, 202301 (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 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 GeV 1H 2H 3He 4He 40Ca 48Ca Cu Au 6,7Li 9Be 10,11B 12C Examine isospin dependence SRCs at x>1 at 12 GeV [E06-105: JA, D. Day, N. Fomin, P. Solvignon] 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 • E12-06-105 (EMC) will run concurrently with E12-10-002 (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, 202301 (2009) N. Fomin, et al., PRL 108, 092052 (2012) JA, A. Daniel, D. Day, N. Fomin, D. Gaskell, P. Solvignon, PRC 86, 065204 (2012) O. Hen, et al, PRC 85, 047301 (2012) L. Weinstein, et al., PRL 106, 052301 (2011)

13. Unpolarized EMC measurements: JLab@12 GeV 1H 2H 3He 4He 40Ca 48Ca Cu Au 6,7Li 9Be 10,11B 12C Q2 dependence for EMC ratios A dependence of EMC effect in light nuclei, and extraction of single p(n) in A~10 A/D ratios (small angle) for EMC-SRC correlation

15. Dense and energetic components in nuclei Hard interaction at short range N-N interaction 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 k [GeV/c] 50% of the K.E. in the deuteron comes from the ~5% of nucleons with k>250 MeV/c High-density configurations Large momenta

16. Nuclear densities and quark structure? Nucleons are composite objects Nucleon (RMS) diameter ~ 1.7 fm separation in heavy nuclei ~ 1.7 fm 1.7 fm separation 1.2 fm separation 0.6 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?