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

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

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)

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)

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

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 6

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

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

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

Unpolarized EMC measurements: JLab@12 GeV 1H 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]

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

EMC-SRC correlation: Importance of nuclear structure J. Seely, et al., PRL103, 202301 (2009) NOTHING SURPRISING WITHOUT 9BE; BOTH EFFECTS HAD ALWAYS BEEN ASSUMED TO SCALE APPROX WITH DENSITY. 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)

Unpolarized EMC measurements: JLab@12 GeV 1H 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

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

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?