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The fundamental theory of the strong interaction-quantum chromodynamics (QCD)—provides the foundational framework with which to describe and understand the key properties of atomic nuclei. A deep understanding of the explicit role of quarks and gluons in nuclei remains elusive however, as these effects have thus far been well-disguised by confinement effects in QCD which are encapsulated by a successful description in terms of effective hadronic degrees of freedom. The observation of the EMC effect has provided an enduring indication for explicit QCD effects in nuclei, and points to the medium modification of the bound protons and neutrons in the nuclear medium. Understanding the EMC effect is a major challenge for modern nuclear physics, and several key questions remain, such as understanding its flavor, spin, and momentum dependence. This manuscript provides a contemporary snapshot of our understanding of the role of QCD in nuclei and outlines possible pathways in experiment and theory that will help deepen our understanding of nuclei in the context of QCD. [ABSTRACT FROM AUTHOR]

Nuclear short-range correlations (SRCs) induce high-momentum/high-energy fluctuations in the nuclear medium. In order to assess their impact on nuclear bulk properties, like nuclear radii and kinetic energies, it is instrumental to determine how SRCs are distributed in phase space as this sheds light on the connection between their appearance in coordinate and momentum space. Using the lowest-order correlation operator approximation (LCA) to include SRC, we compute two-dimensional nuclear Wigner quasiprobability distributions w (r , k) to locate those (r , k) phase-space regions that are most heavily impacted by SRCs. The SRC-induced high-momentum components find their origin in a radial range that is confined to the nuclear interior. Significant SRCs strength is generated in the full momentum range 0 ≤ k ≲ 5 fm − 1 covered in this work, but below the Fermi momentum those are dwarfed by the mean-field contributions. As an application of w (r , k) , we focus on the radial dependence of the kinetic energy T and the momentum dependence of the radius r rms for the symmetric nuclei C 12 , Ca 40 and the asymmetric nucleus Ca 48. The kinetic energy almost doubles after including SRCs, with the largest increase occurring in the nuclear interior r ≲ 2 fm. The momentum dependence of the r rms teaches that the largest contributions stem from k ≲ 2 fm−1, where the SRCs induce a slight reduction of the order of a few percent. The SRCs systematically reduce the Ca 48 neutron skin by an amount that can be 10%. [ABSTRACT FROM AUTHOR]

Polarized electron-deuteron deep-inelastic scattering (DIS) with detection of the spectator proton ("tagged DIS") enables measurements of neutron spin structure with maximal control of nuclear effects. We calculate the longitudinal spin asymmetries in polarized tagged DIS using methods of light-front nuclear structure and study their dependence on the measured proton momentum. Asymmetries can be formed with all three deuteron spin states (± 1 , 0) or the two maximum-spin states only (±1, involving tensor polarization). The proton momentum dependence can be used to select pure S-wave configurations in the deuteron and eliminate D-wave depolarization (transverse momenta p p T ≲ 100 MeV). Free neutron spin structure can be extracted model-independently through pole extrapolation of the tagged asymmetries. Such measurements could be performed at a future electron-ion collider (EIC) with polarized deuteron beams and forward proton detectors. [ABSTRACT FROM AUTHOR]