Session GE: Mini-Symposium: Short Range Correlations and Bound Nucleon Structure Across Scales I

High-momentum nucleons in low-momentum theories

Ab-initio calculations of nuclei have seen explosive progress in recent years, thanks in part to simplifications that result from ``low resolution" inter-nucleon interactions with minimal high-momentum components, such as those from chiral effective field theory. The low resolution picture is advantageous for structure calculations since wave functions are dominated by low momenta and are less correlated, calculations are more amenable to perturbative treatments, and mean-field approaches give a reasonable starting point. In recent years there has been impressive and rapid progress in probing the short distance/high-momentum structure of nuclei using hard electron scattering, where a high resolution picture appears to be more natural. An important question to ask is, how do we reconcile the low resolution picture that is so prevalent in microscopic nuclear structure calculations, with the high resolution picture utilized in short-range correlation studi es? To address this question, I use the simplest knock-out reaction, deuteron electrodisintegration, to illustrate how high-momentum operators (and physical interpretations!) evolve as the resolution is varied using the renormalization group.   

Role of Short Range Correlations in the Neutron Skin

Recent experiments and many-body calculations indicate that approximately 20\% of the nucleons in medium and heavy nuclei $A\ge 12$ are part of short-range correlated (SRC) primarily neutron-proton . Previous work found that using chiral dynamics to account for the formation of np pairs due to the effects of iterated and irreducible two-pion exchange leads to values consistent with the 20\% level. Here chiral dynamics is applied to study how these correlations influence the calculations of neutron radii of nuclei.   

Scale and Scheme Independence and Position-Momentum Equivalence of Nuclear Short-Range Correlations

The study of Two-Nucleon Short-Range Correlations (SRCs) is an important topic in nuclear physics, and has significant implications to other fields. Obtaining a physical interpretation from Quantum Monte Carlo (QMC) calculations is very challenging, especially at small inter-nucleon distances (small-r) and high momenta (high-k). The Generalized Contact Formalism, which describes SRCs in nuclei, was used in this work to study the small-r and high-k behavior of nuclear ($2 \le A \le 40$) QMC calculations obtained using four NN potentials that differ significantly at small-r and identify which properties of SRCs are scale and scheme dependent and which are independent. We find that, while absolute abundance of SRCs (contacts) depend on the specific potential used, their ratios to d or $^4$He do not. This implies that the SRC abundance is a Mean-Field property, and inclusive (e,e') scattering experiments are insensitive to the small-r structure of the NN interaction. We demonstrate that exclusive experiments, on the other hand, can discriminate among these different NN models. We also explore the high-k, small-r equivalence of SRCs by comparing contacts extracted independently in these two regimes, and find that pn, spin-1 pair abundances are consistently the same.   

First Constraints on the Nuclear Force at Neutron Star Densities

The strong nuclear interaction between nucleons is the fundamental quantity of nuclear physics. As it cannot easily be calculated directly from QCD, it is traditionally described using parameterized effective models. While these models are well-constrained at large distances by nucleon-nucleon (NN) scattering data, its short-distance behavior is largely unconstrained, limiting our ability to theoretically describe high-density nuclear systems such as neutron stars. In this talk I will present new measurements of Short-range correlated (SRC) nucleon pairs using exclusive (e,e'NN) reactions done using the CLAS spectrometer at the Thomas Jefferson National accelerator Facility (JLab). The new data covers nucleon momenta range of 400 to 1000 MeV/c and is analyzed using the new theoretical framework of the Generalized Contact Formalism (GCF). We find that the GCF provides good kinematic agreement with data of such SRC breakup events and shows high sensitivity to the short-distance behavior of the nucleon-nucleon (NN) interaction. The data is well described by the phenomenological AV18 interaction up to 1000 MeV/c. Local Chiral interactions are also observed to provide a good description of the data up to their momentum- or position-space cutoffs.   

Studies of Proton Momentum Distribution in $^{\mathrm{4}}$He

Experimental cross sections for the $^{\mathrm{4}}$He(e,e'p)X reaction up to a missing momentum of 0.632 GeV/$c$ at x$_{\mathrm{B}}=$1.24 and Q$^{\mathrm{2}}=$2 (GeV/$c)^{\mathrm{2}}$ will be presented. The data are compared to Relativistic Distorted Wave Impulse Approximation (RDWIA) calculations for $^{\mathrm{4}}$He(e,e'p)$^{\mathrm{3}}$H channel. Significantly more events in the triton mass region are measured for p$_{\mathrm{m}}$ \textgreater 0.45 GeV/$c$ than are predicted by the theoretical model, suggesting that the effects of initial-state multi-nucleon correlations are stronger than expected by the RDWIA model.   

Probing SRC in Inverse Kinematics

Short Range Correlated (SRC) pairs are two close nucleons in the atomic nucleus. The SRC pairs are usually composed of a proton and a neutron, and have high individual and relative momentum but low common center of mass momentum. Low and high are in comparison with the nuclear Fermi momentum. The SRC pairs dominates the high tail of the nucleon momentum distribution. In the last decade the experimental SRC research was done using high energy electrons and protons to search for the pairs and study the properties of the nucleons in the pair. We present here an experiment with a new approach to study SRC in \textit{inverse kinematic} using a ${}^{12}C$ beam of 4 GeV/c/u aiming at a liquid $H_2$ target. This allows a \textit{fully-exclusive} measurement including the detection and studying of the residual A-2 nuclear system, after the 2N-SRC knockout. First measurement was done during spring 2018 in the BM@N nuclotron at the Joint Institute of Nuclear Research (JINR), Dubna, Russia. In this talk we will present some new preliminary results from that measurement.