Long Range Outlook for Short-Range Correlations

TL;DR

Short-range correlations (SRCs) encode high-momentum, short-distance components of the nuclear ground state and potentially reveal explicit QCD dynamics in nuclei. The paper surveys modern SRC experiments across electron, hadron, and photon probes, and surveys high-energy and many-body theories (light-front dynamics, generalized contact formalism, SRG, QMC) that connect ground-state structure to SRC observables and cross sections. It highlights universal two-nucleon SRC behavior, strong np dominance at moderate to high missing momenta, and the ongoing pursuit of 3N-SRCs and non-nucleonic degrees of freedom, outlining a roadmap for future measurements and theory. The work aims to achieve a scale- and probe-independent understanding of SRCs with broad implications for dense matter, nuclear forces, and QCD-related dynamics in nuclei.

Abstract

Short range correlated (SRC) N N pairs are pairs of nucleons with high relative momentum (prel > kF where kF ~ 250 MeV/c is the Fermi momentum in medium to heavy nuclei) and lower center of mass momentum. The motivation for studying SRC pairs ranges from a desire to achieve a more comprehensive understanding of the many-body nuclear wave-function at high-resolution to searching for explicit QCD-dynamics effects within the nuclear medium, not to mention connections to many other open problems in nuclear physics. Exploring short-range correlations was one of the physics motivations for building CEBAF (now Jefferson Lab). Scientists used the high luminosity and high energy of this cutting-edge machine to find kinematics that cleanly showed the signals of short-range correlations. This paved the way in the last two decades for tremendous progress understanding these correlations. This paper reviews recent progress and highlights outstanding questions and areas that need further study.

Figures (16)

• Figure 1: Left: Inclusive cross section ratios for helium nuclei from E02-019 in Hall C Fomin:2012. Right: extracted values of $a_2$ vs $A$ from measurements at SLAC Frankfurt:1993sp, CLAS 2006 Egiyan:2006, Hall C Fomin:2012 , CLAS 2020 Schmookler:2019nvf and Hall A Li:2022fhh.
• Figure 2: The SRC scaling ratio, $a_2-1$, plotted versus the effective nuclear density. Data are from Fomin:2012, and the scaled nuclear density is the density from the ab initio structure calculation Carlson:2014vla, scaled by $(A-1)/A$ to remove the contribution of the struck nucleon.
• Figure 3: Tritium to helium-3 $(e, e^\prime)$ cross-section ratio, $\sigma _{^3H}/\sigma _{^3He}$, at $Q^2 \sim 1.4$ GeV$^2$ (red) and $Q^2 \sim 1.9$ GeV$^2$ (blue) as a function of $x_B$. The experimental data is taken from Ref. Li:2022fhh. The blue and curves are calculations from Sargsian sargsian14, Benhar Benhar:1993jaBenhar:2013dq, and Schmidt Schmidt:2024fok for $Q^2=1.9$ and 1.4 GeV$^2$, respectively. Reproduced from Li:2024rzf
• Figure 4: Per nucleon $^4$He/$^3$He ratios from three JLab experiments egiyan06fomin12Ye:2017mvoZHANG2025140087. The high-$x_{\mathrm{bj}}$ coverage reaches the kinematic region associated with the expected onset of 3N-SRC ($\alpha_{3N} > 1.6$) and extends into the range where a second scaling plateau might occur ($\alpha_{3N} > 1.8$).
• Figure 5: Per-nucleon $(e,e'p)$ cross-section ratios for carbon relative to deuterium as a function of $x_B$ (left panel) and $p_{miss}$ (right panel). (left) The filled symbols show the data integrated from $p_{miss}^{min}\le p_{miss}\le 600 MeV/c$ The colored bands represent the total uncertainty, including both statistical and point-to-point systematic uncertainties, at the $68$% confidence level. The open square show the corresponding per-nucleon $(e,e')$ cross section ratios. (right) the cross-section ratios are integrated over the $0.7~\leq~x_B\leq1.8$. The green circles denote the experimental data. The brown line represents calculated cross sections for scattering off short-range correlated (SRC) nucleons in carbon, using the GCF model, while the other lines correspond to calculations for one-body mean-field nucleons, obtained from the QMC (teal), IPSM (black), and Skyrme (azure) models. The IPSM and Skyrme calculations were normalized to the data at $p_{miss} \le 150$ MeV/c. Figure taken from CLAS:2022odn.