Unmasking short-range correlations via initial-state fluctuations in relativistic heavy-ion collisions

TL;DR

This work investigates whether nucleon-nucleon short-range correlations (NN-SRCs) imprint detectable features on the initial state of relativistic heavy-ion collisions. By incorporating NN-SRCs through a parameterized two-point function and adaptive VEGAS-based sampling, the authors show that higher-order initial-state fluctuations, encapsulated by $c_{E/S}\{n\}$, are particularly sensitive to NN correlations, with $c_{E/S}\{3\}$ and $c_{E/S}\{4\}$ differing by over 10% between correlated and uncorrelated scenarios. They demonstrate $A^{-1/3}$ and average-density scaling and reveal a linear relationship between the NN-SRC signal and the EMC effect, connecting phenomena in cold and hot QCD matter. The findings establish heavy-ion collisions as a novel probe of nuclear structure and provide a pathway to constrain two-body and many-body NN interactions across energy scales and system sizes. These results offer concrete predictions for ultra-central collisions and underscore the importance of higher-order fluctuations in interpreting final-state observables such as transverse momentum distributions.

Abstract

Although relativistic heavy-ion collisions have emerged as a powerful probe for studying nuclear structure, the potential influence of nucleon-nucleon short-range correlations (NN-SRCs) on the initial state has remained an open question. By incorporating NN-SRCs into the initial conditions, we demonstrate that higher-order fluctuations of the initial transverse size, $n$-particle $c_{E/S}\{n\}$, which can be directly mapped to final-state mean transverse momentum fluctuations, exhibit remarkable sensitivity to NN-SRCs. Quantitatively, $c_{E/S}\{3\}$ and $c_{E/S}\{4\}$ differ by more than 10\% between systems with and without NN correlations. Moreover, we report a universal scaling of these quantities with $A^{-1/3}$ and the average nuclear density, mirroring the connection between the SRC effect and the EMC effect in electron scatterings. This work establishes relativistic heavy-ion collisions as a new tool for probing nuclear structure and constraining two-body or many-body NN interactions across different energy scales and system sizes.

Figures (12)

• Figure 1: The schematic nucleon distributions from NN correlations under different $\gamma$ parameters (a) and the parameterized leading-order two-point correlations (b).
• Figure 2: The analytical results for ratios of initial-state cumulants in ultracentral $^{16}$O+$^{16}$O collisions: (a) eccentricity cumulants and (b) inverse transverse size cumulants.
• Figure 3: Ratios $R(\mathcal{Q}) = \mathcal{Q}_\text{cor} / \mathcal{Q}_\text{uncor}$ for various observables $\mathcal{Q}$ in ultracentral $^{16}$O+$^{16}$O collisions under attractive (red) and repulsive (blue) leading-order NN correlations: (a) Analytical results for a tetrahedral $4\alpha$-cluster structure, and (b) TRENTo results using a Woods-Saxon (WS) distribution.
• Figure 4: The dependence of $\Delta R(c_{E/S}\{n\})$ on $A^{-1/3}$ (top panel) and the average nuclear density (bottom panel) with AV8$'$ interaction in $^{16}$O, $^{40}$Ca and $^{208}$Pb. The coefficient of determination $R^2$ denotes the quality of the linear fitting.
• Figure 5: The linear dependence of $\Delta R(c_{E/S}\{n\})$ on the EMC effect $|\mathrm{d}R_{EMC}/\mathrm{d}x_B|$. The EMC results of $^{40}$Ca and $^{208}$Pb represents the data from SLAC and Jefferson Lab Gomez:1993riArrington:2012axCLAS:2019vsb, and the results of $^{16}$O are from Effective Field Theory Lynn:2019vwp. The linear scaling coefficient $k$ of the EMC-SRC relationship is approximately $0.08$.