Testing a Linear Relation: Short-Range Correlations and the EMC Effect for Gluons and Quarks in Nuclei

TL;DR

The paper addresses whether a linear relation ties short-range correlations (SRCs) to the EMC effect for gluons and quarks in nuclei. It tests the gluon relation by correlating the slope of the DIS reduced cross section ratio $-\mathrm{d}R_A^{c\bar{c}}/\mathrm{d}x$ with the sub-threshold photoproduction cross section $(\sigma_A^{sub}/A)$ across four nPDF parameterizations, finding consistent linear behavior in EPPS21, nNNPDF3.0, and TUJU21 (with notable inconsistencies in light nuclei for nCTEQ15HQ), and suggesting a gluon EMC effect that varies by nucleus. It then probes the quark linear relation in proton-induced Drell–Yan, revealing strong parameterization dependence: EPPS21 and nCTEQ15HQ exhibit a clear linear relation between $-\mathrm{d}R_A^{\mathrm{DY}}/\mathrm{d}x_2$ and SRC factor $a_2(A)$, while nNNPDF3.0 shows deviations, underscoring tensions among nPDF fits. Overall, the work highlights the potential universality of SRC-driven modifications for partons while emphasizing the need for more data to reconcile different nPDF parameterizations and to solidify the EMC-SRC connection.

Abstract

In this work, we focus on the possible linear relation between short-range correlations (SRCs) and the EMC effect for partons in nuclei. First, we test a linear relationship pertaining to gluons in bound nuclei; it is manifested as a correlation between the slope of the reduced cross section ratio in deep inelastic scattering (DIS) and the cross section of sub-threshold $J/ψ$ photoproduction. For comparison, the results from four different global analyses groups of nuclear parton distribution functions (nPDFs) are utilized. These results show a good linear correlation between the gluons in bound nuclei and the slope of the reduced cross section ratio, consistent with the possible presence of nuclear effects in the gluon distributions. Second, we investigate the linear relationship of quarks in the proton-induced Drell-Yan process. The corresponding results for quarks show strong sensitivity to the parameterization forms adopted by the different groups. These findings enhance our understanding of the substructure in bound nuclei and provide valuable reference for future global fitting of nPDFs.

Figures (9)

• Figure 1: $R_A^{c \bar{c}}\left(x, Q^2\right)$ defined in Eq. (\ref{['nuclear_modi']}) as a function of $x$ by using the results of global analyses from different collaborations. The typical kinematics are chosen $Q^2= 10\,\textrm{GeV}^2$, $\sqrt{s}=20\,\textrm{GeV}$. Different colors correspond to different nuclei, as indicated by the legends.
• Figure 2: The ratio $\frac{\sigma_{A}^{sub}\!/A}{\sigma_{A'}^{sub}\!/A'}$ in Eq. (\ref{['ratioofsubcross']}) for different nuclei with respect to Carbon, at different $x$ and $Q^2$.
• Figure 3: The linear relation between the slope of nuclear modification $(-dR_A^{c \bar{c}}/dx)$ and the sub-threshold cross section $(\sigma_{A}^{sub}\!/A)$. The gluon nPDFs are adopted from different collaborations (EPPS21, nNNPDF3.0(no LHCb D), TUJU21, and nCTEQ15HQ, respectively). The black dashed lines correspond to fits of numerical results.
• Figure 4: The proton-induced Drell-Yan process at leading order.
• Figure 5: The ratio of proton-induced Drell-Yan differential cross sections as a function of $x_2$ in different nuclei, the typical kinematics are chosen $Q^2= 25\,\textrm{GeV}^2$, $\sqrt{s}=40\,\textrm{GeV}$.