The Challenge of the EMC Effect: existing data and future directions

TL;DR

The paper surveys the EMC effect by compiling precise DIS data and reviewing the formalism for nuclear structure functions, including $d^{2}\sigma/(d\Omega dE')$, $F_{1,2}$, and $R=\sigma_L/\sigma_T$, with attention to L/T separation and isoscalar corrections. It compares traditional convolution, dynamical rescaling, and medium-modification theories, and discusses SRC/multi-quark cluster viewpoints, highlighting a notable correlation between the EMC slope $|dR_{EMC}/dx|$ and SRC indicators such as the high-$x$ plateau $a_2$ observed in SRC measurements. The authors outline a future experimental program—probing flavor dependence via PVDIS, SIDIS, and Drell-Yan with pions, polarized EMC, and the $R_A-R_D$ ratio—aimed at distinguishing competing mechanisms and extending measurements to new nuclei and kinematic regions. The work emphasizes that resolving the EMC effect will deepen our understanding of nuclear PDFs, QCD in the nuclear medium, and the role of high-momentum nucleons in shaping parton distributions, with wide implications for neutrino scattering and collider phenomenology.

Abstract

Since the discovery that the ratio of inclusive charged lepton (per-nucleon) cross sections from a nucleus A to the deuteron is not unity - even in deep inelastic scattering kinematics - a great deal of experimental and theoretical effort has gone into understanding the phenomenon. The EMC effect, as it is now known, shows that even in the most extreme kinematic conditions the effects of the nucleon being bound in a nucleus can not be ignored. In this paper we collect the most precise data available for various nuclear to deuteron ratios, as well as provide a commentary on the current status of the theoretical understanding of this thirty year old effect.

Figures (13)

• Figure 1: Top: Ratios of the $^3$He to Deuterium DIS cross sections. The measurements shown are from JLab Seely:2009gt (circles) and HERMES hermes_he3_n:2003 (triangles). Bottom: Ratios of the $^4$He to Deuterium DIS cross sections. The measurements shown are from JLab Seely:2009gt (circles), NMC Amaudruz:1995tq (triangles) and SLAC Gomez:1993ri (squares). In both panels the error bars represent the statistical and point-to-point systematic uncertainties added in quadrature. The bands show the fits to the combined data sets and their uncertainties when both the normalization and point-to-point errors are taken into account (see text for details).
• Figure 2: Top: Ratios of the $^6$Li to Deuterium DIS cross sections. The measurements shown are from NMC Arneodo:1995cs (triangles). Bottom: Ratios of the $^9$Be to Deuterium DIS cross sections. The measurements shown are from JLab Seely:2009gt (circles), NMC Arneodo:1996rvAmaudruz:1995tq (triangles) and SLAC Gomez:1993ri (squares). In both panels the error bars represent the statistical and point-to-point systematic uncertainties added in quadrature. The bands show the fits to the combined data sets and their uncertainties when both the normalization and point-to-point errors are taken into account (see text for details).
• Figure 3: Top: Ratios of the $^{12}$C to Deuterium DIS cross sections. The measurements shown are from JLab Seely:2009gt (circles), NMC Arneodo:1995cs (triangles), SLAC Gomez:1993ri (squares) and EMC Arneodo:1989sy (stars). Bottom: Ratios of the $^{14}$N to Deuterium DIS cross sections. The measurements shown are from HERMES hermes_he3_n:2003 (circles) and BCDMS Bari:1985ga (stars). In both panels the error bars represent the statistical and point-to-point systematic uncertainties added in quadrature. The bands show the fits to the combined data sets and their uncertainties when both the normalization and point-to-point errors are taken into account (see text for details).
• Figure 4: Top: Ratios of the $^{27}$Al to Deuterium DIS cross sections. The measurements shown are from ROCHESTER-SLAC-MIT Bodek:1983ec (circles), NMC Arneodo:1996rvAmaudruz:1995tq (triangles) and SLAC Gomez:1993ri (squares). Bottom: Ratios of the $^{40}$Ca to Deuterium DIS cross sections. The measurements shown are from EMC Arneodo:1989sy (stars), NMC Amaudruz:1995tq (triangles) and SLAC Gomez:1993ri (squares). In both panels the error bars represent the statistical and point-to-point systematic uncertainties added in quadrature. The bands show the fits to the combined data sets and their uncertainties when both the normalization and point-to-point errors are taken into account (see text for details).
• Figure 5: Top: Ratios of the $^{56}$Fe to Deuterium DIS cross sections. The measurements shown are from ROCHESTER-SLAC-MIT Bodek:1983qn (circles), NMC Arneodo:1996rvAmaudruz:1995tq (triangles), SLAC Gomez:1993ri (squares) and BCDMS Benvenuti:1987az (flipped triangles). Bottom: Ratios of the $^{64}$Cu to Deuterium DIS cross sections. The measurements shown are from EMC Ashman:1992kv (circles). In both panels the error bars represent the statistical and point-to-point systematic uncertainties added in quadrature. The bands show the fits to the combined data sets and their uncertainties when both the normalization and point-to-point errors are taken into account (see text for details).