
Physics Letters B 743 (2015) 267–271
Contents lists available at ScienceDirect
Physics Letters B
www.elsevier.com/locate/physletb
Nuclear force and the EMC effect
Rong Wang
a,b,c,∗
, Xurong Chen
a
a
Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000, China
b
Lanzhou University, Lanzhou 730000, China
c
University of Chinese Academy of Sciences, Beijing 100049, China
a r t i c l e i n f o a b s t r a c t
Article history:
Received
22 August 2014
Received
in revised form 3 December 2014
Accepted
23 February 2015
Available
online 26 February 2015
Editor:
D.F. Geesaman
Keywords:
Nuclear
force
EMC
effect
A linear correlation is shown quantitatively between the magnitude of the EMC effect measured in
electron deep inelastic scattering (DIS) and the nuclear residual strong interaction energy (RSIE) obtained
from nuclear binding energy subtracting the Coulomb energy contribution. This phenomenological
relationship is used to extract the size of in-medium correction (IMC) effect on deuteron and to predict
the EMC slopes |dR
EMC
/dx| of various nuclei. We further investigate the correlations between RSIE and
other quantities which are related to the EMC effect. The observed correlations among RSIE, EMC slope
and SRC ratio R
2N
N
total
/N
np(
3
S
1
)
imply that the local nuclear environment drives the modification of
quark distributions.
© 2015 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license
(http://creativecommons.org/licenses/by/4.0/). Funded by SCOAP
3
.
1. Introduction
The per-nucleon structure function F
A
2
measured on a nucleus
(A > 2) was first reported to be smaller than that measured on
deuterium at intermediate x
B
(0.35 < x
B
< 0.7) by European Muon
Collaboration in 1983 [1]. This phenomenon is now commonly re-
ferred
to as the EMC effect, which was completely unexpected
before the experiment. The early expectation was that the per-
nucleon
lepton deep inelastic scattering (DIS) cross sections of
heavy nuclei would not differ much from that of deuteron, for the
nuclear binding energies are subtle compared to the high energy
lepton probes (at GeV energy scale and higher). Anyway, the quark
momentum distributions in bound nucleons embedded in nuclei
are modified. A lot of theoretical efforts have been made aimed at
understanding the underlying physics which alters the quark distri-
butions
inside nuclei. Comprehensive reviews of the EMC effect can
be found in Refs. [2–5]. However, there is no generally accepted
model for the effect over all A and x
B
.
Early
experiment at SLAC showed that the EMC effect was log-
arithmically
related to atomic mass number A, or proportional to
the average nuclear density [6]. However, recent measurement at
JLab found the assumption that the size of the EMC effect scales
with nuclear density breaks down for very light nuclei [7]. It is
suggested that the effect scales with the local nuclear environment
of the nucleons. Since then, the nuclear dependence of quark dis-
*
Corresponding author.
E-mail
address: rwang@impcas.ac.cn (R. Wang).
tributions has become an important subject to explore the origin
of the EMC effect.
Detailed
analysis of the nuclear dependence of the EMC effect
and short-range correlations (SRC) is presented in Ref. [8], aimed
at testing the possible explanations for the correlation between the
EMC effect and SRC [9]. It is suggested that the local density expla-
nation
[7,8] is slightly better than the explanation in terms of high
virtuality [9,10] by comparing the fits to EMC slopes versus a
2
and
the fits to EMC slopes versus R
2N
N
total
/N
iso
. The SRC scaling factor
a
2
= (2/A)σ
A
/σ
d
is defined as the ratio of per-nucleon inclusive
electron scattering cross section on nucleus A to that on deuteron
at Q
2
> 1.4 (GeV
2
/c
2
) and 1.5 < x
B
< 1.9 [11]. R
2N
is similar to
a
2
but with the correction for c.m. motion of the correlated pair,
which better represents the relative probability of a nucleon being
part of a short-range correlation pair [8]. The explanation for the
EMC-SRC correlation is still not clear.
As
we know, protons and neutrons inside nuclei are bound
together with nuclear force. In Quantum Chromodynamics (QCD)
theory level, the powerful attractive nuclear force comes from the
residual strong interaction of quarks, which resembles the Van der
Waals force between molecules. The emergence of nuclear force
from QCD theory is a complex phenomenon and depends on the
distances being considered. Nonetheless, calculations of interac-
tions
among nucleons are starting to be realized from Lattice QCD
[12–14]. The nuclear medium modifies the quark distributions of
a nucleon. A related fundamental question is whether the nuclear
force plays an important role in the EMC effect.
http://dx.doi.org/10.1016/j.physletb.2015.02.059
0370-2693/
© 2015 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). Funded by
SCOAP
3
.