The challenge of the EMC effect: Existing data and future directions

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.

Measurement of PromptD-Meson Production inp−PbCollisions atsNAbelev1, Adam2, Adamová3 et al. 2014Phys. Rev. Lett.984480View full textAdd to dashboardCite

“…A complete understanding of the Pb-Pb results requires an understanding of cold-nuclear-matter effects in the initial and final states, which can be accessed by studying p-Pb collisions assuming that the QGP is not formed in these collisions. In the initial state, the nuclear environment affects the quark and gluon distributions, which are modified in bound nucleons depending on the parton fractional momentum x and the atomic mass number A [11,12]. At LHC energies, the most relevant effect is gluon saturation at low x, which can modify the D-meson production significantly at low p T .…”

PDFs from protons to nuclei

“…The former nuclei are more strongly bound, and the nuclear deformation of their parton distributions are the subject of nPDF fits. Intermediate between these, are the so-called "light" ions, that exhibit characteristics of both classes and not necessarily can be extrapolated from the behavior of either, as has become increasingly evident thanks in particular to recent high precision measurements at Jefferson Lab [48,49,50,51]. Much more data on DIS on light and heavy nuclei is expected from Jefferson Lab's 12 GeV upgrade [5,6], as well as from the Electron-Ion Collider project that has just been endorsed in the NSAC long range plan released in October [5,6].…”

Probing nuclear gluons with heavy flavors at an Electron-Ion Collider

“…Distinct dynamical mechanisms are expected to cause nuclear modifications in different regions of x: modified single-nucleon structure and non-nucleonic degrees of freedom in nuclei (x > 0.3), exchange interactions between nucleons (x ∼ 0.1, antishadowing), and the appearance of coherent gluon fields associated with multiple nucleons (x < 0.01, shadowing) [1]. 1 Suppression of the nuclear quark densities in the valence region x > 0.3 has been observed in inclusive DIS (EMC effect) and is the object of intense theoretical study [2]. Some information on nuclear sea quarks is available from dilepton production.…”