Photon parton distributions in nuclei and the EMC effect

Abstract

Photons as well as quarks and gluons are constituents of the infinite momentum frame (IMF) wave function of an energetic particle. They are mostly equivalent photons whose amplitude follows from the Lorentz transformation of the particle rest frame Coulomb field into the IMF and from the conservation of the electromagnetic current. We evaluate in a model independent way the dominant photon contribution \propto α_{em}(Z^2/A^{4/3})\ln(1/R_{A}m_{N}x) to the nuclear structure functions as well as the term \propto α_{em}Z/A. In addition we show that the definition of x consistent with the exact kinematics of eA scattering (with exact sum rules) works in the same direction as the nucleus field of equivalent photons. Combined, these effects account for the bulk of the EMC effect for x\le 0.5 where Fermi motion effects are small. In particular for these x the hadronic mechanism contribution to the EMC effect does not exceed \sim 3% for all nuclei. Also the A-dependence of the hadronic mechanism of the EMC effect for x > 0.5 is significantly modified.

14 pages, 3 figures, final version published in Phys.Rev. C

References in corpus (6)

• The Physics of Ultraperipheral Collisions at the LHC
• New measurements of the EMC effect in very light nuclei
• Update of Parton Distributions at NNLO
• The Polarized and Unpolarized Photon Content of the Nucleon
• On the dependence of the wave function of a bound nucleon on its momentum and the EMC effect
• Coherent QCD phenomena in the Coherent Pion-Nucleon and Pion-Nucleus Production of Two Jets at High Relative Momenta

Cited by in corpus (5)

• Leading twist nuclear shadowing phenomena in hard processes with nuclei
• Transition between nuclear and quark-gluon descriptions of hadrons and light nuclei
• Measurement of the EMC effect in light and heavy nuclei
• QCD and QED dynamics of the EMC effect
• EMC effect, short-range nuclear correlations, neutron stars