Measurement of the Nucleon Structure Function F2 in the Nuclear Medium and Evaluation of its Moments

Abstract

We report on the measurement of inclusive electron scattering off a carbon target performed with CLAS at Jefferson Laboratory. A combination of three different beam energies 1.161, 2.261 and 4.461 GeV allowed us to reach an invariant mass of the final-state hadronic system W ≈ 2.4 GeV with four-momentum transfers Q 2 ranging from 0.2 to 5 (GeV/c) 2 . These data, together with previous measurements of the inclusive electron scattering off proton and deuteron, which cover a similar continuous two-dimensional region of Q 2 and Bjorken variable x, permit the study of nuclear modifications of the nucleon structure. By using these, as well as other world data, we evaluated the F 2 structure function and its moments. Using an OPE-based twist expansion, we studied the Q 2 -evolution of the moments, obtaining a separation of the leading-twist and the total higher-twist terms. The carbon-to-deuteron ratio of the leading-twist contributions to the F 2 moments exhibits the well known EMC effect, compatible with that discovered previously in x-space. The total higher-twist term in the carbon nucleus appears, although with large systematic uncertainties, to be smaller with respect to the deuteron case for n < 7, suggesting partial parton deconfinement in nuclear matter. We speculate that the spatial extension of the nucleon is changed when it is immersed in the nuclear medium.

Higher twist in electroproduction: Flavor nonsinglet QCD evolution

“…A large fraction of this data [5][6][7][8][9][10][11] is on the proton structure function F p 2 (x, Q 2 ) which is now the best measured quantity in deep inelastic electron scattering. Data is also available on deuterium [12] and heavy nuclear [13] targets in the high-x and low Q 2 region. The data on the structure functions in the resonance region has been compared to the scaling curves obtained from global fits [14,15] of the PDFs and DGLAP evolution.…”