Clustering aspects in nuclear structure functions

TL;DR

This paper investigates how nuclear clustering in light nuclei like Be-9 influences deep inelastic scattering structure functions, suggesting clustering effects may explain observed anomalies beyond traditional models.

Contribution

It demonstrates that clustering structures in nuclei can impact structure functions and may explain anomalies not accounted for by simple shell models.

Findings

Clustering affects high-momentum components in nuclear wave functions.

Nuclear modifications of F_2 are similar in AMD and shell models, with slight differences in Be-9.

Clustering structures can explain the Be-9 anomaly via high-density regions.

Abstract

For understanding an anomalous nuclear effect experimentally observed for the beryllium-9 nucleus at the Thomas Jefferson National Accelerator Facility (JLab), clustering aspects are studied in structure functions of deep inelastic lepton-nucleus scattering by using momentum distributions calculated in antisymmetrized (or fermionic) molecular dynamics (AMD) and also in a simple shell model for comparison. According to the AMD, the Be-9 nucleus consists of two alpha-like clusters with a surrounding neutron. The clustering produces high-momentum components in nuclear wave functions, which affects nuclear modifications of the structure functions. We investigated whether clustering features could appear in the structure function F_2 of Be-9 along with studies for other light nuclei. We found that nuclear modifications of F_2 are similar in both AMD and shell models within our simple convolution description although there are slight differences in Be-9. It indicates that the anomalous Be-9 result should be explained by a different mechanism from the nuclear binding and Fermi motion. If nuclear-modification slopes d(F_2^A/F_2^D)/dx are shown by the maximum local densities, the Be-9 anomaly can be explained by the AMD picture, namely by the clustering structure, whereas it certainly cannot be described in the simple shell model. This fact suggests that the large nuclear modification in Be-9 should be explained by large densities in the clusters. For example, internal nucleon structure could be modified in the high-density clusters. The clustering aspect of nuclear structure functions is an unexplored topic which is interesting for future investigations.