Clustering effects for explaining an anomalous JLab result on the Be-9 structure function

TL;DR

This paper investigates whether clustering configurations in Be-9 can explain an anomalously large nuclear modification observed in JLab measurements, suggesting high-density effects due to clustering influence the structure function.

Contribution

It introduces a model separating mean and high-density contributions to nuclear structure functions, highlighting clustering effects as a possible explanation for the anomaly.

Findings

Clustering in Be-9 may explain the anomalous JLab slope.

High-density regions from clustering could modify nucleon structure.

The study suggests clustering effects are observable in high-energy nuclear reactions.

Abstract

An anomalous nuclear modification was reported by JLab measurements on the beryllium-9 structure function F_2. It is unexpected in the sense that a nuclear modification slope is too large to be expected from its average nuclear density. We investigated whether it is explained by a nuclear clustering configuration in Be-9 with two \alpha nuclei and surrounding neutron clouds. Such clustering aspects are studied by using antisymmetrized molecular dynamics (AMD) and also by a simple shell model for comparison. We consider that nuclear structure functions F_2^A consist of a mean conventional part and a remaining one depending on the maximum local density. The first mean part does not show a significant cluster effect on F_2. However, we propose that the remaining one could explain the anonymous JLab slope, and it is associated with high densities created by the cluster formation in Be-9. The JLab measurement is possibly the first signature of clustering effects in high-energy nuclear reactions. A responsible physics could be an internal nucleon modification, which is caused by the high densities due to the cluster configuration.