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

An anomalous nuclear modification was reported by JLab measurements on the beryllium‐9 structure function $F2.$ 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 $9Be$ with two α 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 $F2A$ 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 $F2.$ However, we propose that the remaining one could explain the anomalous JLab slope, and it is associated with high densities created by the cluster formation in $9Be.$ 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.