The dominance of the $\nu(0d_{5/2})^2$ configuration in the $N=8$ shell in $^{12}$Be from the breakup reaction on a proton target at intermediate energy

TL;DR

This study investigates the neutron shell structure of $^{12}$Be through proton-induced breakup reactions, revealing a dominant $ u(0d_{5/2})^2$ configuration in its ground state via momentum distribution analysis.

Contribution

It provides experimental evidence for the dominance of the neutron $ u(0d_{5/2})^2$ configuration in $^{12}$Be, using DWIA analysis of breakup reactions at intermediate energy.

Findings

Strong contribution of neutron $0d_{5/2}$ orbital in $^{12}$Be

Spectroscopic factor for $0d_{5/2}$ is 1.39(10)

Dominance of $ u(0d_{5/2})^2$ configuration in ground state

Abstract

The momentum distribution of $^{11}$Be fragments produced by the breakup of $^{12}$Be interacting with a proton target at 700.5 MeV/$u$ energy has been measured at GSI Darmstadt. To obtain the structure information on the anomaly of the $N=8$ neutron shell, the momentum distribution of $^{11}$Be fragments from the one-neutron knockout $^{12}$Be(p,pn) reaction, measured in inverse kinematics, has been analysed in the distorted wave impulse approximation (DWIA) based on a quasi-free scattering scenario. The DWIA analysis shows a surprisingly strong contribution of the neutron $0d_{5/2}$ orbital in $^{12}$Be to the transverse momentum distribution of the $^{11}$Be fragments. The single-neutron $0d_{5/2}$ spectroscopic factor deduced from the present knock-out data is 1.39(10), which is significantly larger than that deduced recently from data of $^{12}$Be breakup on a carbon target. This result provides a strong experimental evidence for the dominance of the neutron $\nu(0d_{5/2})^2$ configuration in the ground state of $^{12}$Be.