Two-Neutron Halo State of ${}^{15}$B Around $3.48$ MeV By A Three-Body Model

TL;DR

This paper models the low-lying states of neutron-rich ${}^{15}$B as a three-body system, revealing a potential two-neutron halo state at around 3.61 MeV that correlates with experimental observations.

Contribution

It introduces a three-body Faddeev formalism to analyze ${}^{15}$B, identifying a new excited state with halo characteristics not previously characterized.

Findings

Discovery of a second $3/2^-$ state at 3.61 MeV

Identification of a two-neutron halo state with large matter radius

Potential correlation with experimentally observed excited state

Abstract

We investigate low-lying bound states of the neutron-rich nucleus ${}^{15}$B by assuming it is a three-body system made of an inert core ${}^{13}$B and two valence neutrons. The three-body wave functions are obtained using the Faddeev formalism. Special attention is paid to the excited state at $3.48(6)$ MeV observed in the ${}^{13}\text{C}({}^{14}\text{C},{}^{12}\text{N}){}^{15}\text{B}$ reaction, whose properties are less clear theoretically. In our three-body model, besides the ground state $3/2_1^-$, a second $3/2_2^-$ state is discovered at around $3.61$ MeV, which might be identified with the excited state observed at $3.48(6)$ MeV. We study this $3/2_2^-$ state in detail, which turns out to be a two-neutron halo state with a large matter radius $r_\text{m}\approx 4.770$ fm.