Pairing in the continuum: the quadrupole response of the Borromean nucleus 6He

TL;DR

This paper models the ground and continuum states of 6He using a shell model with continuum p-states and pairing interactions, successfully reproducing experimental quadrupole resonance features.

Contribution

It introduces a shell model approach incorporating continuum states and pairing interactions to analyze 6He, highlighting its Borromean nature and quadrupole response.

Findings

Reproduces narrow 2+ resonance in quadrupole strength

Identifies a second wider resonance at 3.9 MeV

Provides insight into 6He structure and excitations

Abstract

The ground state and low-lying continuum states of 6He are found within a shell model scheme, in a basis of two-particle states built out of continuum p-states of the unbound 5He nucleus, using a simple pairing contact-delta interaction. This accounts for the Borromean character of the bound ground state, revealing its composition. We investigate the quadrupole response of the system and we put our calculations into perspective with the latest experimental results. The calculated quadrupole strength distribution reproduces the narrow 2+ resonance, while a second wider peak is found at about 3.9 MeV above the g.s. energy.