Collectivization of anti-analog strength above charged particle thresholds

Abstract

Ten years ago, highly-excited states were found in 9 Li and 10 Be a few hundred kilovolts above the proton decay threshold. These physical states are too low in energy to be the isospin-stretched configuration of the decay channel (the isobaric analog or T>). However these states can be understoond by a continuum cognizant shell model as strongly mixed states of lower-isospin (T<) where the mixing is largely mediated by the open neutron channels but ushered in energy to be just above the proton threshold.

Invariant-mass spectroscopy of O14 excited states

“…To describe spectra of 14 O resonances and their properties, we used the Shell Model Embedded in the Continuum (SMEC) which describes resonances in the framework of the shell model for open quantum systems [1,2,5,25,26]. Recent SMEC applications included the study of correlations and clustering in near-threshold states [1][2][3][4] and the change of the continuum coupling strength for like and unlike nucleons in exotic nuclei [24].…”

“…13). It should be noted that in this presentation, the ET dynamics is independent of the reference state chosen for solving the fixed-point equation (4).…”

“…Clearly this advance is required to splice structure and reaction theories. Thus far, the lessons from this effort are many and include an explanation of several levels close to decay thresholds [1][2][3][4] and the demonstration of the enhanced mixing of standard shell-model eigenstates when the coupling to the continua is allowed [1,2,5]. Both of these features can destroy touchstones, like mirror symmetry, employed by nuclear physicists for decades.…”

Convenient Location of a Near-Threshold Proton-Emitting Resonance in B11

“…Arguably the most famous state of such character is the excited 0 + state of 12 C very close to the α-particle separation energy, which was postulated by Hoyle to explain production of carbon in stars [2,3]. Other examples abound [4][5][6][7]. The narrow near-threshold resonances are very important in astrophysical settings where most reactions happen at very low energies near the threshold [6].…”

Collectivity of the electromagnetic transitions in near-threshold resonances

“…Following this conjecture, the Hoyle resonance close to the α-particle emission threshold in 12 C should carry an imprint of the [ 8 Be⊕α] decay channel, whereas the 1/2 + 1 resonance of 17 O, well above the neutron emission threshold and in the vicinity of the α-particle emission threshold should carry the imprint of [ 13 C⊕α] decay channel and not of the [ 16 O⊕n] channel. Similarly, the ground state of 11 Li should resemble the [ 9 Li⊕2n] configuration of the nearest 2n-emission threshold rather than the [ 10 Li⊕n] configuration, and the collectivization of 1/2 + 6 neutron resonance in 9 Li should be caused primarily by the proximity of [ 8 He⊕p] decay channel [22].…”