Cluster structure of a low-energy resonance in tetraneutron

Abstract

We theoretically investigate the possibility for a tetraneutron to exist as a low-energy resonance state. We explore a microscopic model based on the assumption that the tetraneutron can be treated as a compound system where 3 n+n and 2 n+ 2 n coupled cluster configurations coexist. The influence of the Pauli principle on the kinetic energy of the relative motion of the neutron clusters is shown to result in their attraction. The strength of such attraction is high enough to ensure the existence of a low-energy resonance in the tetraneutron, provided that the oscillator length is large enough. The first claim of the experimental observation of the nuclear stable tetraneutron has been made in [1]. Since then all other experimental attempts to find either a bound or a resonance state in the system of four neutrons have not met with success. However, in a recently reported experiment with the breakup of 14 Be [2] six events consistent with the formation of a bound tetraneutron were revealed. Unfortunately, several other experiments [3,4,5] undertaken to verify these results failed to prove or refute completely the existence of the tetraneutron due to a poor statistics. An overall conclusion of a number of theoretical papers on this subject [6,7,8,9] is that it does not seem possible to change modern nuclear Hamiltonians to bind a tetraneutron without destroying many other successful predictions of those Hamiltonians. For instance, calculations within the hyperspherical functions method (HSFM) [7] suggest that a very strong phenomenological four-nucleon force is needed in order to bind the tetraneutron. And yet neither theoretical nor experimental results exclude the possible existence of tetraneutron as a low-energy resonance (see [6,9,10]).There are only few cases of theoretical treatment of the resonant tetraneutron. In Ref.[9] the continuum states of the 4 n system were studied in the framework of the approach which combines concepts of the HSFM and the resonating-group method (RGM). Along with the lowest order hyperharmonic the authors of Ref.[9] invoked the hyperharmonics with hypermomenta K = K min + 2 and K = K min + 4, which reproduce 2 n+ 2 n clustering of the tetraneutron. The analysis of the energy behaviour of the eigenphases led authors to the conclusion that 4 n has a resonance state at an energy of about 1-3 MeV. But clear indication of such a resonance was obtained only for the Volkov effective N N potential, which is known to be inappropriate for studying multineutron systems as it binds dineutron.The most systematic study of four-neutron resonances * Electronic address: lashko@univ.kiev.ua † Electronic address: gfilippov@bitp.kiev.ua was performed in [8], where configuration space FaddeevYakubovsky equations have been solved using realistic N N interaction to follow the resonance pole trajectories in the complex energy plane. It was concluded in [8] that tetraneutron -bound or resonant -can be created only in strong external fields and would disintegrate right after such a field is removed. The sa...

Candidate Resonant Tetraneutron State Populated by theHe4(He8Kisamori1, Shimoura2, Miya3 et al. 2016Phys. Rev. Lett.16391274View full textAdd to dashboardCite

“…Another possibility of forming a resonant state is the influence of the attractive interaction due to forming a compound system, where 3 n þ n and 2 n þ 2 n coupled cluster configurations coexist, as discussed in Ref. [22]. Our result should serve as a basis for further investigations.…”

“…An investigation of a resonant state by solving the Faddeev-Yakubovsky equations with a complex energy plane shows that a resonant state can be generated only in the presence of a strong four-body force, which is incompatible with the current understanding of nuclear interactions [21]. A calculation assuming a compound system with coexisting 3 n þ n and 2 n þ 2 n coupled cluster configurations suggested the possibility of an attractive interaction to ensure the existence of a resonant state [22]. According to these calculations, the observation of a resonant tetraneutron state can significantly impact our understanding of nuclear few-body systems and nucleon-nucleon interactions.…”

Tetraneutron condensation in neutron rich matter

“…Long standing searches of this four neutron state were initiated by studying its possible formation in the break-up reaction 14 Be → 10 Be+ 4 n [1]. Despite the fact that the existence of bound tetraneutrons was theoretically excluded with high confidence [2,3,4,5,6,7,8], no arguments able to rule out the resonant 4 n state were presented. A new splash of enthusiasm to studies of the four neutron resonance is motivated by a recent experimental claim that such a state with an excitation energy E 4n = 0.83 MeV and width Γ 4n = 2.6 MeV was detected in the exchange reaction α+ 8 He → 8 Be+ 4 n [9].…”

“…Such large widths seem to indicate that tetraneutrons are not likely to exist under the form of stable aggregates although this may be possible if confined by strong external fields [2,10]. The simplest system exhibiting such a tetraneutron confinement could be associated to 8 He. In such a system, nuclear forces create a significant potential barrier which prevents the break up of tetraneutrons and confines them around α-cores.…”

Search of Trineutron and Tetraneutron

“…The existence of the bound tetraneutron system was also discussed in theoretical studies [57][58][59][60][61][62]. In Ref.…”