Session 3WEA: Multi-neutron Systems I

Experiments on 4n using SHARAQ spectrometer

Study of isolated multi-neutron systems is one of fundamental subjects in nuclear physics.  

Recentrly observed 4n mass spectrum by using alpha-knockout (KO) reaction from ⁸He shows a strong correlation just above the 4n threshold in addition to a contimuum with a broad bump structure[1], which is similar characteristics to the 4n mass spectrum obtained by using an exothermic double-charge exchange (DCX) reaction ⁴He(⁸He,⁸Be) at 190 A MeV[2].

Production mechanism and kinematical consideration for the DCX experiment are introduced, where an impulse nature and the recoil-less condition are emphasized.  The relevant reaction process populating a four-body continuum system taking into account the final-state interactions in the di-neutrons is discussed as well as differences and common natures in the KO reaction.

Results on a new DCX experiment with better accuracy in the 4n mass are also presented.

Reference:

[1] M. Duer et al., Nature 606, 678 (2022)

[2] K. Kisamori et al., Phys. Rev. Lett 116, 052501 (2016)   

Correlated 4n system: a recent experimental result using SAMURAI setup

In this talk, I will present recent, high-quality results on the tetraneutron system from a novel experiment performed at the SAMURAI setup at RIKEN. The correlation energy between four neutrons was measured following the quasi-elastic removal of the alpha cluster from ⁸He projectiles using the missing mass method. This measurement has provided for the first time a notably clean experimental signature for a possible four-neutron resonance state near threshold. The results have been recently published in Nature [2]. The quest now continues with renewed interest as theoretical models attempt to reproduce and explain the experimental result while new experiments aim to confirm and refine the result. 

[1] Marqués, F. M. & Carbonell, J. EPJ A 57, 105 (2021).

[2] Duer et al., Nature 606, 678–682 (2022)   

Theoretical calculations on multi-neutron states,

Recently, peak of exstence of 4n system has been reprorted at RIKEN near 4n breakup threshold. Motived by this report, theoretical efforts have been done.

Some theoretical results are positive, that is, 4n states should be exsited as resonant state, while some results are nagative, that is, there is no resonant states.

In this workshop, I report 4n state theoretically. Also, if there is some time, I also report on 7H system.