Can Tetraneutron be a Narrow Resonance?

The search for a resonant four-neutron system has been revived thanks to the recent experimental hints reported in [1]. The existence of such a system would deeply impact our understanding of nuclear matter and requires a critical investigation. In this work, we study the existence of a four-neutron resonance in the quasistationary formalism using ab initio techniques with various two-body chiral interactions. We employ no-core Gamow shell model and density matrix renormalization group method, both supplemented by the use of natural orbitals and a new identification technique for broad resonances. We demonstrate that while the energy of the four-neutron system may be compatible with the experimental value, its width must be larger than the reported upper limit, supporting the interpretation of the experimental observation as a reaction process too short to form a nucleus.

Figure 1

Evolution of the energy and width (shaded area) of the four-neutron system with the scaling of the N3LO interaction from 2.0 to 1.0. The circles represent the NCGSM results with two neutrons in the continuum, which is used to generate the NCGSM results based on natural orbitals with two (triangles) and three (squares) neutrons in the continuum. The DMRG results without truncations are represented by stars. The experimental energy is indicated by a diamond and the gray area shows the maximal experimental uncertainties. This area is extended up to an interaction 20% more attractive to guide the reader.