Can tetraneutron be a narrow resonance?

TL;DR

This paper investigates the possibility of a narrow four-neutron resonance using advanced ab initio methods, finding that such a resonance likely has a width too large to match experimental claims, thus challenging its existence.

Contribution

The study applies novel ab initio techniques and a new resonance identification method to analyze four-neutron systems, providing a critical assessment of their resonance properties.

Findings

Four-neutron energy compatible with experiments

Resonance width exceeds experimental upper limits

Supports reaction process interpretation over resonance formation

Abstract

The search for a resonant four-neutron system has been revived thanks to the recent experimental hints reported in Phys. Rev. Lett. \textbf{116}, 052501 (2016). 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 quasi-stationary formalism using \textit{ab initio} techniques with various two-body chiral interactions. We employ the No-Core Gamow Shell Model and the 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.