Many-channel microscopic cluster model of ${}^8$Be. I. Formation of high-energy resonance states

Abstract

The nature and structure of high-energy resonance states in ${}^8$Be, located just below and above the $p{+}^7$Li threshold, are investigated in detail. A microscopic many-cluster and many-channel model is employed to study the formation of these resonances. This model includes three distinct three-cluster configurations: ${}^4$He+${}^3$H+$p$, ${}^4$He+${}^3$He+$n$, and ${}^4$He+$d$+$d$, enabling a comprehensive treatment of all major binary decay channels of ${}^8$Be, namely ${}^4$He+${}^4$He, $p{+}^7$Li, $n{+}^7$Be, and $d{+}^6$Li. The primary focus of our analysis is the structure and dominant decay channels of the twin $1^{+}$, $2^{+}$, $3^{+}$, and $4^{+}$ resonance states. Additionally, we propose and implement a model to clarify how the $2^{+}$ resonance states lying below the $p{+}^7$Li threshold are formed. We demonstrate that these resonances are Feshbach-type states arising due to coupling of the open ${}^4$He+${}^4$He channel with the closed channels $p{+}^7$Li, $n{+}^7$Be, and $d{+}^6$Li at these energies. Overall, the present approach provides a realistic description of the experimentally observed resonance spectrum near the ${}^7$Li+$p$ decay threshold, including negative-parity states $1^{-}$ and $2^{-}$. Our results are consistent with other microscopic calculations but offer more detailed insight into the internal structure and decay pathways of these resonances.

Comments: 37 pages, 11 figures, 10 tables