First evidence for the J$>$1 components of the pygmy dipole resonance in neutron-rich nuclei

Abstract

Gamma (${\hat{I}}^3$) decay shapes the synthesis of heavy elements in neutron-rich nuclear environments of neutron star mergers, supplying the Universe with heavy elements. The low-energy pygmy dipole resonance (PDR) influences nuclear reaction rates of the rapid nucleosynthesis through enhanced ${\hat{I}}^3$ transitions. However, since it is difficult to reproduce astrophysical conditions in laboratories, PDR was previously observed only in $J=1$ spin states. Here we report the first experimental observation of $J>1$ components of PDR, identified in the ${\hat{I}}^2$-delayed ${\hat{I}}^3$ decay of the J${}^{\ddot{I}}€$ = 3${}^{-}$ spin-parity isomer of ${}^{80}$Ga. The data analysis, combined with decay information and theoretical calculations allows the identification of resonant structures below the neutron emission threshold of the neutron-rich germanium ${}^{80}$Ge as J${}^{\ddot{I}}€=(2,3{)}^{-}$ components of the PDR built on the low-lying J${}^{\ddot{I}}€$ = 2${}^{+}$ quadrupole state. Our findings extend the concept of PDR beyond dipole states, with implications for nuclear structure theory and experiment, as well as the element production in the cosmos.