Sprecher
Beschreibung
The advanced beam delivery at HIE-ISOLDE (CERN), combined with the high-resolution, high-efficiency MINIBALL $\gamma$-ray spectrometer, enables precision measurements of electromagnetic observables involving high-lying excited states, thereby providing stringent tests of modern nuclear theory. Such measurements were pioneered at TRIUMF [1,2]. Nuclei such as $^{12}$C, $^{24}$Mg and $^{48}$Ca constitute ideal benchmark systems, as electromagnetic observables including transition probabilities, dipole polarizabilities, and spectroscopic quadrupole moments can be measured with high precision and calculated within state-of-the-art theoretical frameworks, including the no-core shell model (NCSM), nuclear lattice effective field theory (NLEFT), and the projected generator coordinate method (PGCM) for $^{12}$C and $^{24}$Mg, and coupled-cluster (CC) theory for $^{48}$Ca. Here we present the nuclear-structure science case for these nuclei by combining new experimental and theoretical results with a proposal for precision low-energy Coulomb-excitation measurements — i.e., well below the Coulomb barrier — at HIE-ISOLDE. Specifically, we present compelling cases for the study of the nuclear dipole polarizability and the spectroscopic quadrupole moments of the first excited J=2$^+$ states. Both observables arise as second-order effects in Coulomb-excitation perturbation theory and may compete with one another in light nuclei [3]. To date, the nuclear dipole polarizability of a first excited state has not been measured in any even-even nucleus.
In addition, we will present the motivation for investigating the nuclear shapes and collective properties of the heavier benchmark nuclei $^{76}$Ge-$^{86}$Kr and $^{136}$Xe-$^{136}$Ba, including shape fluctuations, shape coexistence and triaxial rotation. Coulomb-excitation measurements of these nuclei are potentially feasible at HIE-ISOLDE and, together with the powerful MINIBALL array, provide a unique opportunity to elucidate the role of deformation in shaping proton–neutron correlations. A more detailed science case will be presented at this workshop. Following discussion at the workshop and within the HIE-ISOLDE community, these studies will form the foundation of a broader research programme on benchmark nuclei, culminating in Expressions of Interest to the INTC.
References
[1] Orce, Drake, Navratil et al, Phys. Rev. C (R) (2012).
[2] Kumar Raju, Orce, Navratil et al., Phys. Lett. B (2018).
[3] Orce, IJMP E (2020).