High-resolution spectroscopy of exotic nuclei to study NN and 3N interactions

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The atomic nucleus is a quantum many-body system, where protons and neutrons are subject to complex NN interactions that include central, spin-orbit, tensor and many-body (e.g. 3N) contributions. The modification of nuclear structure in exotic nuclei is driven by specific components of these NN interactions and by studying experimentally very exotic nuclei, we can identify which component is responsible for distinct features of exotic nuclei. The study of these phenomena requires measurement of key spectroscopic information on excited states of exotic nuclei, and the new HiCARI campaign at RIKEN provides an exciting opportunity to do so in nuclei at the extremes of nuclear stability. In particular, we will study the lifetime of the 2+ excited state of the very neutron-rich 20C nuclide, where tensor and two-body spin-orbit forces are responsible for the erosion of the Z=6 spin-orbit shell gap. At the same time, lifetimes of excited states are very sensitive to 3N forces and such measurements at the dripline will give us a unique insight on how 3N correlations drive the shell evolution at the extremes of isospin. We will perform detailed spectroscopy of 78Ni, whose doubly magic nature has been confirmed [Nature 569, 53 (2019)]; these results, however, show a potential deformed state lying close to the spherical one, signaling a modification of nuclear structure beyond 78Ni. We will measure for the first time lifetimes in neutron-rich Ca isotopes, a critical testing ground for phenomenology and ab initio calculations, where we will be able to shed light into 3N force effects. We will measure lifetimes of excited states in the heaviest accessible N=Z nuclei 88Ru and 86Tc to shed light on the role of a special type of neutron-proton pairing correlation (isoscalar) predicted to exist in these exotic systems and which is predicted to impact on these measurements.