Probing nuclear forces at the extreme of isospin: the⁷H resonance

Abstract

EPN 41/2 23 t has been observed that,in these systems,nuclear forces manifest themselves in different ways.is is interpreted presently as an isospin dependence, and is questioning our understanding of the behaviour of nuclear matter going from proton-rich to neutron-rich matter. e description of nuclear forces in these weakly bound nuclear systems represents an enormous challenge. e interaction between nucleons is responsible for the creation of particular structures. e study of these structures, at the limit of nuclear binding and beyond,where non-perturbative phenomena become important, is a unique source of information."Ab initio" calculations illustrate nicely these non-perturbative phenomena. ese calculations start from interactions describing perfectly a large body of nucleon-nucleon scattering data and then solve, without further approximation, the nuclear n-body problem. However, they fail completely in reproducing macroscopic observables as, for example, nuclear binding energies (see figure 1) [1]. ese large discrepancies are attributed to the importance of 3-body forces: the interaction between two nucleons is modified by the presence of a third nucleon. non-perturbative phenomena in nuclear physicsWe can explain nuclear interaction in terms of virtual pion exchange between two nucleons. is exchange may, for example, result in an excitation of the Δ-resonance [unstable nuclear state defined by a mean energy value (E R ) and a given width (Γ R ), determined by its half-life (dt) due to the relation Γ R .dt = ħ] of one of the nucleons that interacts in this excited state with a 3 rd nucleon present in the nuclei. is last interaction can be seen as a higher order correction of the original interaction of the first two nucleons. e importance of this higher order correction is not due to the strength associated with the interaction but to its intrinsic nature. Properties of very strong Coulomb interaction have been tested in the Mott-scattering of Pb+Pb [2]. e Coulomb potential energy in this system is of the order of 500 MeV, one order of magnitude higher than the binding energy of the systems of figure 1. However, in this particular case higher order corrections, such as vacuum polarization, are only of the order of 10

Active targets for the study of nuclei far from stability

“…This experiment illustrates the unique feature of active target-TPCs to detect very low energy particles by adjusting the pressure of the detector gas. A discussion of this result can be found, too, in ''Probing nuclear forces at the extreme of isospin: the 7 H resonance'' [43]. This resonance has been observed and characterized, even if statistics were low, only 7 events.…”