Session FA: Understanding the Nuclear Interaction Across Scales

Two-nucleon correlations and the generalized contact formalism

Nuclear short-range correlations (SRCs), i.e. the probability of finding few nucleons close to each other inside the nucleus, are an integral part of the description of nuclear systems, important also for neutrons-star structure and for the bound nucleon structure function. To study the implications of such correlations, we use a new theoretical tool, called the generalized contact formalism. In this talk I will present the original contact formalism, designed for atomic systems, and our generalization to nuclear systems. Using this formalism, we have been able to identify and quantify the effects of two-body SRCs on various nuclear quantities. Among these quantities are the one-body and two-body momentum distributions and the Coulomb sum-rule. Recently, analyzing the nuclear spectral function, we were also able to utilize the contact formalism to study exclusive electron scattering experimental data, which is one of the main experimental tools for studying SRCs. Most of our predictions were verified experimentally or numerically.   

The Short range correlations in neutron-rich nuclei

Short-range correlations (SRCs) are responsible for the high-momentum tail in the nucleon momentum distribution and account for 20--25\% of the nucleons in the nucleus. Experimental results showed that the contribution of np-pairs to SRCs is around 18 times larger than that from pp or nn-pairs. This dominance is due to the tensor force in nucleon-nucleon interaction. Neutron-rich nuclei are ideal playgrounds for studying other important aspects of SRCs, such as asymmetry dependence and separated pairing probability of proton and neutron. In this talk, I will present recent results of SRCs studies using neutron-rich nuclei. I will also talk about some upcoming experiments which aim at a more comprehensive understanding of SRCs.   

Pairing Interactions in Mg-40

The study of nuclei far from stability is one of the most active and challenging areas of nuclear structure physics. One of the most exotic neutron-rich nuclei currently accessible to experiment is $^{40}$Mg, which lies at the intersection of the nucleon magic number $N$=28 and the dripline and is expected to have a large prolate deformation similar to that observed in the neighboring lighter isotopes $^{32-38}$Mg. In addition, the occupation of the weakly bound low-l p$_{3/2}$ state may lead to the appearance of an extended neutron halo. $^{40}$Mg offers an exciting possibility and a rare opportunity to investigate the coupling of weakly bound valence particles to a deformed core, and the influence of near threshold effects on collective rotational motion. \\ \\ We will discuss the results of an experiment carried out at RIBF RIKEN to study low- lying excited states in $^{40}$Mg produced by a 1-proton removal reaction from a 240 MeV/u $^{41}$Al secondary beam. Two gamma rays were observed, and the excitation spectrum shows unexpected properties compared to both neighboring Mg isotopes, and theoretical model predictions. Potential explanations for the observed structure will be speculated on, which may have interesting implications for weakly-bound nuclei across the Segre chart. \\ \\ For the NP0906-RIBF03R2 Collaboration