Session U11: Invited Session: Correlated Fermions in Nuclei and Ultra-Cold Atomic Gasses

The nuclear contact and the photoabsorption cross section

A few years ago, S. Tan suggested that the properties of universal quantum gases depend on a new characteristic quantity. This quantity, the contact, describes the probability of two particles coming close to each other, i.e. it is a measure of the number of close particle pairs in the system. Utilizing the contact, this theory predicts the energy, pressure and other properties of the system. It was proven right in a series of ultracold atomic experiments. In my talk I will present a generalization of Tan's contact to nuclear systems, introducing the various nuclear contacts, taking into account all possible pair configurations. The leading neutron-proton contact is then evaluated from medium energy photodisintegration experiments. To this end, the Levinger quasi-deuteron model of nuclear photodisintegration is reformulated, and the bridge between the Levinger constant and the contact is established. Using experimental evaluations of Levinger's constant the value of the neutron-proton contact in finite nuclei and in symmetric nuclear matter is extracted, and compared to the universal theory. Assuming isospin symmetry it is proposed to evaluate the neutron-neutron contact through measurement of photonuclear spin correlated neutron-proton pairs.   

Possible Universal Properties of Correlated High Momentum Fermions

We discuss theoretical implications of the recent experimental observation of the dominance of tensor interaction in the $\sim$250-600 MeV/c momentum range of nucleons in the nuclei. Based on this observation we predicted two new properties for high-momentum distribution of nucleons in asymmetric nuclei which may have significant impact on the dynamical structure of the high density asymmetric nuclear matter. Another prediction is based on the observation that NN correlations in the above mentioned momentum range interact at much shorter distances than the average interaction in the nucleus. We demonstrate how this condition can lead to the phenomenon of contact in atomic nuclei. Finally, we discuss universality of our observations for any two-component fermi systems that contain short range interaction between unlike components and discuss examples ranging from cold atoms to QCD.   

Correlated Fermions from Ultra-Cold Atomic Gases to Nuclear Matter

Even in heavy neutron-rich nuclei, electron-induced nucleon knockout measurements show high momentum nucleons predominantly belong to short-range correlated neutron-proton pairs. Despite a 20-order of magnitude difference in density, the strength and shape of this high-momentum distribution are remarkably similar to those of ultra-cold atomic gases of two different fermions which can be described by Tan's contact. Furthermore, in neutron-rich nuclei, protons have a greater probability than neutrons to have momentum greater than the Fermi momentum. This has wide ranging implications from the nuclear symmetry energy to quark distributions in nuclei.