A new variable, called the contact, was introduced recently by S. Tan for systems of two component fermions.  In our work we generalize the definition of the contact for nuclear systems and use it to study different properties of nuclei, such as short-range correlations and photo-nuclear reactions.

In ultra cold atomic systems, Tan's contact measures the probability to find two atoms close together and is connected to many properties of the system, such as its energy, pressure and the high momentum tail of the momentum distribution of the atoms. These relations were proved both experimentally and theoretically.

The aim of our work is to generalize the definition of the contact to nuclear systems and to use it for finding new and interesting relations between nuclear quantities. So far we have successfully defined the matrices of nuclear contacts and connected them to both the quasi-deuteron (qd) photo-disintegration model and to the high momentum tail of the nucleon momentum distributions. In the generalized definition of the contact, we have taken into consideration all partial waves and finite-range interactions. Regarding the photo-disintegration, we have reformulated Levinger's qd model, resulting a relation between the Levinger constant and the nuclear neutron-proton contacts. For the high momentum tails, we have obtained relations between the contacts and the one-nucleon and the two-nucleon momentum distributions. As a result, we have obtained an asymptotic relation between these two momentum distributions. This relation emphasizes the important contribution of two-body short-range correlations to the high momentum tail and was verified using available Variational Monte Carlo numerical data. Using this numerical data we have also obtained a very good correspondence between our two independent relations (the qd relation and the momentum relations). The numerical data was also used to study more properties of the nuclear contacts, including their scaling along the nuclear chart.

The nuclear contacts seem to become a useful tool for studying different properties of nuclear systems. In future works we plan on expanding the contact relations to more aspects of nuclear systems.

References:

1. R. Weiss, B. Bazak and N. Barnea, Phys. Rev. Lett. 114, 012501 (2015).
2. R. Weiss, B. Bazak and N. Barnea, Phys. Rev. C (accepted for publication, arXiv: 1503.07047 [nucl-th])