Nuclear Neutron-Proton Contact and the Photoabsorption Cross Section

The nuclear neutron-proton contact is introduced, generalizing Tan’s work, and evaluated from medium energy nuclear photodisintegration experiments. To this end we reformulate the quasideuteron model of nuclear photodisintegration and establish the bridge between the Levinger constant and the contact. Using experimental evaluations of Levinger’s constant, we extract the value of the neutron-proton contact in finite nuclei and in symmetric nuclear matter. Assuming isospin symmetry we propose to evaluate the neutron-neutron contact through the measurement of photonuclear spin correlated neutron-proton pairs.

Figure 1

Levinger constant values evaluated from photonuclear experiments. Red circles are based on Ref. [23], blue squares are based on Ref. [24], and green diamonds are based on Ref. [25]. Adapted with changes from Ref. [10]. The blue line shows the averaged value $L=5.50$, and the gray band its error.

Figure 2

The universal contact per particle (in units of $k_F$), measured in ultracold atoms, compared to the averaged $pn$ contact evaluated here from photonuclear experiments. Orange triangles: measurement with ultracold ${}^{40}\mathrm{K}$ atoms [3]; purple diamonds: ultracold ${}^6\mathrm{Li}$ atoms [5, 6]. Red, blue, and green dots: nuclear contact based on photonuclear experiments of Refs. [23, 24, 25]. The square’s bounds represent the experimental error for the different data sets. The line is the theoretical prediction of Ref. [6].