The CaFe Experiment: Short-Range Pairing Mechanisms in Heavy Nuclei Proposal to Je↵erson Lab PAC 44

Nucleon-nucleon short range correlated (NN SRC) pairs account for about 25% of nucleons in medium to heavy nuclei and about 75% of the nucleon’s kinetic energy. Almost all high-momentum protons in nuclei have a correlated partner and that partner is almost always a neutron. While this general outline of nucleon pairing is explained by the nucleon-nucleon tensor force, we still do not understand quantitatively the details of the pairings. To learn more, we plan to systematically study how changing the number of protons and neutrons in a nucleus changes the probability of NN SRC pairings. To do this, we will measure the (e, e0p) reaction over a range of kinematics on several nuclei: d, 12C, 40Ca, 48Ca, and 54Fe. With this data, we will be able to determine the relative probability of finding high-momentum (p > p fermi ) and low momentum (p < p fermi ) protons in each nucleus. This will allow an experimental determination of how the pairing probability changes from the lightest symmetric nucleus, d, to 12C, to a heavy symmetric nucleus 40Ca; as well as determining the pairing probabilities with 8 more neutrons by going from 40Ca to 48Ca and then by adding 6 more protons going from 48Ca to 54Fe. The eight extra neutrons in 48Ca compared to 40Ca constitute a 40% increase in the neutron number. These eight neutrons are in the 1f7/2 shell, outside the 40Ca closed shell, and are thus in very di↵erent orbitals from the protons they are expected to form pairs with. The cross sections will be measured at high Q2 and x > 1 to reduce the e↵ects of Meson Exchange Currents and Isobar Currents and in non-perpendicular kinematics to reduce the e↵ects of Final State Interactions. We will use 40 uA of 11 GeV beam in Hall-C and detect the scattered electrons in the SHMS and the knocked out protons in the HMS. We request four days of beamtime to significantly improve our quantitative understanding of nucleon pairing in nuclei.