Session K11: Hadronic Physics IV

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Historically, effective theories are needed to study the complex structure of the atomic nucleus. Most of these theories describe the low-momentum part of the nucleon momentum distribution well. However, they fail to describe two-nucleon short-range correlations (SRC), which determine the behavior of approximately 20\% of nucleons in the nucleus. Contact interaction is an effective theory developed for the study of the high-momentum behavior of dilute ultra-cold two-component atomic gases. Even though nuclei don't fully satisfy the conditions of this theory, there is experimental evidence that shows it can be applied to nuclear systems. Here, we extract nuclear contacts from 2-body momentum distributions. We compare the contact-derived distributions to 1-body momentum distributions in the region sensitive to SRC, and to experimental data. We then discuss applications of this formalism to the extraction of nuclear correlation functions by combining the short and long distance nucleon behaviors using a blending function. We find that the correlation function isospin dependence comes solely from SRC. We argue that this model can be used to calculate neutrinoless double beta decay matrix elements for nuclei lacking ab initio calculations.   

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In a classical view, the nucleon-nucleon potential has a strong repulsive core. When the separation distance of a two-nucleon (sub)system is small, they will strongly repel and move away from each with large momentum. In electron Quasi-elastic (QE) scattering, these so-called short-range correlation (SRC) pairs in nuclei produce events with nucleon initial momentum above the Fermi level.\\ Previous coincidence QE measurements reported a neutron-proton pair dominance in high-momentum nucleons. Experiment E12-11-112 at JLab will check this isospin dependence of SRC by taking the ratio of 3H to 3He cross section at $Q^2>1.4 GeV^2$,and $1.5< xbj<2$ where high-momentum nucleons dominate. The first run period (December 2017) measured $^3H$, $^3He$, and $^2H$ QE cross sections with a $2.2GeV$ electron beam at $Q^2=0.4$ and $0.6 GeV^2$. This data set is under analysis for target study and neutron magnetic form factor extraction. In October 2018, the second run period will investigate SRCs in the QE tail region ($xbj > 1.5$) with $Q^2 > 1.4 GeV^2$.\\ In this talk I will describe the measurements and provide an update on our preparation for the second SRC run period.   

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Hall A at Jefferson Lab has developed a new closed gas target system for the safe use of a tritium target. The system has been used in the 12 GeV era of experiments of the Continuous Electron Beam Accelerator Facility (CEBAF) using $^{3}H$, $^{3}He$, $^{2}H$, $^{1}H$ and $^{40}Ar$, at a maximum beam current of $22.5$ $\mu A$, during 2017 and 2018. The target cells were machined from solid aluminum blocks and are all 25 cm long by 1.3 cm, with approximately 0.25 mm windows for the beam entrance and exit. While the fill density is known, the density of the gas when heated by the electron beam needs to be studied in order to calculate the correct cross sections from the experiments. As expected from simulations, we find the density of the target dependent on the current of the electron beam going through the cell. A summary of the target system and the results of the study of the density change in each one of the targets will be presented.