The success of the ambitious programs of both long-and short-baseline neutrino-oscillation experiments employing liquid-argon time-projection chambers will greatly rely on the precision with which the weak response of the argon nucleus can be estimated. In the E12-14-012 experiment at Jefferson Lab Hall A, we studied the properties of the argon nucleus by scattering a high-quality electron beam off a high-pressure gaseous argon target. Here, we present the measured 40 Ar(e, e ) double differential cross section at incident electron energy E = 2.222 GeV and scattering angle θ = 15.54 • . The data cover a broad range of energy transfers, where quasielastic scattering and delta production are the dominant reaction mechanisms. The result for argon is compared to our previously reported cross sections for titanium and carbon, obtained in the same kinematical setup.Precise determination of charge-parity (CP) symmetry violation in the lepton sector-necessary to shed light on the matter-antimatter asymmetry in the universeis among the highest priorities of particle physics. Over the next two decades, this issue will be a primary science goal of the Deep Underground Neutrino Experiment (DUNE) [1], together with a search for proton decay, measurement of the electron-neutrino flux from a corecollapse supernova-should one occur in our galaxy during the lifetime of DUNE-and search for physics beyond the standard model.In the next few years, the Short-Baseline Neutrino (SBN) program [2] at Fermilab will provide a definitive answer to the question of the existence of sterile neutrinos, which could be the source of electron-like events recently reported with statistical significance 4.8σ by the MiniBooNE Collaboration [3].Both DUNE and the SBN program (will) employ liquid-argon time-projection chambers as their detectors, the advantages of which are low threshold momenta for particle detection and high spatial resolution, allowing (among others) for precise neutrino-energy reconstruction and distinguishing photons from electrons. As a consequence, the success of both programs in studying neutrino oscillations with unprecedented precision will greatly rely on the precision with which we understand

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A system of modular sealed gas target cells has been developed for use in electron scattering experiments at the Thomas Jefferson National Accelerator Facility (Jefferson Lab). This system was initially developed to complete the MARATHON experiment which required, among other species, tritium as a target material. Thus far, the cells have been loaded with the gas species 3 H, 3 He, 2 H, 1 H and 40 Ar and operated in nominal beam currents of up to 22.5 µA in Jefferson Lab's Hall A. While the gas density of the cells at the time of loading is known, the density of each gas varies uniquely when heated by the electron beam. To extract experimental cross sections using these cells, density dependence on beam current of each target fluid must be determined. In this study, data from measurements with several beam currents within the range of 2.5 to 22.5 µA on each target fluid are presented. Additionally, expressions for the beam current dependent fluid density of each target are developed.