97,536 research outputs found

    Influence of the Dirac sea on proton electromagnetic knockout

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    We use the relativistic distorted-wave impulse approximation (RDWIA) to study the effects of negative-energy components of Dirac wave functions on the left-right asymmetry for (e,e'p) reactions on 16-O with 0.2 < Q^2 < 0.8 and 12-C with 0.6 < Q^2 < 1.8 (GeV/c)^2. Spinor distortion is more important for the bound state than for the ejectile and the net effect decreases with Q^2. Spinor distortion breaks Godon equivalence and the data favor the CC2 operator with intermediate coupling to the sea. The left-right asymmetry for Q^2 < 1.2 (GeV/c)^2 is described well by RDWIA calcuations, but at Q^2 = 1.8 (GeV/c)^2 the observed variation with missing momentum is flatter than predicted.Comment: 12 pages, 9 figures, to be submitted to PR

    RDWIA analysis of 12C(e,e'p) for Q^2 < 2 (GeV/c)^2

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    We analyze data for 12C(e,e'p) with Q^2 < 2 (GeV/c)^2 using the relativistic distorted-wave impulse approximation (RDWIA) based upon Dirac-Hartree wave functions. The 1p normalization extracted from data for Q^2 > 0.6 (GeV/c)^2 is approximately 0.87, independent of Q^2, which is consistent with the predicted depletion by short-range correlations. The total 1p and 1s strength for E_m < 80 MeV approaches 100% of IPSM, consistent with a continuum contribution for 30 < E_m < 80 MeV of about 12% of IPSM. Similarly, a scale factor of 1.12 brings RDWIA calculations into good agreement with 12C(e,e'p) data for transparency. We also analyzed low Q^2 data from which a recent NDWIA analysis suggested that spectroscopic factors might depend strongly upon the resolution of the probe. We find that momentum distributions for their empirical Woods-Saxon wave functions fit to low Q^2 data for parallel kinematics are too narrow to reproduce data for quasiperpendicular kinematics, especially for larger Q^2, and are partly responsible for reducing fitted normalization factors.Comment: 19 pages, 14 figures, to be submitted to PR

    Atom-atom ionization mechanism in Argon-Xenon mixtures

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    The atom-atom ionization process occurring in high-purity argon-xenon mixtures has been investigated by means of a conventional shock tube employing a microwave probe to monitor the electron-generation rate. All tests were conducted at approximately atmospheric pressure and at temperatures in the range between 5000° and 9000°K, corresponding to a neutral-particle density of 7.0 X 10^(17) cm^(-3). The cross-sectional slope constant for xenon ionized by collision with an argon atom is 1.8 X 10^(-20) cm^2/eV±20%, that is, equal to that for xenon ionized by collision with another xenon atom. The data for the reaction of argon ionizing xenon are consistent with an activation energy of 8.315 eV, that is, of the xenon-xenon, atom-atom ionization process. No data were obtained for xenon ionizing argon. Good correlation was obtained between the cross sections for electron elastic momentum exchange derived from the microwave experiment and those obtained from beam experiments. The argon-xenon ionization cross section implies that, for atom-atom processes in the noble gases at pressures ~ 1 atm and temperatures ~2/3 eV, the ionization cross section is independent of the electronic structure of the projectile atom

    Atom-atom ionization cross sections of the noble gases-Argon, Krypton, and Xenon

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    An experimental investigation of the initial phase of shock produced ionization in argon, krypton, and xenon has been conducted in order to elucidate the atom-atom ionization reaction and to determine the atom-atom ionization cross sections. A high-purity shock tube was employed to heat these gases to temperatures in the range from 5000° to 9000°K at neutral particle densities of 4.4 X 10^(17), 7.0 X 10^(17), and 13.3 X 10^(17) cm^(-3), and impurity levels of approximately 10^(-6) A K-band (24-GHz) microwave system situated so that the microwave-beam propagation direction was normal to the shock tube, monitored the ionization relaxation process occurring immediately after the passage of the shock front. Electron density was calculated from the microwave data using a plane-wave-plane-plasma slab interaction theory corrected for near field effects associated with the coupling of the microwave energy to the plasma. These data, adjusted to compensate for the effects of shock attenuation, verified that the dominant electron-generation process involve a two-step, atom-atom ionization reaction, the first step (excitation to the first excited states) being rate determining. The quadratic dependence on neutral density associated with this reaction was experimentally demonstrated (with an uncertainty of ± 15%). The cross section, characterized as having a constant slope from threshold (first excited energy level), represented as the cross-sectional slope constant C, was found to be equal to 1.2 X 10^(-19)±15% cm^2/eV, 1.4 X 10^(-19)±15% cm^2/eV, and 1.8 X 10^(-20)±15% cm^2/eV for argon, krypton, and xenon, respectively. The electron-atom elastic momentum-exchange cross sections derived from the microwave data correlated quite well with Maxwell-averaged beam data, the agreement for the case of argon being ±20%; krypton, ±30%; and xenon, within a factor of 2

    Naturalism in International Adjudication

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