We have carried out an (e,e'p) experiment at high momentum transfer and in parallel kinematics to measure the strength of the nuclear spectral function S(k,E) at high nucleon momenta k and large ...removal energies E. This strength is related to the presence of short-range and tensor correlations, and was known hitherto only indirectly and with considerable uncertainty from the lack of strength in the independent-particle region. This experiment locates by direct measurement the correlated strength predicted by theory.
The influence of nuclear isospin mixing on parity-violating elastic electron scattering is studied for the even–even,
N
=
Z
nuclei
12C,
24Mg,
28Si, and
32S. Their ground-state wave functions have ...been obtained using a self-consistent axially-symmetric mean-field approximation with density-dependent effective two-body Skyrme interactions. Some differences from previous shell-model calculations appear for the isovector Coulomb form factors which play a role in determining the parity-violating asymmetry. To gain an understanding of how these differences arise, the results have been expanded in a spherical harmonic oscillator basis. Results are obtained not only within the plane-wave Born approximation, but also using the distorted-wave Born approximation for comparison with potential future experimental studies of parity-violating electron scattering. To this end, for each nucleus the focus is placed on kinematic ranges where the signal (isospin-mixing effects on the parity-violating asymmetry) and the experimental figure-of-merit are maximized. Strangeness contributions to the asymmetry are also briefly discussed, since they and the isospin mixing contributions may play comparable roles for the nuclei being studied at the low momentum transfers of interest in the present work.
We have extracted QCD matrix elements from our data on doubly polarized inelastic scattering of electrons on nuclei. We find the higher twist matrix element d˜2, which arises strictly from ...quark-gluon interactions, to be unambiguously nonzero. The data also reveal an isospin dependence of higher twist effects if we assume that the Burkhardt-Cottingham sum rule is valid. The fundamental Bjorken sum rule obtained from the a0 matrix element is satisfied at our low momentum transfer.
We have examined the spin structure of the proton in the region of the nucleon resonances (1.085 GeV<W<1.910 GeV) at an average four momentum transfer of Q2=1.3 GeV2. Using the Jefferson Lab ...polarized electron beam, a spectrometer, and a polarized solid target, we measured the asymmetries A|| and A(perpendicular) to high precision, and extracted the asymmetries A1 and A2, and the spin structure functions g1 and g2. We found a notably nonzero A(perpendicular), significant contributions from higher-twist effects, and only weak support for polarized quark-hadron duality.
Recent data from experiment E97-006 at TJNAF using the 12C(e,e′p) reaction at very large missing energies and momenta are compared with a calculation of two-step rescattering. A comparison between ...parallel and perpendicular kinematics suggests that the effects of final state interactions can be strongly reduced in the former case.
A high-precision polarimeter Hauger, M.; Honegger, A.; Jourdan, J. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
04/2001, Letnik:
462, Številka:
3
Journal Article
Recenzirano
Odprti dostop
We have built a polarimeter in order to measure the electron beam polarization in hall C at JLAB. Using a superconducting solenoid to drive the pure-iron target foil into saturation, and a ...symmetrical setup to detect the M
øller electrons in coincidence, we achieve an accuracy of <1%. This sets a new standard for M
øller polarimeters.
Changes in the nuclear charge radii of lithium isotopes were determined using a combination of precise isotope shift measurements and theoretical atomic structure calculations. We discuss the choice ...of the reference isotope for absolute charge radii determinations in the lithium isotopic chain and report a new value for the charge radius of {sup 6}Li, based on the analysis of the world scattering data. A summary of the lithium nuclear charge radii obtained in this way is presented. Additionally, new calculations in fermionic molecular dynamics for the lithium isotopes were performed. We summarize the status of the lithium nuclear charge radii, magnetic dipole and electric quadrupole moments from experimental investigations and compare them to the results of various microscopic and three-body nuclear models.
The recoil proton polarization has been measured in the p(e-->,e'p-->)pi(0) reaction in parallel kinematics around W = 1232 MeV, Q2 = 0.121 (GeV/c)2, and epsilon = 0.718 using the polarized cw ...electron beam of the Mainz Microtron. All three proton polarization components, Px/P(e) = (-11.4+/-1.3+/-1.4)%, P(y) = (-43.1+/-1.3+/-2.2)%, and P(z)/P(e) = (56.2+/-1.5+/-2.6)%, could be measured simultaneously. The Coulomb quadrupole to magnetic dipole ratio, CMR = (-6.4+/-0.7(stat)+/-0.8(syst))%, was determined from Px in the framework of the Mainz Unitary Isobar Model. The consistency among the reduced polarizations and the extraction of the ratio of longitudinal-to-transverse response is discussed.
We analyze parity-violating elastic electron scattering as a complementary tool for precise determination of neutron densities in nuclei. In particular we discuss how to extract the ratio between ...neutron and proton rms radii and monopole form factors from theoretical and experimental asymmetries. The structure of the nuclear target is obtained from a Skyrme Hartree-Fock mean field with pairing interactions in BCS approximation. We focus on the parity-violation asymmetry for 208Pb and for 12C as examples of N > Z and N Z nuclei. In the latter case we study the influence of nuclear isospin mixing by means of the asymmetry deviation. Distorted wave calculations are shown and are compared to plane wave impulse approximation.
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