1,945 research outputs found
Investigation of the Neutron Form Factors by Inclusive Quasi-Elastic Scattering of Polarized Electrons off Polarized He: A Theoretical Overview
The theory of quasi-elastic inclusive scattering of polarized leptons off
polarized He is critically reviewed and the origin of different expressions
for the polarized nuclear response function appearing in the literature is
explained. The sensitivity of the longitudinal asymmetry upon the neutron form
factors is thoroughly investigated and the role played by the polarization
angle for minimizing the proton contribution is illustrated.Comment: Phys. Rev C in press; 9 figs. (available upon request
New determinations of gamma-ray line intensities of the Ep = 550 keV and Ep = 1747 keV resonances of the 13-C(p,gamma)14-N reaction
Gamma-ray angular distributions for the resonances at Ep = 550 keV and 1747
keV of the radiative capture reaction 13-C(p,g)14-N have been measured, using
intense proton beams on isotopically pure 13-C targets. Relative intensities
for the strongest transitions were extracted with an accuracy of typically five
per cent, making these resonances new useful gamma-ray standards for efficiency
calibration in the energy range Egamma = 1.6 to 9 MeV.Comment: 17 pages, 6 figures, Nuclear Instruments and Methods, Sec. A,
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Comparison of Relativistic Nucleon-Nucleon Interactions
We investigate the difference between those relativistic models based on
interpreting a realistic nucleon-nucleon interaction as a perturbation of the
square of a relativistic mass operator and those models that use the method of
Kamada and Gl\"ockle to construct an equivalent interaction to add to the
relativistic mass operator. Although both models reproduce the phase shifts and
binding energy of the corresponding non-relativistic model, they are not
scattering equivalent. The example of elastic electron-deuteron scattering in
the one-photon-exchange approximation is used to study the sensitivity of
three-body observables to these choices. Our conclusion is that the differences
in the predictions of the two models can be understood in terms of the
different ways in which the relativistic and non-relativistic -matrices are
related. We argue that the mass squared method is consistent with conventional
procedures used to fit the Lorentz-invariant cross section as a function of the
laboratory energy.Comment: Revtex 13 pages, 5 figures, corrected some typo
On the Nucleon Distribution Amplitude: The Heterotic Solution
We present a new nucleon distribution amplitude which amalgamates features of
the Chernyak-Ogloblin-Zhitnitsky model with those of the Gari-Stefanis model.
This "heterotic" solution provides the possibility to have asymptotically a
small ratio \hbox{}, while fulfilling
most of the sum-rule requirements up to the third order. Using this nucleon
distribution amplitude we calculate the electromagnetic and weak nucleon form
factors, the transition form factor and the decay widths
of the charmonium levels , , and into .
The agreement with the available data is remarkable in all cases.Comment: 15 pages, RUB-TPII-21/92 Preprin
The P_33(1232) resonance contribution into the amplitudes M_{1+}^{3/2},E_{1+}^{3/2},S_{1+}^{3/2} from an analysis of the p(e,e'p)\pi^0 data at Q^2 = 2.8, 3.2, and 4 (GeV/c)^2 within dispersion relation approach
Within the fixed-t dispersion relation approach we have analysed the TJNAF
and DESY data on the exclusive p(e,e'p)\pi^0 reaction in order to find the
P_{33}(1232) resonance contribution into the multipole amplitudes
M_{1+}^{3/2},E_{1+}^{3/2},S_{1+}^{3/2}. As an input for the resonance and
nonresonance contributions into these amplitudes the earlier obtained solutions
of the integral equations which follow from dispersion relations are used. The
obtained values of the ratio E2/M1 for the \gamma^* N \to P_{33}(1232)
transition are: 0.039\pm 0.029, 0.121\pm 0.032, 0.04\pm 0.031 for Q^2= 2.8,
3.2, and 4 (GeV/c)^2, respectively. The comparison with the data at low Q^2
shows that there is no evidence for the presence of the visible pQCD
contribution into the transition \gamma N \to P_{33}(1232) at Q^2=3-4 GeV^2.
The ratio S_{1+}^{3/2}/M_{1+}^{3/2} for the resonance parts of multipoles is:
-0.049\pm 0.029, -0.099\pm 0.041, -0.085\pm 0.021 for Q^2= 2.8, 3.2, and 4
(GeV/c)^2, respectively. Our results for the transverse form factor G_T(Q^2) of
the \gamma^* N \to P_{33}(1232) transition are lower than the values obtained
from the inclusive data. With increasing Q^2, Q^4G_T(Q^2) decreases, so there
is no evidence for the presence of the pQCD contribution here too
Nucleon electromagnetic form factors and polarization observables in space-like and time-like regions
We perform a global analysis of the experimental data of the electromagnetic
nucleon form factors, in space-like and time-like regions. We give the
expressions of the observables in annihilation processes, such as , or , in terms of form factors. We discuss some
of the phenomenological models proposed in the literature for the space-like
region, and consider their analytical continuation to the time-like region.
After determining the parameters through a fit on the available data, we give
predictions for the observables which will be experimentally accessible with
large statistics, polarized annihilation reactions.Comment: 25 pages, 5 figures 7 table
Point-Form Analysis of Elastic Deuteron Form Factors
Point-form relativistic quantum mechanics is applied to elastic
electron-deuteron scattering. The deuteron is modeled using relativistic
interactions that are scattering-equivalent to the nonrelativistic Argonne
and Reid '93 interactions. A point-form spectator approximation (PFSA)
is introduced to define a conserved covariant current in terms of
single-nucleon form factors. The PFSA is shown to provide an accurate
description of data up to momentum transfers of 0.5 , but falls
below the data at higher momentum transfers. Results are sensitive to the
nucleon form factor parameterization chosen, particularly to the neutron
electric form factor.Comment: RevTex, 31 pages, 1 table, 13 figure
Parity-Violating Electron-Deuteron Scattering
The longitudinal asymmetry due to exchange is calculated in
quasi-elastic electron-deuteron scattering at momentum transfers GeV relevant for the SAMPLE experiment. The deuteron and
scattering-state wave functions are obtained from solutions of a Schr\"odinger
equation with the Argonne potential. Electromagnetic and weak neutral
one- and two-nucleon currents are included in the calculation. The two-nucleon
currents of pion range are shown to be identical to those derived in Chiral
Perturbation Theory. The results indicate that two-body contributions to the
asymmetry are small ( 0.2%) around the quasi-elastic peak, but become
relatively more significant ( 3%) in the high-energy wing of the
quasi-elastic peak.Comment: 23 pages, 10 figure
Effect of recent R_p and R_n measurements on extended Gari-Krumpelmann model fits to nucleon electromagnetic form factors
The Gari-Krumpelmann (GK) models of nucleon electromagnetic form factors, in
which the rho, omega, and phi vector meson pole contributions evolve at high
momentum transfer to conform to the predictions of perturbative QCD (pQCD), was
recently extended to include the width of the rho meson by substituting the
result of dispersion relations for the pole and the addition of rho' (1450)
isovector vector meson pole. This extended model was shown to produce a good
overall fit to all the available nucleon electromagnetic form factor (emff)
data. Since then new polarization data shows that the electric to magnetic
ratios R_p and R_n obtained are not consistent with the older G_{Ep} and G_{En}
data in their range of momentum transfer. The model is further extended to
include the omega' (1419) isoscalar vector meson pole. It is found that while
this GKex cannot simultaneously fit the new R_p and the old G_{En} data, it can
fit the new R_p and R_n well simultaneously. An excellent fit to all the
remaining data is obtained when the inconsistent G_{Ep} and G_{En} is omitted.
The model predictions are shown up to momentum transfer squared, Q^2, of 8
GeV^2/c^2.Comment: 14 pages, 8 figures, using RevTeX4; email correspondence to
[email protected] ; minor typos corrected, figures added, conclusions
extende
Lattice Calculation of the Strangeness Magnetic Moment of the Nucleon
We report on a lattice QCD calculation of the strangeness magnetic moment of
the nucleon. Our result is . The sea contributions
from the u and d quarks are about 80% larger. However, they cancel to a large
extent due to their electric charges, resulting in a smaller net sea
contribution of to the nucleon magnetic moment. As
far as the neutron to proton magnetic moment ratio is concerned, this sea
contribution tends to cancel out the cloud-quark effect from the Z-graphs and
result in a ratio of which is close to the SU(6) relation and
the experiment. The strangeness Sachs electric mean-square radius
is found to be small and negative and the total sea contributes substantially
to the neutron electric form factor.Comment: 10 pages, 5 figures, LaTex, UK/97-23, ADP-97-55/T28
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