31,290 research outputs found
The Quark Spin Distributions of the Nucleon
The quark helicity measured in polarized deep inelastic scattering is
different from the quark spin in the rest frame of the nucleon. We point out
that the quark spin distributions are connected with the
quark helicity distributions and the quark transversity
distributions by an approximate relation: . This relation will be useful in order to measure
the rest frame (or quark model) spin distributions of the nucleon once the
quark helicity distributions and quark transversity distributions are
themselves measured. We also calculate the -dependent quark transversity
distributions and quark spin distributions in
a light-cone SU(6) quark-spectator model, and present discussions on possible
effect from the sea quark-antiquark pairs.Comment: 16 latex pages including a ps figure, many changes in abstract, text
and references, Final version to appear in Phys.Lett.
Electromagnetic Form Factors of Nucleons in a Light-cone Diquark Model
We investigate the electromagnetic form factors of nucleons within a simple
relativistic quark spectator-diquark model using the light-cone formalism.
Melosh rotations are applied to both quark and vector diquark. It is shown that
the difference between vector and scalar spectator diquarks reproduces the
right electric form factor of neutrons, and both the form factors
and of the proton and neutron agree with experimental data well up
to in this simple model.Comment: 16 pages, Revtex4, minor changes, to appear in Phys. Rev.
Understanding the proton spin "puzzle" with a new "minimal" quark model
We investigate the spin structure of the nucleon in an extended Jaffe-Lipkin
quark model. In addition to the conventional structure, different
admixtures in the nucleon wavefunction are also taken into
account. The contributions to the nucleon spin from various components of the
nucleon wavefunction are discussed. The effect due to the Melosh-Wigner
rotation is also studied. It is shown that the Jaffe-Lipkin term is only
important when antiquarks are negatively polarized. We arrive at a new
"minimal" quark model, which is close to the naive quark model, in order to
understand the proton spin "puzzle".Comment: 19 latex pages, Published in Eur.Phys.J.
Nucleon Transversity Distribution from Azimuthal Spin Asymmetry in Pion Electroproduction
The azimuthal asymmetry observed by the HERMES collaboration in
semi-inclusive pion production in deep inelastic scattering of unpolarized
positron on the longitudinally polarized proton target, can provide information
of the quark transversity distributions of the nucleon. We show that the quark
transversity distributions predicted both by the light-cone
quark-spectator-diquark model and by a pQCD inspired model can give consistent
descriptions of the available HERMES data for the analyzing powers
and for and
productions. We also show that the two models give similar predictions of
for production, whereas they give very different
predictions of for production at large .
Further precision measurement of for production
can provide a decisive test of different models.Comment: 11 latex pages, 1 figure, version to appear in PR
The Flavor and Spin Structure of Hyperons from Quark Fragmentation
We systematically study the hadron longitudinal polarizations of the octet
baryons at large from quark fragmentations in -annihilation,
polarized charged lepton deep inelastic scattering (DIS) process, and neutrino
(antineutrino) DIS process, based on predictions of quark distributions for the
octet baryons in the SU(6) quark-spectator-diquark model and a perturbative QCD
based counting rule analysis. We show that the -annihilation and
polarized charged lepton DIS process are able to distinguish between the two
different predictions of the hyperon polarizations. We also find that the
neutrino/antineutrino DIS process is ideal in order to study both the valence
content of the hyperons and the antiquark to hyperon (quark to anti-hyperon)
fragmentations, which might be related to the sea content of hyperons.Comment: 32 latex pages, 11 figures, a misprint in Table 1 corrected,
reference updated, to appear in PR
, Polarization and Spin Transfer in Lepton Deep-Inelastic Scattering
The flavor and helicity distributions of the and
hyperons for both valence and sea quarks are calculated in a perturbative QCD
(pQCD) based model. We relate these quark distributions to the fragmentation
functions of the and , and calculate the
-dependence of the longitudinal spin transfer to the and
in lepton deep-inelastic scattering (DIS). It is shown that the
spin transfer to the is compatible with the first HERMES results at
DESY and further tests are suggested. We also make predictions for the
-dependence of the and longitudinal polarizations
in neutrino (antineutrino) DIS processes. We investigate the sea contribution
to the fragmentation functions, and we test a possible scenario where sea
quarks in (or sea antiquarks in ) are negatively
polarized, whereas sea antiquarks in the (or sea quarks in
) are positively polarized. The asymmetry of the polarized
fragmentation functions of sea quarks and antiquarks to and
provides a way to understand the different behaviour between
the and spin transfers observed in the recent E665
experiment at FNAL.Comment: 23 latex pages, 5 figures, references added to the last version, to
appear in Eur. Phys. J.
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