198 research outputs found
Parity-violating asymmetry of bosons produced in - collisions
The parity-violating asymmetry is an ideal tool to study the quark helicity
distribution in the proton. We study the parity-violating asymmetry of
bosons produced by longitudinally polarized - collision in
RHIC, based on predictions of quark distributions of the proton in the SU(6)
quark-spectator-diquark model and a perturbative QCD based counting rule
analysis. We find that the two models give nearly equal asymmetry for but
that for quite different. Therefore future experiments on such quantity
can help to clarify different predictions of the value at in the proton.Comment: 11 Latex pages, 9 figures, final version to appear in NP
Target mass corrections and twist-3 in the nucleon spin structure functions
The Nachtmann moment is employed to study the contribution of twist-3
operator to the nucleon spin structure functions. Target mass corrections to
the Cornwall-Norton moments of the spin structure functions are
discussed. It is found that the corrections play a sizeable role to the
contribution of the twist-3 extracted from the Cornwall-Norton
moments.Comment: 11 pages, 1 figure
On the Q^2 Dependence of Measured Polarized Structure Funtions
We analyse the available data on the polarized asymmetries for proton,
neutron and deuteron targets. We use a homogeneous and updated set of
unpolarized structure functions to derive from , and we accurately
correct for the scaling violations in order to obtain with the
same for all values. The contribution to the evolution of a
possible large gluon polarized density is also considered. The implications for
the Ellis-Jaffe and for the Bjorken sum rules are discussed.Comment: 11 pages (LaTex) + 4 figures (topdrawer, included at the end) CERN-TH
7023/9
Spin-dependent Parton Distributions from Polarized Structure Function Data
In the past year, polarized deep inelastic scattering experiments at CERN and
SLAC have obtained structure function measurements off proton, neutron and
deuteron targets at a level of precision never before achieved. The
measurements can be used to test the Bjorken and Ellis-Jaffe sum rules, and
also to obtain information on the parton distributions in polarized nucleons.
We perform a global leading-order QCD fit to the proton deep inelastic data in
order to extract the spin-dependent parton distributions. By using parametric
forms which are consistent with theoretical expectations at large and small
, we find that the quark distributions are now rather well constrained. We
assume that there is no significant intrinsic polarization of the strange quark
sea. The data are then consistent with a modest amount of the proton's spin
carried by the gluon, although the shape of the gluon distribution is not well
constrained, and several qualitatively different shapes are suggested. The
spin-dependent distributions we obtain can be used as input to phenomenological
studies for future polarized hadron-hadron and lepton-hadron colliders.Comment: 23 pages, DTP/94/3
The nucleon's octet axial-charge g_A^8 with chiral corrections
The value of the nucleon's flavour-singlet axial-charge extracted from
polarised deep inelastic scattering is sensitive to the value of the octet
axial-charge g_A^8 which is usually taken from an analysis of hyperon
beta-decays within the framework of SU(3) symmetry, namely 0.58 \pm 0.03. Using
the Cloudy Bag model we find that the value of g_A^8 is reduced by as much as
20% below the usual phenomenological value. This increases the value of the
flavour singlet axial charge (g_A^0|_inv) derived from deep inelastic data and
significantly reduces the difference between it and g_A^8.Comment: 12 page
Analytic Approaches to the Evolution of Polarised Parton Distributions at Small
The evolution of polarised parton distributions at small is
studied. Various analytic approximations are critically discussed. We compare
the full evolution with that obtained from the leading-pole approximation to
the splitting functions, and show that the validity of this approximation
depends critically on the behaviour of the starting distributions. A
new analytic solution which is valid at small is obtained, and its domain
of applicability is discussed.Comment: 14 pages, LATeX, 4 figures availabe as .uu-fil
Nucleon quark distributions in a covariant quark-diquark model
Spin-dependent and spin-independent quark light-cone momentum distributions
and structure functions are calculated for the nucleon. We utilize a modified
Nambu-Jona-Lasinio model in which confinement is simulated by eliminating
unphysical thresholds for nucleon decay into quarks. The nucleon bound state is
obtained by solving the Faddeev equation in the quark-diquark approximation,
where both scalar and axial-vector diquark channels are included. We find
excellent agreement between our model results and empirical data.Comment: 6 pages, 7 figure
Valence Quark Spin Distribution Functions
The hyperfine interactions of the constituent quark model provide a natural
explanation for many nucleon properties, including the Delta-N splitting, the
charge radius of the neutron, and the observation that the proton's quark
distribution function ratio d(x)/u(x)->0 as x->1. The hyperfine-perturbed quark
model also makes predictions for the nucleon spin-dependent distribution
functions. Precision measurements of the resulting asymmetries A_1^p(x) and
A_1^n(x) in the valence region can test this model and thereby the hypothesis
that the valence quark spin distributions are "normal".Comment: 16 pages, 2 Postscript figure
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