1,280 research outputs found
Single spin asymmetries in inclusive high energy hadron-hadron collision processes
It has been realized for quite a long time that single-spin experiments, in
which one of the colliding objects is transversely polarized, can be helpful in
studying the properties of strong interaction in general and in testing Quantum
Chromodynamics (QCD) in particular.
Striking effects have been observed in the past few years which deviate
drastically from the expectation of the perturbative QCD parton model.
These effects have received much attention.
New experiments of the similar type are underway and/or planned.
Different theoretical attempts have been made to understand these effects.
In this review, the special role played by singly polarized high-energy
hadron-hadron collisions in High Energy Spin Physics is emphasized.
Characteristics of the available data for inclusive hadron productions are
briefly summarized.
Different theoretical approaches for such processes are reviewed with special
attention to a non-perturbative model which explicitly takes the orbital motion
of the valence quarks and hadronic surface effects into account.
The connection between such asymmetries and hyperon polarization in
unpolarized reactions is discussed.
An example of the possible application of such experimental results in other
processes is given.Comment: 62 pages, 17 ps-figures (Review article to appear in Inter. J. Mod.
Phys. A
Spin content of Lambda and its longitudinal polarization in annihilation at high energies
Longitudinal polarization of Lambda produced in annihilation at LEP
energies is calculated in a picture for the spin content of Lambda which is
consistent with the polarized deep inelastic lepton-nucleon scattering data and
SU(3) flavor symmetry for hyperon decay so that the spin of Lambda is not
completely carried by its -valence quark. A comparison with the recent ALEPH
data and the results of earlier calculations based on the static quark model in
which the spin of Lambda is completely determined by the -quark is given.
The result shows that further measurements of such polarization should provide
useful information to the question of which picture is more suitable in
describing the spin effects in the fragmentation processes.Comment: 12 pages, 2 figure
Evidence for Substantial Charge Symmetry Violation in Parton Distributions
In principle one can test the validity of charge symmetry for parton
distributions by comparing structure functions measured in neutrino and charged
lepton deep inelastic scattering. New experiments make such tests possible;
they provide rather tight upper limits on parton charge symmetry violation
[CSV] for intermediate Bjorken x, but appear to show evidence for CSV effects
at small x. We examine two effects which might account for this experimental
discrepancy: nuclear shadowing corrections for neutrinos, and strange quark
contributions s(x) unequal to sbar(x). We show that neither of these two
corrections removes the experimental discrepancy between the structure
functions. We are therefore forced to consider the possibility of a
surprisingly large CSV effect in the nucleon sea quark distributions.Comment: 10 pages, 3 postscript figure
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