983 research outputs found
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
Production mechanisms and single-spin asymmetry for kaons in high energy hadron-hadron collisions
Direct consequences on kaon production of the picture proposed in a recent
Letter and subsequent publications are discussed. Further evidence supporting
the proposed picture is obtained. Comparison with the data for the inclusive
cross sections in unpolarized reactions is made. Quantitative results for the
left-right asymmetry in single-spin processes are presented.Comment: 10 pages, 2 Postscript figure
Precise Determination of Electroweak Parameters in Neutrino-Nucleon Scattering
A systematic error in the extraction of from nuclear deep
inelastic scattering of neutrinos and antineutrinos arises from higher-twist
effects arising from nuclear shadowing. We explain that these effects cause a
correction to the results of the recently reported significant deviation from
the Standard Model that is potentially as large as the deviation claimed, and
of a sign that cannot be determined without an extremely careful study of the
data set used to model the input parton distribution functions.Comment: 3pages, 0 figures, version to be published by IJMP
Lambda Polarization in Polarized Proton-Proton Collisions at RHIC
We discuss Lambda polarization in semi-inclusive proton-proton collisions,
with one of the protons longitudinally polarized. The hyperfine interaction
responsible for the - and - mass splittings gives
rise to flavor asymmetric fragmentation functions and to sizable polarized
non-strange fragmentation functions. We predict large positive Lambda
polarization in polarized proton-proton collisions at large rapidities of the
produced Lambda, while other models, based on SU(3) flavor symmetric
fragmentation functions, predict zero or negative Lambda polarization. The
effect of and decays is also discussed. Forthcoming
experiments at RHIC will be able to differentiate between these predictions.Comment: 18 pages, 5 figure
Tracing the origin of the single-spin asymmetries observed in inclusive hadron production processes at high energies
It is pointed out that the existing models for the left-right asymmetries
observed in single-spin inclusive hadron production processes can be
differentiated experimentally. Several such experiments are proposed with which
the basic assumptions of these models can be tested individually.Comment: 12 pages, one figur
Single spin asymmetries in QCD
Measurements of single transverse spin asymmetries in high energy inclusive
processes have always shown unexpected and challenging results. Several cases
are considered and discussed within a QCD approach which couples perturbative
dynamics to new non perturbative partonic information; the aim is that of
developing a consistent phenomenological description of these unusual single
spin phenomena, based on a generalized QCD factorization scheme.Comment: 14 pages, lectures delivered at School on "Symmetries and Spin",
Praha-SPIN-2001, Prague, July 15 - July 28, 200
First record of terrestrial Enchytraeidae (Annelida: Clitellata) in Versailles palace's park, France
France can be qualified as terra incognita regarding terrestrial enchytraeids because very little data has been recorded so far in this country. In spring and autumn 2016, enchytraeid communities were investigated in a loamy soil in a meadow located in the park of Versailles palace, France. In total, twenty four enchytraeid species were identified, belonging to six different genera i.e. eleven Fridericia species, four Enchytraeus species, four Achaeta species, two Buchholzia species, two Marionina species and one Enchytronia species. According to the published data, this was one of the highest diversity found in a meadow in Europe
Charge symmetry violation in the parton distributions of the nucleon
We point out that charge symmetry violation in both the valence and sea quark
distributions of the nucleon has a non-perturbative source. We calculate this
non-perturbative charge symmetry violation using the meson cloud model, which
has earlier been successfully applied to both the study of SU(2) flavour
asymmetry in the nucleon sea and quark-antiquark asymmetry in the nucleon. We
find that the charge symmetry violation in the valence quark distribution is
well below 1%, which is consistent with most low energy tests but significantly
smaller than the quark model prediction about 5%-10%. Our prediction for the
charge symmetry violation in the sea quark distribution is also much smaller
than the quark model calculation.Comment: RevTex, 26 pages, 6 PostScript figure
Analyzing powers in inclusive pion production at high energy and the nucleon spin structure
Analyzing powers in inclusive pion production in high energy transversely
polarized proton-proton collisions are studied theoretically in the framework
of the quark recombination model. Calculations by assuming the SU(6)
spin-flavor symmetry for the nucleon structure disagree with the experiments.
We solve this difficulty by taking into account the %We overcome this
difficulty by taking into account the realistic spin distribution functions of
the nucleon, which differs from the SU(6) expectation at large , %but
coincides with a perturbative QCD constraint on the ratio of the unpolarized
valence distributions, as . We also discuss the kaon spin
asymmetry and find in the polarized proton-proton
collisions at large .Comment: 13 pages, 4 figures, late
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