4,178 research outputs found
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.
A platelet alpha-granule membrane protein (GMP-140) is expressed on the plasma membrane after activation.
We have previously characterized a monoclonal antibody, S12, that binds only to activated platelets (McEver, R.P., and M.N. Martin, 1984, J. Biol. Chem., 259:9799-9804). It identifies a platelet membrane protein of Mr 140,000, which we have designated as GMP-140. Using immunocytochemical techniques we have now localized this protein in unstimulated and thrombin-stimulated platelets. Polyclonal antibodies to purified GMP-140 were used to enhance the sensitivity of detection. Nonpermeabilized, unstimulated platelets, incubated with anti-GMP-140 antibodies, and then with IgG-gold probes, showed very little label for GMP-140 along their plasma membranes. In contrast, thrombin-stimulated platelets exhibited at least a 50-fold increase in the amount of label along the plasma membrane. On frozen thin sections of unstimulated platelets we observed immunogold label along the alpha-granule membranes. We also employed the more sensitive technique of permeabilizing with saponin unstimulated platelets in suspension, and then incubating the cells with polyclonal anti-GMP-140 antibodies and Fab-peroxidase conjugate. Alpha-granule membranes showed heavy reaction product, but no other intracellular organelles were specifically labeled. These results demonstrate that GMP-140 is an alpha-granule membrane protein that is expressed on the platelet plasma membrane during degranulation
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.
Phase equilibria and solidification of Mg-rich Al-Mg-Si alloys
The solidification and solid-state phase equilibria of four Al-Mg-Si alloys containing 30-70%Mg and 0.5-3.5%Si, selected on the basis of an isothermal section of the Al-Mg-Si system calculated at 300 °C, have been investigated. Solidification paths of Mg-rich Al-Mg-Si alloys finish on ternary eutectics and the temperatures of two of these eutectic reactions, i.e. L↔(Al)+β+ Mg2Si and L↔(Mg)+γ+ Mg2Si, have been determined to be at ~ 448 °C and ~ 436 °C respectively by DTA. The characteristic temperatures recorded on the DTA curves are analysed and a linear relationship is found between the peak temperature and the square root of the scanning rate
The Quark-Antiquark Asymmetry of the Nucleon Sea from and Fragmentation
We present a general analysis of the spin transfer for and
production in deep-inelastic scattering of polarized charged
leptons on the nucleon, and find that the pattern of different behaviors of
and production observed by the E665 Collaboration
suggests the possibility of quark-antiquark asymmetries either in the quark to
fragmentation functions and/or in the quark and antiquark
distributions of the target proton. We also point out that the
strange-antistrange asymmetry of the nucleon sea may produce an observable
contribution to the different behaviors of and
production. We find that a softer than as predicted by the
light-cone baryon-meson fluctuation model of intrinsic quark-antiquark pairs of
the nucleon sea might lead to a reasonable picture. However, the magnitude is
still too small to explain the E665 data and the conclusion has also strong
model-dependence. This may suggest the importance of quark-antiquark asymmetry
in the quark to fragmentation functions, provided that the E665 data
are confirmed.Comment: 15 latex pages, 2 figure
Phenomenological Relation between Distribution and Fragmentation Functions
We study the relation between the quark distribution function q(x) and the
fragmentation function D_q(z) based on a general form D_q(x) =
C(z)z^{alpha}q(z) for valence and sea quarks. By adopting two known
parametrizations of quark distributions for the proton, we find three simple
options for the fragmentation functions that can provide a good description of
the available experimental data on proton production in e^+ e^- inelastic
annihilation. These three options support the revised Gribov-Lipatov relation
D_q(z) = z q(z) at z --> 1, as an approximate relation for the connection
between distribution and fragmentation functions. The three options differ in
the sea contributions and lead to distinct predictions for antiproton
production in the reaction p+p --> p-bar+X, thus they are distinguishable in
future experiments at RHIC-BNL.Comment: 13 pages, 5 eps figure
Spin Transfers for Baryon Production in Polarized pp Collisions at RHIC-BNL
We consider the inclusive production of longitudinally polarized baryons in
collisions at RHIC-BNL, with one longitudinally polarized proton.
We study the spin transfer between the initial proton and the produced baryon
as a function of its rapidity and we elucidate its sensitivity to the quark
helicity distributions of the proton and to the polarized fragmentation
functions of the quark into the baryon. We make predictions using an SU(6)
quark spectator model and a perturbative QCD (pQCD) based model. We discuss
these different predictions, and what can be learned from them, in view of the
forthcoming experiments at RHIC-BNL.Comment: 28 pages, 11 figure
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