The Flavor and Spin Structure of Hyperons from Quark Fragmentation

We systematically study the hadron longitudinal polarizations of the octet baryons at large $z$ from quark fragmentations in $e^+e^-$-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 $e^+e^-$-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

Λ\Lambda, Λˉ\bar{\Lambda} Polarization and Spin Transfer in Lepton Deep-Inelastic Scattering

The flavor and helicity distributions of the $\Lambda$ and $\bar{\Lambda}$ 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 $\Lambda$ and $\bar{\Lambda}$, and calculate the $z$-dependence of the longitudinal spin transfer to the $\Lambda$ and $\bar{\Lambda}$ in lepton deep-inelastic scattering (DIS). It is shown that the spin transfer to the $\Lambda$ is compatible with the first HERMES results at DESY and further tests are suggested. We also make predictions for the $z$-dependence of the $\Lambda$ and $\bar{\Lambda}$ 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 $\Lambda$ (or sea antiquarks in $\bar{\Lambda}$) are negatively polarized, whereas sea antiquarks in the $\Lambda$ (or sea quarks in $\bar{\Lambda}$) are positively polarized. The asymmetry of the polarized fragmentation functions of sea quarks and antiquarks to $\Lambda$ and $\bar{\Lambda}$ provides a way to understand the different behaviour between the $\Lambda$ and $\bar{\Lambda}$ 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 $\Delta q_{RF}(x)$ are connected with the quark helicity distributions $\Delta q(x)$ and the quark transversity distributions $\delta q(x)$ by an approximate relation: $\Delta q_{RF}(x) + \Delta q(x)=2 \delta q(x)$. 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 $x$-dependent quark transversity distributions $\delta q(x)$ and quark spin distributions $\Delta q_{RF}(x)$ 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 Λ\Lambda and Λˉ\bar{\Lambda} Fragmentation

We present a general analysis of the spin transfer for $\Lambda$ and $\bar{\Lambda}$ production in deep-inelastic scattering of polarized charged leptons on the nucleon, and find that the pattern of different behaviors of $\Lambda$ and $\bar{\Lambda}$ production observed by the E665 Collaboration suggests the possibility of quark-antiquark asymmetries either in the quark to $\Lambda$ 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 $\Lambda$ and $\bar{\Lambda}$ production. We find that a softer $\bar{s}(x)$ than $s(x)$ 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 $\Lambda$ 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 ${\vec p}p$ 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