Lambda Polarization in Lepton Induced Reactions

Different phenomenological approaches for Lambda and Lambda-bar polarization in polarized semi-inclusive deep inelastic scattering and electron-positron annihilation at Z^0 pole are considered. Current and future experiments will soon provide accurate enough data to study spin phenomena in these reactions and distinguish between various models.Comment: LaTeX, 7 pages, 6 figures. Talk given at the SPIN-97 VII Workshop on High Energy Spin Physics, 7-12 July 1997, Dubna, Russi

Extracting the Sivers function from polarized SIDIS data and making predictions

The most recent data on the weighted transverse single spin asymmetry $A_{UT}^{\sin(\phi_h-\phi_S)}$ from HERMES and COMPASS collaborations are analysed within LO parton model with unintegrated parton distribution and fragmentation functions; all transverse motions are taken into account, with exact kinematics, in the elementary interactions. The overall quality of the data is such that, for the first time, a rather well constrained extraction of the Sivers function for $u$ and $d$ quarks is possible and is performed. Comparisons with models are made. Based on the extracted Sivers functions, predictions for $A_{UT}^{\sin(\phi_h-\phi_S)}$ asymmetries at JLab are given; suggestions for further measurements at COMPASS, with a transversely polarized hydrogen target and selecting favourable kinematical ranges, are discussed. Predictions are also presented for Single Spin Asymmetries (SSA) in Drell-Yan processes at RHIC and GSI.Comment: 18 pages, 10 figures, version published in PRD, one figure and comments adde

Transversity and Collins functions from SIDIS and e+e- data

A global analysis of the experimental data on azimuthal asymmetries in semi-inclusive deep inelastic scattering (SIDIS), from the HERMES and COMPASS Collaborations, and in e+e- --> h1 h2 X processes, from the BELLE Collaboration, is performed. It results in the extraction of the Collins fragmentation function and, for the first time, of the transversity distribution function for u and d quarks. These turn out to have opposite signs and to be sizably smaller than their positivity bounds. Predictions for the azimuthal asymmetry A_{UT}^{sin(phi_h + phi_S)}, as will soon be measured at JLab and COMPASS operating on a transversely polarized proton target, are then presented.Comment: Revised version to appear in Phys. Rev. D. Few misprints corrected, new figure

The Sivers Function from SIDIS Data

We study the Sivers effect in transverse single spin asymmetries (SSA) for pion and kaon production in Semi-Inclusive Deep Inelastic Scattering (SIDIS) processes. We perform a fit of A^{sin(phi_h-phi_S)}_UT taking into account the recent data from HERMES and COMPASS Collaborations, which allow a new determination of the Sivers distribution functions for quark and anti-quark with u, d and also s flavours. Estimates for forthcoming SIDIS experiments at COMPASS and JLab are given.Comment: 4 pages, 1 figure. To appear in the proceedings of the XVI International Workshop on Deep-Inelastic Scattering and Related Subjects, DIS 2008, London, U.K., 7-11 April 200

Predictions for double spin asymmetry A_{LT} in Semi Inclusive DIS

In the leading order of QCD parton model of Semi Inclusive Deep Inelastic Scattering (SIDIS) the double spin asymmetry $A_{LT}$ arises due to the longitudinal polarization of quarks in the transversely polarized nucleon. The corresponding $k_T^2$ weighted distribution function $g^{(1)}_{1T}$ can be related to ordinary helicity distribution $g_1(x)$ measured in DIS. Using recent parameterizations for (un)polarized distribution and fragmentation functions we calculated $A_{LT}$ asymmetry on transversely polarized proton and deuteron targets for different types hadron production. The predictions are given for COMPASS, HERMES and JLab energies. The role of Lorentz invariance relations and positivity constraints are discussed.Comment: The new conventional definition of asymmetry is adopted -- the factor two is added. The figures are rescaled by factor tw