316 research outputs found
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
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 and quarks is possible and is performed.
Comparisons with models are made. Based on the extracted Sivers functions,
predictions for 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 arises due to the
longitudinal polarization of quarks in the transversely polarized nucleon. The
corresponding weighted distribution function can be
related to ordinary helicity distribution measured in DIS. Using
recent parameterizations for (un)polarized distribution and fragmentation
functions we calculated 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
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