345 research outputs found
Including Cahn and Sivers effects into event generators
It is demonstrated that event generators LEPTO and PYTHIA can be modified to
describe some azimuthal modulations. The comparisons of results obtained with
modified LEPTO with existing data in the current fragmentation region of SIDIS
are presented for Cahn and Sivers effects as well as the predictions for the
target fragmentation region. The predictions for Sivers effect in the
Drell--Yan process obtained with modified PYTHIA are also presented. The
concept of hadronization function is discussed.Comment: Presented at Transversity 2005 workshop, September 7-10, Como, Italy.
8 pages. Word Scientific Proceedings style (included
Double spin azimuthal asymmetries A_{LT} and A_{LL} in semi-inclusive DIS
Within the LO QCD parton model of SIDIS with unintegrated quark distribution
and fragmentation functions we study the transverse momentum and azimuthal
dependencies of the double spin asymmetries and . For later we
include kinematic corrections, which induce an
azimuthal modulation of the asymmetry, analogous to the Cahn effect in
unpolarized SIDIS. We show that a study of these asymmetries allows to extract
the transverse momentum dependence of the unintegrated helicity distribution
function and .
This report is based on research published in [1] and [2], where predictions
are given for ongoing COMPASS, HERMES and JLab experiments.Comment: 4 pages, 2 figures. Talk presented at the 17th International Spin
Physics Symposium, SPIN2006, Kyoto, Japan, October 2-7, 200
Lambda and Lambda-bar Polarization in Lepton Induced Processes
The study of the longitudinal polarization of Lambda and Lambda-bar hyperons
produced in polarized deep inelastic scattering, neutrino scattering, and in Z0
decays allows to access the spin dynamics of the quark fragmentation process.
Different phenomenological spin transfer mechanisms are considered and
predictions for the Lambda and Lambda-bar longitudinal polarization in various
processes using unpolarized and polarized targets are made. Current and future
semi-inclusive deep inelastic scattering experiments will provide soon accurate
enough data to study these phenomena and distinguish between various models for
the spin transfer mechanisms.Comment: 17 pages, LaTex with epsfig.sty, including 10 figures One reference
adde
Gluon Polarization from Correlated High-p_T Hadron Pairs in Polarized l - N Scattering
We propose to access the gluon polarization by measuring the cross
section spin-asymmetry in semi-inclusive polarized lepton -- nucleon
scattering. The photon-gluon fusion sub-process will be tagged by detecting
high- correlated hadron pairs in the forward hemisphere. Selecting
oppositely charged kaon pairs will allow to suppress the background coming from
gluon radiation.Comment: 6 pages, 3 eps figures, aipproc.cls and aipproc.sty include
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
Transverse spin dependent azimuthal asymmetries at COMPASS
In semi-inclusive deep inelastic scattering of polarized leptons on a
transversely polarized target eight target transverse spin-dependent azimuthal
modulations are allowed. In the QCD parton model half of these asymmetries can
be interpreted within the leading order approach and the other four are
twist-three contributions. The first two leading twist asymmetries extracted by
HERMES and COMPASS experiments are related: one to the transversity
distribution and the Collins effect, the other to the Sivers distribution
function. These results triggered a lot of interest in the past few years and
allowed the first extractions of the transversity and the Sivers distribution
functions of nucleon. The remaining six asymmetries were obtained by the
COMPASS experiment using a 160 GeV/c longitudinally polarized muon beam and
transversely polarized deuteron and proton targets. Here we review preliminary
results from COMPASS proton data of 2007.Comment: 5 pages, 4 figures, Proceedings of SPIN2010 international symposium,
J\"ulich, Germany, September 27 - October 2, 201
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
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