223 research outputs found
Perspectives in Polarized Leptoproduction
We discuss specific observables that can be measured in deep inelastic
leptoproduction in the case of 1-particle inclusive measurements, namely
azimuthal asymmetries and power-suppressed (higher twist) corrections. These
quantities contain information on the intrinsic transverse momentum of partons,
with close connection to the gluon dynamics in hadrons.Comment: 10 pages with figures, LaTex, uses espcrc1.sty and epsfig.sty.
Invited talk at the workshop on The Structure of the Nucleon (NUCLEON99),
Frascati, June 7-9, 199
Spin Measurements in lp -> hX Deep Inelastic Scattering
The production of hadrons in polarized lepton-nucleon deep inelastic
scattering is discussed. The helicity density matrix of the hadron is computed
within the QCD hard scattering formalism and its elements are shown to yield
information on the spin structure of the nucleon and the spin dependence of the
quark fragmentation process. The case of vector mesons is considered in
more detail and estimates are given.Comment: 3 pages, LaTeX, no figures. Talk delivered by J. Hansson at the XII
International Symposium on High Energy Spin Physics, Amsterdam, Sept. 10-14,
1996. To be published in the proceeding
Transverse parton momenta in single inclusive hadron production in annihilation processes
We study the transverse momentum distributions of single inclusive hadron
production in annihilation processes. Although the only
available experimental data are scarce and quite old, we find that the
fundamental features of transverse momentum dependent (TMD) evolution,
historically addressed in Drell-Yan processes and, more recently, in
Semi-inclusive deep inelastic scattering processes, are visible in annihilations as well. Interesting effects related to its non-perturbative
regime can be observed. We test two different parameterizations for the
dependence of the cross section: the usual Gaussian distribution and
a power-law model. We find the latter to be more appropriate in describing this
particular set of experimental data, over a relatively large range of
values. We use this model to map some of the features of the data within the
framework of TMD evolution, and discuss the caveats of this and other possible
interpretations, related to the one-dimensional nature of the available
experimental data
A strategy towards the extraction of the Sivers function with TMD evolution
The QCD evolution of the unpolarized Transverse Momentum Dependent (TMD)
distribution functions and of the Sivers functions have been discussed in
recent papers. Following such results we reconsider previous extractions of the
Sivers functions from semi-inclusive deep inelastic scattering data and propose
a simple strategy which allows to take into account the Q^2 dependence of the
TMDs in comparison with experimental findings. A clear evidence of the
phenomenological success of the TMD evolution equations is given, mostly, by
the newest COMPASS data off a transversely polarized proton target.Comment: 15 pages, 7 figures, 2 table
Single spin asymmetries in inclusive hadron production from SIDIS to hadronic collisions: universality and phenomenology
In a perturbative QCD approach, with inclusion of spin and transverse
momentum effects, experimental data on azimuthal asymmetries observed in
polarized semi-inclusive deeply inelastic scattering and e+ e- annihilations
can be used to determine the Sivers, transversity and Collins soft functions.
By using these functions, within the same scheme, we predict p(transv.
polarized) p -> h + X single spin asymmetries in remarkable agreement with RHIC
experimental data.Comment: 5 pages, 6 ps figure
A study on the interplay between perturbative QCD and CSS/TMD formalism in SIDIS processes
We study the Semi-Inclusive Deep Inelastic Scattering (SIDIS) cross section
as a function of the transverse momentum, . In order to describe it over a
wide region of , soft gluon resummation has to be performed. Here we will
use the original Collins-Soper-Sterman (CSS) formalism; however, the same
procedure would hold within the improved Transverse Momentum Dependent (TMD)
framework. We study the matching between the region where fixed order
perturbative QCD can successfully be applied and the region where soft gluon
resummation is necessary. We find that the commonly used prescription of
matching through the so-called Y-factor cannot be applied in the SIDIS
kinematical configurations we examine. In particular, the non-perturbative
component of the resummed cross section turns out to play a crucial role and
should not be overlooked even at relatively high energies. Moreover, the
perturbative expansion of the resummed cross section in the matching region is
not as reliable as it is usually believed and its treatment requires special
attention.Comment: Two references and an appendix added, 22 pages, 11 figure
A phenomenological analysis of azimuthal asymmetries in unpolarized semi-inclusive deep inelastic scattering
We present a phenomenological analysis of the cos-phi and cos-2phi
asymmetries in unpolarized semi-inclusive deep inelastic scattering, based on
the recent multidimensional data released by the COMPASS and HERMES
Collaborations. In the TMD framework, valid at relatively low transverse
momenta, these asymmetries arise from intrinsic transverse momentum and
transverse spin effects, and from their correlations. The role of the Cahn and
Boer-Mulders effects in both azimuthal moments is explored up to order 1/Q. As
the kinematics of the present experiments is dominated by the low-Q^2 region,
higher-twist contributions turn out to be important, affecting the results of
our fits.Comment: 18 pages, 5 figures, one paragraph added at the end of Section IV,
one reference added. PRD versio
Unpolarised Transverse Momentum Dependent Distribution and Fragmentation Functions from SIDIS Multiplicities
The unpolarised transverse momentum dependent distribution and fragmentation
functions are extracted from HERMES and COMPASS experimental measurements of
SIDIS multiplicities for charged hadron production. The data are grouped into
independent bins of the kinematical variables, in which the TMD factorisation
is expected to hold. A simple factorised functional form of the TMDs is
adopted, with a Gaussian dependence on the intrinsic transverse momentum, which
turns out to be quite adequate in shape. HERMES data do not need any
normalisation correction, while fits of the COMPASS data much improve with a
-dependent overall normalisation factor. A comparison of the extracted TMDs
with previous EMC and JLab data confirms the adequacy of the simple Gaussian
distributions. The possible role of the TMD evolution is briefly considered.Comment: 21 pages, 16 figure
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