23 research outputs found
Reviewing model calculations of the Collins fragmentation function
The Collins fragmentation function describes a left/right asymmetry in the
fragmentation of a transversely polarized quark into a hadron in a jet. Four
different model calculations of the Collins function have been presented in the
literature. While based on the same concepts, they lead to different results
and in particular to different signs for the Collins function. The purpose of
the present work is to review the features of these models and correct some
errors made in previous calculations. A full study of the parameter dependence
and the possible modifications to these models is beyond the scope of the
paper. However, some general conclusions are drawn
Unpolarized fragmentation function for the pion and kaon via the nonlocal chiral-quark model
In this talk we present our recent studies for the unpolarized fragmentation
functions for the pion and kaon, employing the nonlocal chiral quark model,
which manifests the nonlocal interaction between the quarks and pseudoscalar
mesons, in the light-cone frame. It turns out that the nonlocal interaction
produces considerable differences in comparison to typical local-interaction
models.Comment: 4 pages, 2 figures, Talk given at the international conference The
Fifth Asia-Pacific Conference on Few-Body Systems in Physics 2011 (APFB2011),
Seoul, Republic of Korea, 22-26 August 201
Momentum sum rules for fragmentation functions
Momentum sum rules for fragmentation functions are considered. In particular,
we give a general proof of the Sch\"afer-Teryaev sum rule for the transverse
momentum dependent Collins function. We also argue that corresponding sum rules
for related fragmentation functions do not exist. Our model-independent
analysis is supplemented by calculations in a simple field-theoretical model.Comment: 12 pages; v2: Eqs. (44,46) added, minor additional changes, to appear
in Phys. Lett.
Angular dependences in inclusive two-hadron production at BELLE
A collection of results is presented relevant for the analysis of azimuthal
asymmetries in inclusive two-hadron production at BELLE. The aim of this
overview is to provide theoretical ingredients necessary to extract the Collins
effect fragmentation function. The latter arises within the Collins-Soper
factorization formalism, which describes both the transverse momentum and Q^2
dependence of the cross section and its angular dependences at low and moderate
transverse momentum. Since the Collins effect is not the only source of angular
dependences, a discussion of various other effects is included. This concerns
higher twist contributions, photon-Z-boson interference effects, radiative
corrections, beam polarization and weak decays. Furthermore, different frames,
transverse momentum weighting and ratios of asymmetries are discussed. These
issues are all of relevance for the unambiguous measurement of the Collins
effect.Comment: 37 pages, 7 eps figures; mostly modifications in sections IX and XI,
minor changes also in sections III,VI,X
Azimuthal and Single Spin Asymmetries in Hard Scattering Processes
In this article we review the present understanding of azimuthal and single
spin asymmetries for inclusive and semi-inclusive particle production in
unpolarized and polarized hadronic collisions at high energy and moderately
large transverse momentum. After summarizing the experimental information
available, we discuss and compare the main theoretical approaches formulated in
the framework of perturbative QCD. We then present in some detail a
generalization of the parton model with inclusion of spin and intrinsic
transverse momentum effects. In this context, we extensively discuss the
phenomenology of azimuthal and single spin asymmetries for several processes in
different kinematical configurations. A comparison with the predictions of
other approaches, when available, is also given. We finally emphasize some
relevant open points and challenges for future theoretical and experimental
investigation.Comment: 70 pages, 34 ps figures. Invited review paper to be published in
Progress in Particle and Nuclear Physic
Transverse Spin Structure of the Nucleon through Target Single Spin Asymmetry in Semi-Inclusive Deep-Inelastic Reaction at Jefferson Lab
Jefferson Lab (JLab) 12 GeV energy upgrade provides a golden opportunity to
perform precision studies of the transverse spin and
transverse-momentum-dependent structure in the valence quark region for both
the proton and the neutron. In this paper, we focus our discussion on a
recently approved experiment on the neutron as an example of the precision
studies planned at JLab. The new experiment will perform precision measurements
of target Single Spin Asymmetries (SSA) from semi-inclusive electro-production
of charged pions from a 40-cm long transversely polarized He target in
Deep-Inelastic-Scattering kinematics using 11 and 8.8 GeV electron beams. This
new coincidence experiment in Hall A will employ a newly proposed solenoid
spectrometer (SoLID). The large acceptance spectrometer and the high polarized
luminosity will provide precise 4-D (, , and ) data on the
Collins, Sivers, and pretzelocity asymmetries for the neutron through the
azimuthal angular dependence. The full 2 azimuthal angular coverage in the
lab is essential in controlling the systematic uncertainties. The results from
this experiment, when combined with the proton Collins asymmetry measurement
and the Collins fragmentation function determined from the ee collision
data, will allow for a quark flavor separation in order to achieve a
determination of the tensor charge of the d quark to a 10% accuracy. The
extracted Sivers and pretzelocity asymmetries will provide important
information to understand the correlations between the quark orbital angular
momentum and the nucleon spin and between the quark spin and nucleon spin.Comment: 23 pages, 13 figures, minor corrections, matches published versio
Precise Measurements of Beam Spin Asymmetries in Semi-Inclusive production
We present studies of single-spin asymmetries for neutral pion
electroproduction in semi-inclusive deep-inelastic scattering of 5.776 GeV
polarized electrons from an unpolarized hydrogen target, using the CEBAF Large
Acceptance Spectrometer (CLAS) at the Thomas Jefferson National Accelerator
Facility. A substantial amplitude has been measured in the
distribution of the cross section asymmetry as a function of the azimuthal
angle of the produced neutral pion. The dependence of this amplitude
on Bjorken and on the pion transverse momentum is extracted with
significantly higher precision than previous data and is compared to model
calculations.Comment: to be submitted PL