1,560 research outputs found
Double transverse-spin asymmetries in Drell--Yan and production from proton--antiproton collisions
We perform a NLO numerical study of the double transverse-spin asymmetries in
the resonance region for proton--antiproton collisions. We analyze the
large kinematic region, relevant for the proposed PAX experiment at GSI,
and discuss the implication of the results for the extraction of the
transversity densities.Comment: 8 pages, 6 figures, Talk given at "Transversity 2005" Como, Italy
7-10 Sep. 2005; eds. World Scientific in pres
Non-Universality and Evolution of the Sivers Function
We examine the large-x QCD evolution of the twist-three gluonic-pole strength
defining an effective T-odd Sivers function, where evolution of the T-even
transverse-spin DIS structure function g2 is multiplicative. The result
corresponds to a colour-factor modified spin-averaged twist-two evolution.Comment: Presented at the ECT* Workshop on Recent Advances in Perturbative QCD
and Hadronic Physics (20-25 July 2009} - final version (minor modifications
Single-Spin Asymmetries for Small-Angle Pion Production in High-Energy Hadron Collisions
Within the framework of a simple model, we study single-spin asymmetries for
pion production in hadron-hadron collisions at high-energies with one hadron
polarised. The asymmetries are generated via a mechanism of final (initial)
state interactions. For peripheral kinematics, when the pion belongs to the
fragmentation region of the polarised proton, we find non-zero asymmetries in
the high-energy limit. Numerical results and comparision with existing
experimental data are presented. We also discuss the relationship with odderon
exchange phenomenology.Comment: LaTeX2e, 12 pages, 4 figure files (2 TeX and 2 eps), uses axodraw,
and cite packages; submitted to Eur. Phys. J
Investigating Delamination Migration in Composite Tape Laminates
A modification to a recently developed test specimen designed to investigate migration of a delamination between neighboring ply interfaces in tape laminates is presented. The specimen is a cross-ply laminated beam consisting of 40 plies with a polytetrafluoroethylene insert spanning part way along its length. The insert is located between a lower 0-degree ply (specimen length direction) and a stack of four 90-degree plies (specimen width direction). The modification involved a stacking sequence that promotes stable delamination growth prior to migration, and included a relocation of the insert from the specimen midplane to the interface between plies 14 and 15. Specimens were clamped at both ends onto a rigid baseplate and loaded on their upper surface via a piano hinge assembly, resulting in a predominantly flexural loading condition. Tests were conducted with the load-application point positioned at various locations along a specimen's span. This position affected the sequence of damage events during a test
Ionospheric Power-Spectrum Tomography in Radio Interferometry
A tomographic method is described to quantify the three-dimensional
power-spectrum of the ionospheric electron-density fluctuations based on
radio-interferometric observations by a two-dimensional planar array. The
method is valid to first-order Born approximation and might be applicable to
correct observed visibilities for phase variations due to the imprint of the
full three-dimensional ionosphere. It is shown that not the ionospheric
electron density distribution is the primary structure to model in
interferometry, but its autocorrelation function or equivalent its
power-spectrum. An exact mathematical expression is derived that provides the
three dimensional power-spectrum of the ionospheric electron-density
fluctuations directly from a rescaled scattered intensity field and an incident
intensity field convolved with a complex unit phasor that depends on the w-term
and is defined on the full sky pupil plane. In the limit of a small field of
view, the method reduces to the single phase screen approximation. Tomographic
self-calibration can become important in high-dynamic range observations at low
radio frequencies with wide-field antenna interferometers, because a
three-dimensional ionosphere causes a spatially varying convolution of the sky,
whereas a single phase screen results in a spatially invariant convolution. A
thick ionosphere can therefore not be approximated by a single phase screen
without introducing errors in the calibration process. By applying a Radon
projection and the Fourier projection-slice theorem, it is shown that the
phase-screen approach in three dimensions is identical to the tomographic
method. Finally we suggest that residual speckle can cause a diffuse intensity
halo around sources, due to uncorrectable ionospheric phase fluctuations in the
short integrations, which could pose a fundamental limit on the dynamic range
in long-integration images.Comment: 8 pages; Accepted for publication in Ap
NNLO Corrections to the Polarized Drell-Yan Coefficient Function
We present the full next-to-next-to-leading order (NNLO) corrections to the
coefficient function for the polarized cross section of
the Drell-Yan process. We study the effect of these corrections on the process
at an C.M. energy . All QCD partonic
subprocesses have been included provided the lepton pair is created by a
virtual photon, which is a valid approximation for a lepton pair invariant mass
. For this reaction the dominant subprocess is given by and its higher order corrections so that it provides us with an
excellent tool to measure the polarized sea-quark densities.Comment: 5 pages, 5 figures, 7th DESY Workshop on Elementary Particle Theory,
Loops and Legs in Quantum Field Theory, Zinnowitz, Germany, April 25-30, 200
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