1,454 research outputs found
Photoproduction Processes in Polarized ep - Collisions at HERA
We study various conceivable photoproduction reactions in a polarized ep
collider mode of HERA with respect to their sensitivity to the proton's
polarized gluon distribution. A special emphasis is put on the `resolved' part
of the cross sections which in principle opens the possibility to determine for
the first time also the completely unknown parton content of longitudinally
polarized photons. In the very promising case of dijet production we also
investigate the impact of parton showering, hadronization and jet finding on
the parton level results.Comment: 16 pages, LaTeX, 7 figures, uses epsfig, amssymb, and a41 (included)
styles; Contribution to the proceedings of the 1997 workshop on 'Physics with
Polarized Protons at HERA', Hamburg and Zeuthen, Germany, March-September
199
Comment on soft-pion emission in DVCS
The soft-pion theorem for pion production in deeply virtual Compton
scattering, derived by Guichon, Mosse and Vanderhaegen, is shown to be
consistent with chiral perturbation theory. Chiral symmetry requires that the
nonsinglet operators corresponding to spin-independent and spin-dependent
parton distributions have the same anomalous dimensions in cases where those
operators are related by chiral transformations. In chiral perturbation theory,
their scale-dependences can thus be absorbed in the coefficents of the
corresponding effective operators, without affecting their chiral structures.Comment: 2 pages, RevTe
Helicity Parton Distributions at a Future Electron-Ion Collider: A Quantitative Appraisal
We present a quantitative assessment of the impact a future electron-ion
collider will have on determinations of helicity quark and gluon densities and
their contributions to the proton spin. Our results are obtained by performing
a series of global QCD analyses at next-to-leading order accuracy based on
realistic sets of pseudo-data for the inclusive and semi-inclusive
deep-inelastic scattering of longitudinally polarized electrons and protons at
different, conceivable center-of-mass system energies.Comment: 11 pages, 8 figure
Intrinsic parton motion soft mechanisms and the longitudinal spin asymmetry A_LL in high energy pp -> pi X
The longitudinal double spin asymmetry A_LL in the reaction pp --> pi X has
been measured at RHIC with extremely interesting consequences. If the gluon
polarization in a proton were as big as needed to resolve the famous "spin
crisis" then A_LL would be large and positive. Latest RHIC results indicate
that A_LL is small and disfavour large positive values of the gluon
polarization. We examine whether the soft mechanisms (Collins, Sivers,
Boer-Mulders), essential for generating transverse single spin asymmetries,
have any significant influence on A_LL, and whether they could alter the
conclusion that the gluon polarization is necessarily small. It turns out that
the contribution from these effects is essentially negligible.Comment: RevTeX, 9 pages, 3 eps figures. Revised and shortened version; title
slightly modified; figs. 3,4 removed; a new figure for the unpol. cross
section added; no changes in results and conclusions; matches the published
versio
A_{LT} in the Nucleon-Nucleon Polarized Drell-Yan Process
We present a leading order (LO) estimate for the longitidinal-transverse spin
asymmetry (A_{LT}) in the nucleon-nucleon polarized Drell-Yan process at RHIC
and HERA- energies in comparison with A_{LL} and A_{TT}. A_{LT}
receives contribution from g_1, the transversity ditribution h_1, and the
twist-3 distributions g_T and h_L. For the twist-3 contribution we use the bag
model prediction evolved to a high energy scale by the large-N_c evolution
equation. We found that A_{LT} (normalized by the asymmetry in the parton
level) is much smaller than the corresponding A_{TT}. Twist-3 contribution
given by the bag model also turned out to be negligible.Comment: Talk presented at the KEK-Tanashi International Conference "Physics
of Hadrons and Nuclei", Dec. 14-17, 1998, Tokyo. 4 pages in Latex. 1 figure
included as eps files using epsbox.st
Single-Inclusive Jet Production in Polarized pp Collisions at O(alpha_s^3)
We present a next-to-leading order QCD calculation for single-inclusive
high-p_T jet production in longitudinally polarized pp collisions within the
``small-cone'' approximation. The fully analytical expressions obtained for the
underlying partonic hard-scattering cross sections greatly facilitate the
analysis of upcoming BNL-RHIC data on the double-spin asymmetry A_{LL}^{jet}
for this process in terms of the unknown polarization of gluons in the nucleon.
We simultaneously rederive the corresponding QCD corrections to unpolarized
scattering and confirm the results existing in the literature. We also
numerically compare to results obtained with Monte-Carlo methods and assess the
range of validity of the ``small-cone'' approximation for the kinematics
relevant at BNL-RHIC.Comment: 23 pages, 8 eps-figure
Next-to-leading order QCD evolution of transversity fragmentation functions
We derive the next-to-leading order splitting kernels for the scale evolution
of fragmentation functions for transversely polarized quarks into transversely
polarized hadrons.Comment: 9 pages, LaTe
The corrosion of chromium based coatings for packaging steel
Chromium/chromium oxide based coatings, cathodically electrodeposited from either Cr (VI) or Cr (III) containing electrolytes are compared with respect to their ability to resist the corrosion driven delamination of an adherent polymer overcoat. Cathodic disbondment rates are determined using an in-situ scanning Kelvin probe technique. Anodic disbondment (filiform corrosion, FFC) rates are determined optically. The Cr (VI) derived coatings were fully resistant to corrosion driven disbondment. The Cr (III) derived coatings exhibited measurable rates of both FFC and cathodic disbondment. Disbondment kinetics are explained in relation to coating morphology, porosity and chemical composition determined using a combination of scanning electron microscopy (SEM), transmission electron microscopy (TEM) and xray photoelectron spectroscopy (XPS)
Drell-Yan forward-backward and spin asymmetries for arbitrary vector boson production at next-to-leading order
Longitudinally polarized, unpolarized and forward-backward mass differential
cross sections for Drell-Yan lepton-pair production by arbitrary vector bosons
are calculated in next-to-leading order (NLO) QCD. Analytical results are
presented in a form valid for all consistent -dimensional regularization
schemes, with the mass factorization scheme kept general. NLO predictions for
all Drell-Yan type processes (, and ) at BNL's
relativistic heavy ion collider (RHIC) are made using polarized parton
distributions which fit the recent deep-inelastic scattering data. These are
examined as tools in the determination of the polarized parton distributions
and the unpolarized ratio. NLO predictions for the
forward-backward lepton asymmetry at Fermilab are made and the precision
determination of from future runs is studied. In all the
above, the QCD corrections are found to be significant. An introductory
discussion is given of various theoretical issues, such as allowable
factorization and regularization schemes, and scale dependences.Comment: 34 pages, figures included, revtex. Some discussions and references
added/modified. In more compact form. To appear in Phys. Rev.
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