3,594 research outputs found
Probing the parton densities of polarized photons at a linear e^+e^- collider
The present theoretical status of spin-dependent parton densities Delta
f^{\gamma}(x,Q^2) of circularly polarized photons is briefly reviewed. It is
then demonstrated that measurements of the deep-inelastic spin asymmetry
A_1^{\gamma}\simeq g_1^{\gamma}/F_1^{\gamma} and of di-jet rapidity
distributions at a future linear e^+e^- collider appear to be particularly
suited for a determination the spin-dependent photonic quark and gluon
densities, respectively. Special emphasis is devoted to a comparison of the
different sources of polarized photons at a linear collider: the equivalent
photon approximation and backscattered laser (Compton) photons. It is shown
that backscattered laser photons are highly favorable, even indispensable, for
decent measurements of the Delta f^{\gamma}(x,Q^2).Comment: 7 pages, LaTeX, 4 eps figures, uses amssymb, espcrc2 (included), and
epsfig styles; Contribution to the Proceedings of the `International
Conference on the Structure and Interactions of the Photon (Photon99)' [Nucl.
Phys. B (Proc. Suppl.)], Freiburg, Germany, May 199
Next-to-Leading Order QCD Corrections to the Polarized Photoproduction of Heavy Flavors
We present a calculation of the next-to-leading order (O(alpha_s^2 alpha))
QCD corrections to heavy flavor photoproduction with longitudinally polarized
beams. We apply our results to study the longitudinal spin asymmetry for the
total charm quark production cross section which will be utilized by the
forthcoming COMPASS experiment at CERN to obtain first direct information on
the polarized gluon density Delta g. We also briefly discuss the main
theoretical uncertainties inherent in this calculation. In particular we
demonstrate that the factorization scale dependence is considerably reduced in
next-to-leading order.Comment: 18 pages, LaTeX, 4 figures, uses epsfig and amssymb style
Double-transverse spin asymmetries at NLO
We report on a next-to-leading order QCD calculation of the cross section and
the spin asymmetry for isolated large-p_T prompt photon production in
collisions of transversely polarized protons. Corresponding measurements may be
used at RHIC to determine the transversity parton distributions of the proton.Comment: 3 pages, LaTeX, 1 figure as eps file. Invited talk presented by W.
Vogelsang at the "Conference on the Intersections of Particle and Nuclear
Physics (CIPANP 2003)", New York City, May 19-24, 200
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