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      Soft-fermion-pole contribution to single-spin asymmetry for pion production in pp collisions

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          Abstract

          We study the single transverse spin asymmetry for the inclusive pion production in the nucleon-nucleon collision, p^\uparrow p\to\pi X, based on the twist-3 mechanism in the collinear factorization. We derive the soft-fermion-pole (SFP) contribution to the twist-3 single-spin-dependent cross section associated with the twist-3 quark-gluon correlation functions in the polarized nucleon. We find that the SFP can give rise to a large effect to the asymmetry A_N owing to the large partonic hard cross sections with the large color factor, if the SFP function has a similar magnitude as the soft-gluon-pole (SGP) function, in spite of the absence of the "derivative term" for the SFP function unlike for the SGP function.

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          Transverse Quark Polarization in Large-pTReactions,e+e−Jets, and Leptoproduction: A Test of Quantum Chromodynamics

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            Universality of soft and collinear factors in hard-scattering factorization

            Universality in QCD factorization of parton densities, fragmentation functions, and soft factors is endangered by the process dependence of the directions of Wilson lines in their definitions. We find a choice of directions that is consistent with factorization and that gives universality between e^+e^- annihilation, semi-inclusive deep-inelastic scattering, and the Drell-Yan process. Universality is only modified by a time-reversal transformation of the soft function and parton densities between Drell-Yan and the other processes, whose only effect is the known reversal of sign for T-odd parton densities like the Sivers function. The modifications of the definitions needed to remove rapidity divergences with light-like Wilson lines do not affect the results.
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              A Unified Picture for Single Transverse-Spin Asymmetries in Hard Processes

              Using Drell-Yan pair production as an example, we explore the relation between two well-known mechanisms for single transverse-spin asymmetries in hard processes: twist-three quark-gluon correlations when the pair's transverse momentum is large, \(q_\perp \gg \Lambda_{\rm QCD}\), and time-reversal-odd and transverse-momentum-dependent parton distributions when \(q_\perp\) is much less than the pair's mass. We find that although the two mechanisms have their own domain of validity, they describe the same physics in the kinematic region where they overlap. This unifies the two mechanisms and imposes an important constraint on phenomenological studies of single spin asymmetries.
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                Author and article information

                Journal
                11 March 2009
                2009-04-07
                Article
                10.1016/j.physletb.2009.04.017
                0903.1923
                90fc7cbf-febf-45b5-a2a7-60ff9e42b8b0

                http://arxiv.org/licenses/nonexclusive-distrib/1.0/

                History
                Custom metadata
                Phys.Lett.B675:181-189,2009
                16 pages, 9 figures, some references added, slight modification in discussions
                hep-ph

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