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      Handedness of direct photons

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          Abstract

          The azimuthal asymmetry of direct photons originating from primary hard scatterings between partons is calculated. This can be accounted for by the inclusion of the color dipole orientation, which is sensitive to the rapid variation of the nuclear profile. To this end we introduce the dipole orientation within the saturation model of Golec-Biernat and W\"usthoff, while preserving all its features at the cross-section level. We show that the direct photon elliptic anisotropy v2 coming from this mechanism changes sign and becomes negative for peripheral collisions, albeit it is quite small for nuclear collisions at the RHIC energy.

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          Most cited references15

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          Nuclear charge-density-distribution parameters from elastic electron scattering

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            Photo-induced charge transfer across the interface between organic molecular crystals and polymers

            Photo-induced charge transfer of positive and negative charges across the interface between an ordered organic semiconductor and a polymeric insulator is observed in the field-effect experiments. Immobilization of the transferred charge in the polymer results in a shift of the field-effect threshold of polaronic conduction along the interface in the semiconductor, which allows for direct measurements of the charge transfer rate. The transfer occurs when the photon energy exceeds the absorption edge of the semiconductor. The direction of the transverse electric field at the interface determines the sign of the transferred charge; the transfer rate is controlled by the field magnitude and light intensity.
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              Bremsstrahlung of a Quark Propagating through a Nucleus

              The density of gluons produced in the central rapidity region of a heavy ion collision is poorly known. We investigate the influence of the effects of quantum coherence on the transverse momentum distribution of photons and gluons radiated by a quark propagating through nuclear matter. We describe the case that the radiation time substantially exceeds the nuclear radius (the relevant case for RHIC and LHC energies), which is different from what is known as Landau-Pomeranchuk-Migdal effect corresponding to an infinite medium. We find suppression of the radiation spectrum at small transverse photon/gluon momentum k_T, but enhancement for k_T>1GeV. Any nuclear effects vanish for k_T > 10GeV. Our results allow also to calculate the k_T dependent nuclear effects in prompt photon, light and heavy (Drell-Yan) dilepton and hadron production.
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                Author and article information

                Journal
                14 April 2008
                Article
                10.1590/S0103-97332008000400012
                0804.2283
                49559e42-110c-4917-a6e2-fdf991139d3e

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

                History
                Custom metadata
                USM-TH-228
                Braz.J.Phys.38:443-448,2008
                6 pages, 6 figures, Based on talk given by A.H.R. at II LAWHEP, Sao Miguel das Missoes, Brazil, December 3-7, 2007
                hep-ph

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