131 research outputs found

    Azimuthal asymmetries for hadron distributions inside jets in hadronic collisions

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    Using a generalized parton model approach including spin and intrinsic parton motion effects, and assuming the validity of factorization for large p_T jet production in hadronic collisions, we study the azimuthal distribution around the jet axis of leading pions, produced in the jet fragmentation process. We identify the observable leading-twist azimuthal asymmetries for the unpolarized and single-polarized case related to both quark and gluon-originated jets. We account for all physically allowed combinations of the transverse momentum dependent (TMD) parton distribution and fragmentation functions, with special attention to the Sivers, Boer-Mulders, and transversity quark distributions, and to the Collins fragmentation function for quarks (and to the analogous functions for gluon partons).Comment: 8 pages, 5 figures, to appear in the proceedings of 19th International Spin Physics Symposium (SPIN2010), Sep 27-Oct 2, 2010, Juelich (Germany

    Hadron Spin Structure: Novel Effects from Transverse Single Spin Asymmetries

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    Transverse single spin asymmetries can be a challenging tool in our understanding of the internal structure of hadrons. Some aspects and recent results are discussed.Comment: LaTeX 2e, 3 pages, 2 ps figures, uses aipproc.cls. Talk delivered at the 6th Conference on ``Quark Confinement and the Hadron Spectrum'', September 21-25, 2004, Villasimius, Ital

    Single spin asymmetries, unpolarized cross sections and the role of partonic transverse momentum

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    Partonic intrinsic transverse momentum can be essential for the explanation of large single spin asymmetries in hadronic reactions in the framework of perturbative QCD. The status of an ongoing program investigating in a consistent way the role of intrinsic transverse momentum both in unpolarized and polarized processes is discussed. We compute inclusive cross sections for hadron and photon production in hadronic collisions and for Drell-Yan processes; the results are compared with available experimental data in several different kinematical situations.Comment: LaTeX, 6 pages, 4 ps figures, uses graphicx.sty. Talk delivered by U. D'Alesio at the ``15th International Spin Physics Symposium'', SPIN2002, September 9-14, 2002, Brookhaven National Laboratory, Upton (NY), US

    Phenomenology of single transverse spin asymmetries

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    A unified and consistent phenomenological approach to single transverse spin asymmetries in the framework of perturbative QCD, with the inclusion of a new class of spin and k_T dependent distribution and fragmentation functions, is presented. As an example, results on A_N(p(pol) p --> pion X) and P_Lambda(p p -->Lambda(pol) X) are shown.Comment: 8 pages, 3 figures, uses epsfig.sty. Talk delivered by U. D'Alesio at the ``VIII Convegno su Problemi di Fisica Nucleare Teorica'', October 18-20, 2000, Cortona, Ital

    Transverse Momentum Dependent Distributions in Hadronic Collisions: p(transv. polarized) p --> D + X and p(transv. polarized) p --> gamma + X

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    Our understanding of the transverse spin structure of hadrons might definitely get improved by the information we gather on transverse momentum dependent (TMD) distributions. These new functions could also be crucial for a description of the observed transverse single spin asymmetries (SSA). In a hard scattering model for inclusive hadronic reactions, based on a generalized QCD factorization scheme, many mechanisms - namely the Sivers, Collins, Boer-Mulders effects - might contribute to a SSA. We show how the k_T dependent phases arising from the partonic kinematics together with a suitable choice of experimental configurations could help in disentangling the above mentioned effects. We discuss their potential role in two inclusive hadronic processes: heavy meson and photon production in pp and p pbar collisions.Comment: LaTeX 2e, 4 pages, 4 ps figures, uses aipproc.cls. Talk delivered by U. D'Alesio at the "17th International Spin Physics Symposium", SPIN2006, October 2-7, 2006, Kyoto, Japa

    Parton intrinsic motion: unpolarized cross sections and the Sivers effect in inclusive particle production

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    We present a detailed study, performed in the framework of LO perturbative QCD with the inclusion of spin and k_T effects, of unpolarized cross sections for the Drell-Yan process and for inclusive pion and photon production in hadronic collisions, in different kinematical situations. We find a satisfactory agreement between theoretical predictions and experimental data. This supports the study of spin effects and transverse single spin asymmetries (SSA) within the same scheme. We then present results for SSA, generated by the so-called Sivers effect, in inclusive pion production in proton-proton collisions.Comment: LaTeX2e, 4 pages, 4 ps figures, uses ws-procs9x6. Talk delivered by F. Murgia at the ``16th International Spin Physics Symposium'', SPIN2004, October 10-16, 2004, Trieste, Ital

    Transverse single-spin asymmetries in proton-proton collisions at the AFTER@LHC experiment in a TMD factorisation scheme

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    The inclusive large-pTp_T production of a single pion, jet or direct photon, and Drell-Yan processes, are considered for proton-proton collisions in the kinematical range expected for the fixed-target experiment AFTER, proposed at LHC. For all these processes, predictions are given for the transverse single-spin asymmetry, ANA_N, computed according to a Generalised Parton Model previously discussed in the literature and based on TMD factorisation. Comparisons with the results of a collinear twist-3 approach, recently presented, are made and discussed.Comment: RevTex4, 12 pages, 36 eps figures. V2: Few paragraphs and comments added. Several references added. Results unchanged. Matches the published versio
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