Azimuthal distributions of pions inside a jet in hadronic collisions

Using a generalized parton model approach including spin and intrinsic parton motion effects, and assuming the validity of factorization for large pT 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, which are generated by all the physically allowed combinations of transverse momentum dependent (TMD) parton distribution and fragmentation functions. In particular, we show how one can isolate the Collins and Sivers contributions, and suggest a test of the process dependence of the Sivers function by considering the effect of color-gauge invariant initial and final state interactions.Comment: 6 pages, 3 figures, to appear in the proceedings of Third International Workshop on Transverse Polarization Phenomena in Hard Scattering (Transversity 2011), Veli Lo\v{s}inj (Croatia), 29 August-2 September 201

Azimuthal distributions of pions inside jets at RHIC

We evaluate the azimuthal asymmetries for the distributions of leading pions inside a jet, produced in high-energy proton-proton collisions, in kinematic configurations currently under active investigation at RHIC. Adopting a transverse momentum dependent approach, which assumes the validity of a perturbative QCD factorization scheme and takes into account all the spin and intrinsic parton motion effects, we show how the main mechanisms underlying these asymmetries, namely the Sivers and the Collins effects, can be disentangled. Furthermore, we consider the impact of color-gauge invariant initial and final state interactions and suggest a method for testing the universality properties of the Sivers function for quarks.Comment: 4 pages, 3 figures, to appear in the proceedings of the 3rd Workshop on the QCD structure of the nucleon (QCD-N'12), Bilbao (Spain), 22-26 October 201

Testing the universality of the Collins function in pion-jet production at RHIC

By adopting a generalised parton model approach at leading order in QCD, including spin and intrinsic parton motion effects, we study the Collins azimuthal asymmetries for pions within a large-$p_T$ jet produced at mid-rapidity in polarised hadronic collisions. Using available information on the quark transversity distributions and the pion Collins functions, as extracted from semi-inclusive deeply inelastic scattering and $e^+e^-\to h_1 h_2\, X$ processes, we compute estimates for the Collins asymmetries in kinematical configurations presently investigated at RHIC by the STAR Collaboration. Collins-like asymmetries, involving linearly polarised gluons, are also considered. Our predictions, compared against available preliminary data, show a very good agreement, even if some discrepancies, to be further scrutinized both theoretically and experimentally, appear in the transverse momentum dependence of the Collins asymmetry. These results are in favour of the predicted universality of the Collins function and of a mild, if any, evolution with the hard scale of the asymmetries.Comment: 10 pages, 5 figures (10 plots); v2: discussion on jet kT dependence of the SSAs extended and one plot on the corresponding unpolarized cross section added (Fig. 3, right panel); few comments on factorization breaking effects and on the universality issue of the Collins function added; three references added; results unchanged; matches the published versio

Probing the gluon Sivers function in p↑p→J/ψ Xp^\uparrow p\to J/\psi\,X and p↑p→D Xp^\uparrow p \to D\,X

We present a study of transverse single-spin asymmetries (SSAs) in $p^\uparrow p\to J/\psi\,X$ and $p^\uparrow p\to D X$ within the framework of the generalized parton model (GPM), which includes both spin and transverse momentum effects, and show how they can provide useful information on the still almost unknown gluon Sivers function. Moreover, by adopting a modified version of this model, named color gauge invariant (CGI) GPM, we analyze the impact of the initial- and final-state interactions on our predictions. As a consequence, we find that these two processes are sensitive to different gluon Sivers functions, which can be expressed as linear combinations of two distinct, universal gluon distributions. We therefore define proper observables which could allow for a separate extraction of these two independent Sivers functions. At the same time, we show how it would be possible to discriminate between the GPM and the CGI-GPM approaches by comparing the corresponding estimates of SSAs with present and future experimental results at RHIC.Comment: 19 pages, 8 figures, 1 table; v2: minor changes, matches the published versio

Unraveling the Gluon Sivers Function in Hadronic Collisions at RHIC

We study the transverse single-spin asymmetries for $p^\uparrow p\to \pi\, X$ and $p^\uparrow p\to \gamma\, X$ within the so-called color gauge invariant generalized parton model (CGI-GPM) which, in addition to spin and transverse momentum effects, includes initial and final state interactions with the polarized proton remnants. We compute all relevant contributions, focusing in particular on the process dependence of the gluon Sivers function, which, for these processes, can always be expressed as a linear combination of two independent, universal terms. This study extends and completes a previous one, where only quark initiated partonic processes were considered. We then perform a combined phenomenological analysis of RHIC data on transverse single-spin asymmetries in $p^\uparrow p\to \pi\, X$ and $p^\uparrow p\to D\, X$, putting the first preliminary constraints on these two gluon Sivers functions. We show how their size can be estimated by means of these data, and use our results to provide predictions for the process $p^\uparrow p\to J/\psi\,X$, comparing them with data, and $p^\uparrow p\to \gamma\, X$, for which experimental information will soon become available. Corresponding estimates within the simpler GPM approach, without initial and final state interactions and with a single universal gluon Sivers function, are also given, showing that a clear discrimination between these two models is, for the moment, not possible.Comment: 17 pages, 9 figures (19 plots), 4 table

Azimuthal asymmetries for hadron distributions inside jets in hadronic collisions

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

La Fenomenologia dello spirito di Hegel: Problemi e interpretazioni

[English]:The volume collects essays dedicated to the Phenomenology of the spirit of G.W.F. Hegel and to some of its main interpretations. It gathers critical essays on the Hegelian masterpiece and studies on Hegel’s influences on authors such as Marx, Gentile, Heidegger, Kojève, Paci, Lacan and Brandom. These contributions investigate some categorical nodes that have marked ensuing ethical, theoretical, philosophical-political and later psychoanalytic reflections: dialectic, culture, negation, desire, body, phenomenon, recognition. Therefore, this collection does not intend to mark a specific interpretation of the Hegelian text. Rather, the authors share the effort to illustrate in actu exercito the possibilities given by these two extremes – the text and its interpretation – in which later philosophical culture has moved. Through this movement the Phenomenology of the spirit continues to produce Philosophy, intended as an opportunity and an instrument for the understanding of "one's own time with thought". In addition to the editors, the volume hosts contributions from: Stefania Achella, Rossella Bonito Oliva, Alessio Calabrese, Teresa Caporale, Alessandro De Cesaris, Giuseppe Antonio Di Marco, Gianluca Garelli, Roberto Morani, Anna Pia Ruoppo./ [Italiano]: Il volume raccoglie saggi dedicati alla Fenomenologia dello spirito di G.W.F. Hegel e ad alcune sue principali interpretazioni. A scritti dal taglio più nettamente storiografico che ne ricostruiscono le influenze in autori quali Marx, Gentile, Heidegger, Kojève, Paci, Lacan e Brandom, si affiancano contributi volti a ricostruire alcuni nodi categoriali che, sollecitati dal testo hegeliano, hanno segnato le riflessioni etiche, teoretiche, filosofico-politiche e psicoanalitiche successive: dialettica, cultura, negazione, desiderio, corpo, fenomeno, riconoscimento. Questa raccolta non intende quindi né riproporre la lettera del testo hegeliano, né avanzare una sua specifica interpretazione. Piuttosto, gli autori hanno condiviso lo sforzo di illustrare in actu exercito le possibilità di movimento tra questi due estremi – testo e interpretazione – tra cui la cultura filosofica si muove. Attraverso questo movimento la Fenomenologia dello spirito continua a produrre filosofia, ossia ad essere occasione e strumento per la comprensione del “proprio tempo col pensiero”

Collins and Sivers effects in p(transv. polarized) p --> jet pion X: Universality and process dependence

In this paper we briefly review the transverse momentum dependent generalized parton model and its application to the study of azimuthal asymmetries in the distribution of leading hadrons (mainly pions) inside large transverse momentum jets inclusively produced in polarized proton-proton collisions. We put particular emphasis on the phenomenological interest of these observables, in combination with similar asymmetries measured in semi-inclusive deeply inelastic scattering, Drell-Yan processes and e+e- collisions, for the study of the universality properties of the transverse momentum dependent parton distribution and fragmentation functions. We present results for RHIC kinematics at center-of-mass energies sqrt{s} = 200 and 500 GeV, for central and mainly forward jet rapidities, in particular for the Sivers distribution and the Collins fragmentation function, that are believed to be responsible of many of the largest asymmetries measured in the last years. We also briefly discuss the case of inclusive jet production and recent phenomenological applications of other theoretical approaches, like the colour gauge invariant generalized parton model and the collinear twist-three approach, aiming at clarifying the issues of the universality and process dependence of transverse momentum dependent functions.Comment: RevTeX, 16 pages, 9 figures with 19 eps files; Invited mini-review contribution to the Special Issue on "Path Dependence in Quantum Physics: From High-Order QCD to Wilson Lines and the Breakdown of Universality", to be published in Physics of Particles and Nucle

Azimuthal asymmetries in p↑p→jet π Xp^\uparrow p \to {\rm jet}\, \pi\, X

We study the azimuthal asymmetries for the distributions of leading pions inside a jet produced inclusively in high-energy proton-proton collisions within the framework of the transverse momentum dependent generalized parton model. We present results for the RHIC center-of-mass energies $\sqrt{s}$ = 200 and 500 GeV, mainly for forward jet rapidities, in particular for the two mechanisms which dominate such asymmetries: the Sivers and the Collins effects. We also briefly discuss the case of inclusive jet production and, adopting the so-called colour gauge invariant parton model, we propose a phenomenological analysis of the process dependence of the quark Sivers function.Comment: 6 pages, 6 figures, to appear in the Proceedings of the Fourth International Workshop on Transverse Polarisation Phenomena in Hard Processes (Transversity 2014), Chia, Cagliari (Italy), 9-13 June 201