Single spin asymmetries in inclusive hadron production from SIDIS to hadronic collisions: universality and phenomenology

In a perturbative QCD approach, with inclusion of spin and transverse momentum effects, experimental data on azimuthal asymmetries observed in polarized semi-inclusive deeply inelastic scattering and e+ e- annihilations can be used to determine the Sivers, transversity and Collins soft functions. By using these functions, within the same scheme, we predict p(transv. polarized) p -> h + X single spin asymmetries in remarkable agreement with RHIC experimental data.Comment: 5 pages, 6 ps figure

Exploring the transverse spin structure of the nucleon

We discuss our present understanding of the transverse spin structure of the nucleon and of related properties originating from parton transverse motion. Starting from the transversity distribution and the ways to access it, we then address the role played by spin and transverse momentum dependent (TMD) distributions in azimuthal and transverse single spin asymmetries. The latest extractions of the Sivers, Collins and transversity functions are also presented.Comment: 8 pages, 6 ps figures, uses aipproc.cls. Invited talk at "6th International Conference on Perspectives in Hadronic Physics (Hadron 08)", Trieste, Italy, 12-18 May 2008. Submitted to AIP Conf.Pro

General partonic structure for hadronic spin asymmetries

The high energy and large p_T inclusive polarized process, (A, S_A) + (B, S_B) --> C + X, is considered under the assumption of a generalized QCD factorization scheme. For the first time all transverse motions, of partons in hadrons and of hadrons in fragmenting partons, are explicitly taken into account; the elementary interactions are computed at leading order with noncollinear exact kinematics, which introduces many phases in the expressions of their helicity amplitudes. Several new spin and k_T dependent soft functions appear and contribute to the cross sections and to spin asymmetries; we put emphasis on their partonic interpretation, in terms of quark and gluon polarizations inside polarized hadrons. Connections with other notations and further information are given in some Appendices. The formal expressions for single and double spin asymmetries are derived. The transverse single spin asymmetry A_N, for p(transv. polarized) p --> pion + X processes is considered in more detail, and all contributions are evaluated numerically by saturating unknown functions with their upper positivity bounds. It is shown that the integration of the phases arising from the noncollinear kinematics strongly suppresses most contributions to the single spin asymmetry, leaving at work predominantly the Sivers effect and, to a lesser extent, the Collins mechanism.Comment: RevTeX, 46 pages, 5 ps figures. v2: some clarifying comments and appendix on kinematics added, references updated, published versio

General helicity formalism for two-hadron production in e+e− annihilation within a TMD approach

We present the complete leading-order results for the azimuthal dependences and polarization observables in e+ e− - > h1 h2 + X processes, where the two hadrons are produced almost back-to-back, within a transverse momentum dependent (TMD) factorization scheme. We consider spinless (or unpolarized) and spin-1/2 hadron production and give the full set of the corresponding quark and gluon TMD fragmentation functions (TMD-FFs). By adopting the helicity formalism, which allows for a more direct probabilistic interpretation, single- and double-polarization cases are discussed in detail. Simplified expressions, useful for phenomenological analyses, are obtained by assuming a factorized Gaussian-like dependence on intrinsic transverse momenta for the TMD-FFs

Transverse Λ polarization in e+e− annihilations and in SIDIS processes at the EIC within TMD factorization

We present a phenomenological study on the role of charm contribution and SU(2) isospin symmetry in the extraction of the Λ polarizing fragmentation functions from e+e−→Λ↑(Λbar↑)h+X annihilation processes. We adopt the well-established transverse-momentum-dependent factorization formalism, within the Collins-Soper-Sterman evolution scheme at next-to-leading logarithm accuracy, carefully exploiting the role of the nonperturbative component of the polarizing fragmentation function. We then discuss the impact of these results on the predictions for transverse Λ, Λbar polarization in semi-inclusive deep inelastic scattering processes at typical energies of the future Electron-Ion Collider

The role of Cahn and Sivers effects in Deep Inelastic Scattering

The role of intrinsic \bfk_\perp in inclusive and semi-inclusive Deep Inelastic Scattering processes ($\ell p \to \ell h X$) is studied with exact kinematics within QCD parton model at leading order; the dependence of the unpolarized cross section on the azimuthal angle between the leptonic and the hadron production planes (Cahn effect) is compared with data and used to estimate the average values of $k_\perp$ both in quark distribution and fragmentation functions. The resulting picture is applied to the description of the weighted single spin asymmetry $A_{UT}^{\sin(\phi_\pi - \phi_S)}$ recently measured by the HERMES collaboration at DESY; this allows to extract some simple models for the quark Sivers functions. These are compared with the Sivers functions which succeed in describing the data on transverse single spin asymmetries in \pup p \to \pi X processes; the two sets of functions are not inconsistent. The extracted Sivers functions give predictions for the COMPASS measurement of $A_{UT}^{\sin(\phi_\pi - \phi_S)}$ in agreement with recent preliminary data, while their contribution to HERMES $A_{UL}^{\sin\phi_\pi}$ is computed and found to be small. Predictions for $A_{UT}^{\sin(\phi_K - \phi_S)}$ for kaon production at HERMES are also given.Comment: 21 pages, 12 figures, revtex, version published in PRD, one figure, comments and references adde

Constraints on the gluon Sivers distribution via transverse single spin asymmetries at midrapidity in p(transv. polarized) p -> pi^0 X processes at BNL RHIC

We consider the recent RHIC data on the transverse single spin asymmetry (SSA) A_N, measured in p(transv. polarized) p -> pi^0 X processes at mid-rapidity by the PHENIX collaboration. The measurement is consistent with a vanishing SSA. We analyze this experimental information within a hard scattering approach based on a generalized QCD factorization scheme, with unintegrated, transverse momentum dependent (TMD), parton distribution and fragmentation functions. It turns out that, in the kinematical region of the data, only the gluon Sivers effect could give a large contribution to A_N; its vanishing value is thus an indication about the possible size of the gluon Sivers function (GSF). Approximate upper limits on its magnitude are derived. Additional constraints obtained combining available parameterizations of the quark Sivers function and the Burkardt sum rule (BSR) for the Sivers distributions are also discussed.Comment: RevTeX, 8 pages, 2 ps figures; v2: few clarifying comments, a "note added in proof" and some references added; version published in Phys. Rev.

VERSO LO SVILUPPO DI UN SILLABO FRASEOLOGICO PER L’APPRENDIMENTO DELL’ITALIANO L2: ALCUNE PREMESSE TEORICO-METODOLOGICHE

Le combinazioni lessicali sono centrali nell’apprendimento linguistico perché possono essere elaborate velocemente (Siyanova-Chanturia, 2015) e il loro uso contribuisce a dare l’idea di fluenza in produzione (Nattinger & DeCarrico, 1992). Tuttavia, l'acquisizione della competenza fraseologica in L2 è fonte di difficoltà per gli apprendenti. Nei sillabi per l’insegnamento della lingua italiana, inoltre, il lessico è generalmente presentato sotto forma di elenco di singole parole e la dimensione fraseologica risulta assente. Sarebbe quindi utile sviluppare un sillabo che tenga conto di questa dimensione. Come afferma Luoni (2016), nel sillabo gli item linguistici devono essere organizzati considerando la complessità dei processi comunicativi e dei processi di apprendimento e di acquisizione. Il sillabo fraseologico dovrebbe, pertanto, integrare funzioni comunicative e misure di complessità fraseologica. In questo contributo, presentiamo una riflessione teorico-metodologica che rappresenta la necessaria premessa per lo sviluppo di un sillabo fraseologico che tenga conto di misure di complessità fraseologica, definite tramite metodologie computazionali e psicolinguistiche, e di funzioni comunicative e argomenti caratteristici di ciascun livello di competenza. TOWARDS THE DEVELOPMENT OF A PHRASEOLOGICAL SYLLABUS FOR LEARNING ITALIAN L2: SOME THEORETICAL-METHODOLOGICAL PREMISES Lexical combinations are central to language learning because they can be processed quickly (Siyanova-Chanturia, 2015) and their use gives the idea of fluency in production (Nattinger & DeCarrico, 1992). However, the acquisition of L2 phraseological competence is difficult for learners. Furthermore in Italian L2 syllabuses, vocabulary is often presented as a list of words and the phraseological dimension is usually absent. To fill this gap, a phraseological syllabus should be designed. As stated by Luoni (2016), linguistic items in the syllabus should be organized taking into account the complexity of the communication processes and the complexity of the learning and acquisition processes. Thus, the phraseological syllabus should integrate communicative functions and measures of phraseological complexity. In this article, we discuss the theoretical and methodological premises for the development of a phraseological syllabus that takes into account measures of phraseological complexity that are defined through computational and psycholinguistic methodologies and the communicative functions and topics that characterize each proficiency level.

General Helicity Formalism for Polarized Semi-Inclusive Deep Inelastic Scattering

We study polarized Semi-Inclusive Deep Inelastic Scattering (SIDIS) processes, within the QCD parton model and a factorization scheme, taking into account all transverse motions, of partons inside the initial proton and of hadrons inside the fragmenting partons. We use the helicity formalism. The elementary interactions are computed at LO with non collinear exact kinematics, which introduces phases in the expressions of their helicity amplitudes. Several Transverse Momentum Dependent (TMD) distribution and fragmentation functions appear and contribute to the cross sections and to spin asymmetries. Our results agree with those obtained with different formalisms, showing the consistency of our approach. The full expression for single and double spin asymmetries is derived. Simplified, explicit analytical expressions, convenient for phenomenological studies, are obtained assuming a factorized Gaussian dependence on intrinsic momenta for the TMDs.Comment: 29 pages, 2 figure

Physics Opportunities of a Fixed-Target Experiment using the LHC Beams

We outline the many physics opportunities offered by a multi-purpose fixed-target experiment using the LHC proton and Pb beams extracted by a bent crystal. In a proton run with the LHC 7-TeV beam, one can analyze pp, pd and pA collisions at sqrt(s_NN)~115 GeV and even higher using the Fermi motion in a nuclear target. In a Pb run with a 2.76 TeV-per-nucleon beam, sqrt(s_NN) is as high as 72 GeV. Bent crystals can be used to extract about 5x10^8 protons/s; the integrated luminosity over a year reaches 0.5fb-1 on a typical 1 cm-long target without species limitation. Such an extraction mode does not alter the performance of the collider experiments at the LHC. By instrumenting the target-rapidity region, gluon and heavy-quark proton and neutron PDFs can be accessed at large x and even at x larger than 1 in the nuclear case. Single diffractive physics and, for the first time, the large negative-xF domain can be accessed. The nuclear target-species versatility provides a unique opportunity to study nuclear matter vs. the features of the hot and dense matter formed in heavy-ion collisions, which can be studied in PbA collisions over the full range of target-rapidity domain with a large variety of nuclei. The polarization of hydrogen and nuclear targets allows an ambitious spin program, including measurements of the QCD lensing effects which underlie the Sivers single-spin asymmetry, the study of transversity distributions and possibly of polarized PDFs. We also emphasize the potential offered by pA ultra-peripheral collisions where the nucleus target A is used as a coherent photon source, mimicking photoproduction processes in ep collisions. Finally, we note that W and Z bosons can be produced and detected in a fixed-target experiment and in their threshold domain for the first time, providing new ways to probe the partonic content of the proton and the nucleus.Comment: 14 pages, 2 figures, 5 tables. Comments are welcom