Francesco Murgia

Single spin asymmetries in p↑p and inclusive processes

Abstract We consider several single spin asymmetries in inclusive p↑p and p ↑ p processes as higher twist QCD contributions, taking into account spin and intrinsic k ⊥ effects in the quark distribution functions. This approach has been previously applied to the description of the single spin asymmetries observed in p ↑ p→π X reactions and all its parameters fixed: we give here predictions for new processes, which agree with experiments for which data are available, and suggest further possible measurements.We consider several single spin asymmetries in inclusive, transversely polarized proton(antiproton) - proton processes as higher twist QCD contributions, taking into account spin and intrinsic transverse momentum effects in the quark distribution functions. This approach has been previously applied to the description of the single spin asymmetries observed in transversely polarized proton - proton -> pion + X reactions and all its parameters fixed: we give here predictions for new processes, which agree with experiments for which data are available, and suggest further possible measurements.

Parton intrinsic motion in inclusive particle production: Unpolarized cross sections, single spin asymmetries and the Sivers effect

The relevance of intrinsic (or primordial) transverse momentum of partons in the inclusive production of particles at high energy and moderately large

Spin effects in the fragmentation of a transversely polarized quark

{p}_{T}

Constraints on the gluon Sivers distribution via transverse single spin asymmetries at mid-rapidity in p(up) p ---> pi0 X processes at RHIC

has been known for a long time, beginning with Drell-Yan and diphoton processes, and continuing with photon and meson production in hadronic collisions. In view of its renewed interest in the context of polarized processes and single spin asymmetries we perform, in the framework of perturbative QCD with the inclusion of spin and

Importance of Lorentz structure in the parton model: Target mass corrections, transverse momentum dependence, positivity bounds

{\mathbit{k}}_{\ensuremath{\perp}}

Testing the process dependence of the Sivers function via hadron distributions inside a jet

effects, a detailed analysis of several such processes in different kinematical situations. We show that the inclusion of these effects leads, at the level of accuracy reachable in this approach, to an overall satisfactory agreement between theoretical predictions and experimental unpolarized data, thus giving support to the study of spin effects and single spin asymmetries within the same scheme. We present results for transverse single spin asymmetries, generated by the so-called Sivers effect, in inclusive pion and photon production in proton-proton collisions. We compare our results with the available experimental data and with previous results obtained using simplified versions of this approach.

Azimuthal asymmetries for hadron distributions inside a jet in hadronic collisions

Abstract An azimuthal dependence of pions produced in polarized Deep Inelastic Scattering, γ ∗ p ↑ →πX , has been recently observed and might be related to the so-called Collins effect. We discuss in details, for a general spin configuration of the nucleon, the kinematics of the process and methods of extracting information on the fragmentation properties of a polarized quark. Assuming that the observed azimuthal dependence is indeed due to Collins effect, we derive a lower bound estimate for the size of the quark analysing power, which turns out to be large.

The Sivers effect and the Single Spin Asymmetry A_N in p(transv. pol.) p --> h X processes

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.

Single spin asymmetries in inclusive hadron production from semiinclusive DIS to hadronic collisions: Universality and phenomenology

We show that respecting the underlying Lorentz structure in the parton model has very strong consequences. Failure to insist on the correct Lorentz covariance is responsible for the existence of contradictory results in the literature for the polarized structure function g{sub 2}(x), whereas with the correct imposition we are able to derive the Wandzura-Wilczek relation for g{sub 2}(x) and the target-mass corrections for polarized deep inelastic scattering without recourse to the operator product expansion. We comment briefly on the problem of threshold behavior in the presence of target-mass corrections. Careful attention to the Lorentz structure has also profound implications for the structure of the transverse momentum dependent parton densities often used in parton model treatments of hadron production, allowing the k{sub T} dependence to be derived explicitly. It also leads to stronger positivity and Soffer-type bounds than usually utilized for the collinear densities.

Transverse Lambda polarization in semi-inclusive DIS

Abstract We study the process dependence of the Sivers function by considering the impact of color-gauge invariant initial and final state interactions on transverse spin asymmetries in proton–proton scattering reactions within the framework of the transverse momentum dependent (TMD), generalized parton model. To this aim, we consider the azimuthal distribution of leading pions inside a fragmenting jet as well as single inclusive jet asymmetry in polarized proton–proton collisions. In contrast to single inclusive pion production, in both cases we can isolate the Sivers contribution and thereby study its process dependence. The predictions for the Sivers asymmetry obtained with and without inclusion of color gauge factors are comparable in size but with opposite signs. We conclude that both processes represent unique opportunities to discriminate among the two approaches and test the universality properties of the Sivers function in hadronic scattering reactions.