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

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

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

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

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

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

Cross sections and single spin asymmetries in hadronic collisions with intrinsic transverse momentum effects

The role of intrinsic transverse momentum both in unpolarized and polarized processes is discussed. We consider inclusive cross sections for pion production in hadronic collisions and for Drell-Yan processes; the results are compared with available experimental data in several different kinematical situations. We reanalyze transverse single spin asymmetries (SSA) observed in inclusive pion production, p(transv. polarized) p --> pion + X, in terms of Sivers effect and show how it can be disentangled in polarized Drell-Yan processes by suitably integrating over some final configurations. Estimates for RHIC experiments are given.Comment: LaTeX, 8 pages, 4 ps figures, uses epsfig.sty. Talk delivered by F. Murgia at the "IX Convegno su Problemi di Fisica Nucleare Teorica", October 9-12, 2002, Cortona, Ital

A general formalism for single and double spin asymmetries in inclusive hadron production

We present a calculation of single and double spin asymmetries for inclusive hadron production in hadronic collisions. Our approach is based on Leading Order (LO) perturbative QCD and generalized factorization theorems, with full account of intrinsic parton momentum, k_T, effects. This leads to a new class of spin and k_T-dependent distribution and fragmentation functions. Limiting ourselves to consider leading twist functions, we show how they could play a relevant role in producing non-vanishing spin asymmetries.Comment: LaTeX, 8 pages, uses ws-procs9x6.cls. Talk delivered by S. Melis at the ``X Convegno su Problemi di Fisica Nucleare Teorica'', October 6-9, 2004, Cortona, Ital