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

The inclusive large-$p_T$ 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, $A_N$, 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

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

Constraints on Gluon Sivers Distribution from RHIC Results

We consider the recent RHIC data on the transverse single spin asymmetry (SSA) A_N, measured in p(transv. polarized) p --> pion X processes at mid-rapidity by the PHENIX Collaboration. 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. In this kinematical region, only the gluon Sivers effect could give a large contribution to A_N; its vanishing value is thus used to give approximate upper limits on the gluon Sivers function (GSF). Additional constraints from the Burkardt sum rule for the Sivers distributions are also discussed.Comment: LaTeX 2e, 4 pages, 2 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

Sivers and Collins effects in polarized pp scattering processes

We summarize the present phenomenology of Sivers and Collins effects for transverse single spin asymmetries in polarized proton-proton collisions within the framework of the generalized parton model (GPM). We will discuss a reassessment of the Collins effect and some preliminary predictions for SSA's in p(pol) p -> pi,K + X processes at RHIC obtained using updated information from SIDIS data and a new set of meson fragmentation functions.Comment: 8 pages, 10 eps figures, uses ws-procs9x6.cls; Talk presented by F. Murgia at the II International Workshop on Transverse Polarisation Phenomena in Hard Processes (Transversity 2008), May 28-31, 2008, Ferrara (Italy

General helicity formalism for Single and Double Spin Asymmetries in p p --> pion + X

We consider within a generalized QCD factorization approach, the high energy inclusive polarized process p p --> pion + X, including all intrinsic partonic motions. Several new spin and k_T-dependent soft functions appear and contribute to cross sections and spin asymmetries. We present here formal expressions for transverse single spin asymmetries and double longitudinal ones. The transverse single spin asymmetry, A_N, is considered in detail, and all contributions are evaluated numerically. It is shown that the azimuthal phase integrations strongly suppress most contributions, leaving at work mainly the Sivers effect.Comment: LaTeX, 5 pages, 1 eps figure, uses epsfig, wrapfig. Talk delivered by S. Melis at the ``XI Workshop on High Energy Spin Physics'', SPIN 05, September 27 - October 1, 2005, Dubna, Russi

Helicity Formalism and Spin Asymmetries in Hadronic Processes

We present a generalized QCD factorization scheme for the high energy inclusive polarized process, (A, S_A) + (B, S_B) -> C + X, including all intrinsic partonic motions. This introduces many non-trivial azimuthal phases and several new spin and k_T dependent soft functions. The formal expressions for single and double spin asymmetries are discussed. Numerical results for A_N[p(transv. polarized) p -> pi + X] are presented.Comment: 8 pages, 4 ps figures, uses ws-procs9x6.cls and rotating_pr.sty (included). Talk delivered by F. Murgia at the "International Workshop on Transverse Polarisation Phenomena in Hard Processes" (TRANSVERSITY 2005), September 7-10 2005, Como, Ital

Sivers effect in Drell-Yan processes

The Sivers distributions recently extracted from semi-inclusive deep inelastic scattering data [1] are used to compute estimates for Sivers asymmetries in Drell-Yan processes which are being planned at several facilities (RHIC, COMPASS, J-PARC, PAX, PANDA, NICA (JINR) and SPASCHARM (IHEP)). Most of these asymmetries turn out to be large and could allow a clear test of the predicted sign change of the Sivers distributions when active in SIDIS and Drell-Yan processes. This is regarded as a fundamental test of our understanding, within QCD and the factorization scheme, of single spin asymmetries.Comment: RevTeX4, 12 pages, 23 eps figure

Sivers distribution functions and the latest SIDIS data

We present an extraction of the Sivers distribution functions from the most recent experimental data of the HERMES and COMPASS experiments, assuming a negligible contribution of sea quark Sivers functions.Comment: To appear in the Proceedings of the XIX International Workshop on Deep-Inelastic Scattering and Related Subjects (DIS 2011), April 11-15, 2011, Newport News, VA USA. Typo corrected in Table