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

TL;DR

This paper reviews the transverse momentum dependent generalized parton model's application to azimuthal asymmetries in polarized proton collisions, emphasizing universality and process dependence of TMD functions with phenomenological results at RHIC.

Contribution

It provides a comprehensive phenomenological analysis of azimuthal asymmetries in polarized proton-proton collisions, highlighting the universality and process dependence of TMD functions with new results at RHIC.

Findings

Evidence for process dependence of Sivers and Collins functions

Results consistent with universality in certain kinematic regimes

Comparison of different theoretical approaches

Abstract

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.