Azimuthal asymmetries for hadron distributions inside a jet in hadronic collisions

TL;DR

This paper investigates azimuthal asymmetries in hadron distributions within jets produced in hadronic collisions, using a generalized parton model to analyze spin and intrinsic motion effects, with predictions relevant for RHIC experiments.

Contribution

It provides a comprehensive analysis of azimuthal asymmetries in jet fragmentation, including all relevant TMD functions and their potential maximal effects at RHIC energies.

Findings

Identifies leading-twist azimuthal asymmetries for unpolarized and polarized cases.

Evaluates potential asymmetries by saturating positivity bounds for TMD functions.

Estimates asymmetries for pions at RHIC kinematics.

Abstract

Using a generalized parton model approach including spin and intrinsic parton motion effects, and assuming the validity of factorization for large-pT jet production in hadronic collisions, we study the azimuthal distribution around the jet axis of leading unpolarized or (pseudo)scalar hadrons, namely pions, produced in the jet fragmentation process. We identify the observable leading-twist azimuthal asymmetries for the unpolarized and single-polarized case related to quark and gluon-originated jets. We account for all physically allowed combinations of the transverse momentum dependent (TMD) parton distribution and fragmentation functions, with special attention to the Sivers, Boer-Mulders, and transversity quark distributions, and to the Collins fragmentation function for quarks (and to the analogous functions for gluons). For each of these effects we evaluate, at central and forward rapidities and for kinematical configurations accessible at BNL-RHIC, the corresponding potentially maximized asymmetry (for pi+ production), obtained by saturating natural positivity bounds (and the Soffer bound for transversity) for the distribution and fragmentation functions involved and summing additively all partonic contributions. We then estimate, for both neutral and charged pions, the asymmetries involving TMD functions for which parameterizations are available. We also study the role of the different mechanisms, and the corresponding transverse single spin asymmetries, for large-pT inclusive jet production.