Phenomenology of single spin asymmetries in p(transv. polarized)-p -> pion + X

TL;DR

This paper develops a phenomenological model incorporating transverse momentum and spin effects to explain single spin asymmetries in polarized proton-proton collisions producing pions, aligning with experimental data and offering predictions.

Contribution

It introduces a generalized factorization scheme including transverse momentum and spin-dependent fragmentation functions to describe single spin asymmetries.

Findings

The model successfully describes existing experimental data.

Explicit expression for spin asymmetry of polarized quark fragmentation.

Predictions for other processes and experimental tests are provided.

Abstract

A phenomenological description of single transverse spin effects in hadron-hadron inclusive processes is proposed, assuming a generalized factorization scheme and pQCD hard interactions. The transverse momentum, k_T, of the quarks inside the hadrons and of the hadrons relatively to the fragmenting quark, is taken into account in distribution and fragmentation functions, and leads to possible non zero single spin asymmetries. The role of k_T and spin dependent quark fragmentations -- the so-called Collins effect -- is investigated in details in p(transv. polarized)-p -> pion + X processes: it is shown how the experimental data could be described, obtaining an explicit expression for the spin asymmetry of a polarized fragmenting quark, on which some comments are made. Predictions for other processes, possible further applications and experimental tests are discussed.