A_N in Single-Inclusive Particle Production from Proton-Proton Collisions

Abstract

We analyze the cause of transverse single-spin asymmetries (TSSAs) in pion and direct photon production from proton-proton (pp) collisions. Two main approaches are used to describe these observables: collinear twist-3 (CT3) factorization and the Generalized Parton Model (GPM). We argue that within the CT3 framework, the fragmentation term can describe very well TSSAs in high transverse momentum charged and neutral pion production in pp collisions at the Relativistic Heavy Ion Collider (RHIC). In addition, TSSAs in direct photon production can be a rich source of information; namely, one can cleanly access the Qiu-Sterman function, test the process dependence of the Sivers function, and distinguish between the CT3 and GPM formalisms.

Twist-3 spin Asymmetries in $\ell N \to h X$ Studied in Collinear Factorization

“…2. The corresponding spin asymmetries in hadronic collisions have been studied extensively, where so far A N for polarization in both the initial state and the final state has played the most important role -see for instance [8] for more information. It is challenging to describe the available data in pQCD [9,10,11].…”