Abstract
We review and give an update on the current status of what causes transverse single-spin asymme- tries (TSSAs) in semi-inclusive processes where a single hadron is detected in the final state, especially those involving proton-proton (pp) collisions. In particular, we provide a new analysis within collinear factorization of TSSAs in high transverse momentum charged and neutral pion production in ppcollisions at the Relativistic Heavy Ion Collider (RHIC). This study incorporates the so-called twist-3 fragmentation term and shows that one can describe RHIC data through this mechanism. Moreover, by fixing other non-perturbative inputs through extractions of transverse momentum dependent functions in e + e − → h1h2X and semi-inclusive deep-inelastic scattering (SIDIS), we provide for the first time a consistency between certain spin/azimuthal asymmetries in all three reactions (i.e., pp, e + e − , and SIDIS).
Highlights
We consider a process of the type A(P, S ⊥) + B(P ) → C(Ph) + X, where the 4-momenta and polarizations of the incoming protons A, B and outgoing hadron C are specified
There are several non-perturbative functions that enter into Eq (3). They are the transversity distribution h1, the unpolarized parton density f1, and the three fragmentation functions (FFs) H, H, and H FU, with the last one being the imaginary part of a 3-parton correlator
Collinear twist-3 QCD factorization can be considered the most natural and rigorous approach to describe this observable, yet the sign-mismatch issue [25] threatened the validity of this formalism
Summary
We consider a process of the type A(P, S ⊥) + B(P ) → C(Ph) + X, where the 4-momenta and polarizations of the incoming protons A, B and outgoing hadron C are specified. For the third term in (1), in which collinear twist-3 functions enter for the outgoing (unpolarized) hadron, the complete analytical result was obtained only recently [21]. There are several non-perturbative functions that enter into Eq (3) They are the transversity distribution h1, the unpolarized parton density f1, and the three (twist-3) fragmentation functions (FFs) H , H, and H FU, with the last one being the imaginary part of a 3-parton correlator. Implying that in the collinear twist-3 framework one has two independent FFs. It is important to realize that this is different from the so-called TMD approach for AN, where only H1⊥ enters the fragmentation piece [42]. The collinear twist-3 formalism is the more rigorous theoretical framework
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