Transverse polarization distribution and fragmentation functions

TL;DR

The paper surveys transverse spin physics focusing on T-odd, transverse momentum dependent distribution and fragmentation functions and their role in single-spin asymmetries. It argues that intrinsic transverse momentum can yield leading-power effects and shows how TMDs like D1T_perp and H1_perp generate observable azimuthal asymmetries, with measurements in SIDIS and DY providing access to transversity h1 and related twist-3 functions. Using a combination of formal parameterizations and a bag-model analysis of HERMES data, it interprets the sinφ asymmetry in terms of Collins-type fragmentation and transversity, suggesting first experimental information on h1 and h_L. It also highlights how weighting cross sections by transverse momentum exposes twist-3 information without 1/Q suppression, offering a practical path to map the transverse spin structure of hadrons.

Abstract

We discuss transverse polarization distribution and fragmentation functions, in particular, T-odd functions with transverse momentum dependence, which might be relevant for the description of single transverse spin asymmetries. The role of intrinsic tranverse momentum in the expansion in inverse powers of the hard scale is elaborated upon. The sin(phi) single spin asymmetry in the process e \vec{p} -> e' pi^+ X as recently reported by the HERMES Collaboration is investigated, in particular, by using the bag model.

Figures (5)

• Figure 1: The leading order contribution to the Drell-Yan process.
• Figure 3: The chiral-even, T-odd function $D_{1T}^\perp$ signals different probabilities for $q \to \Lambda(\bm k_T^{}, \pm \bm S_T) + X$.
• Figure 4: The Collins effect function $H_1^\perp$ signals different probabilities for $q(\pm \bm S_T) \to \pi(\bm k_T^{}) + X$.
• Figure 5: Kinematics of the $\sin \phi$ asymmetry in semi-inclusive deep inelastic scattering.
• Figure 6: Bag model functions $h_1$, $h_L$ and $h_L^{WW}$.