The Sivers mechanism for the single-spin asymmetry in unpolarized lepton scattering from a transversely polarized nucleon is driven by the orbital angular momentum carried by its quark and gluon constituents, combined with QCD final-state interactions. Both quark and gluon mechanisms can generate such a single-spin asymmetry, though only the quark mechanism can explain the small single-spin asy...

We consider the double-spin cosφ asymmetry for pion electroproduction in semi-inclusive deep inelastic scattering of longitudinally polarized leptons off longitudinally polarized protons. We estimate the size of the asymmetry in the approximation where all twist-3 interaction-dependent distribution and fragmentation functions are set to zero. In that approximation at HERMES kinematics a sizable...

In the studies of semi-inclusive charged and neutral pion production off a longitudinally polarized protons, the HERMES collaboration has observed a single target-spin asymmetry (SSA) [1]. This asymmetry could either result from twist-3 chiral-odd effects [2,3] and/or could be a reflection of the Collins effect [4]. Which of the two is relevant is an open issue. For a further understanding of “...

Acceleration of polarized protons in Relativistic Heavy Ion Collider (RHIC) provides unique tool to study the spin structure of the nucleon. We give a brief overview of the PHENIX program to investigate poorly known gluon and flavor decomposed see quark polarization in the proton, utilizing polarized proton collisions at RHIC. We report PHENIX first results on transverse single-spin asymmetry i...

We report a measurement of the asymmetry in spin-dependent quasielastic scattering of longitudinally polarized electrons from a polarized 3 ~ e target. The neutron magnetic form factor G';, has been extracted from the measured asymmetry based on recent PWIA calculations using spin-dependent spectral functions. Our determination of G& at ~ ~ = 0 . 1 9 (G~VIC)' agrees with the dipole parametrizat...

We discuss transversity distributions and Drell-Yan transverse double spin asymmetries. First, the antiquark flavor asymmetry ∆ T ¯ u/∆ T ¯ d is discussed by using two different descriptions, a meson-cloud model and a Pauli exclusion model. We find that both calculations produce a significant ∆ T ¯ d excess over ∆ T ¯ u. Next, we study its effects on the transverse spin asymmetry A T T and on t...

We discuss the two-photon exchange contribution to observables which involve lepton helicity flip in elastic lepton-nucleon scattering. This contribution is accessed through the spin asymmetry for a lepton beam polarized normal to the scattering plane. We estimate this beam normal spin asymmetry at large momentum transfer using a parton model and we express the corresponding amplitude in terms ...

We calculated two–photon exchange effects for elastic electron–proton scattering at high momentum transfers. The corresponding nucleon Compton amplitude is defined by two space–like virtual photons that appear to have significant virtualities. We make predictions for a) a single–spin beam asymmetry, and b) a single–spin target asymmetry or recoil proton polarization caused by an unpolarized ele...

We analyze the spin asymmetry for single inclusive jet production in proton-proton collisions collected by the AnDY experiment at the Relativistic Heavy Ion Collider and the Sivers asymmetry data from semi-inclusive deep inelastic scattering experiments. In particular, we consider the role color gauge invariance plays in determining the process dependence of the Sivers effect. We find that afte...