Sivers Effect in Two-Hadron Electroproduction
  The Sivers effect in single hadron semi-inclusive deep inelastic scattering (DIS) on a transversely polarized nucleon describes the modulation of the cross section with the sine of the azimuthal angle between the produced hadron's transverse momentum and the nucleon spin ($\boldsymbol{P}_h$ and $\varphi_S$ respectively). This effect is attributed to the so-called Sivers parton distribution function of the nucleon. We employ a simple phenomenological parton model to derive the relevant cross section for two-hadron production in semi-inclusive deep inelastic scattering including the Sivers effect. We show that the Sivers effect can be observed in such process as sine modulations involving the azimuthal angles $\varphi_T$ and $\varphi_R$ of both the total and the relative transverse momenta of the hadron pair. The existence of the modulation with respect to $\varphi_R$ is new. Finally, we employ a modified version of the $\tt{LEPTO}$ Monte Carlo event generator that includes the Sivers effect to estimate the size of single spin asymmetries corresponding to these modulations. We show that $\sin(\varphi_R-\varphi_S)$ modulations can be significant, especially if we impose asymmetric cuts on the momenta of the hadrons in the pairs. 
Aram Kotzinian, Hrayr H. Matevosyan and Anthony W. Thomas
hep-ph hep-ex nucl-th