Sivers asymmetry for the proton and the neutron

A puzzling experimental scenario has arisen recently, after measurements of semi-inclusive deep inelastic scattering (SIDIS) off transversely polarized proton and deuteron targets [1]. A formalism will be described aimed at evaluating the Sivers function entering single spin asymmetries [2]. The approach is well suited for calculations which use constituent quark models to describe the structure of the nucleon. As an example, the Sivers function is evaluated using the Isgur-Karl model. The results are consistent with a sizable Sivers effect, with an opposite sign for the u and d flavors. Although a consistent QCD evolution of the results from the momentum scale of the model to the experimental one is not yet possible, an estimate shows that a reasonable agreement with the available data is obtained once the evolution of the model results is performed. Besides, with the aim at extracting the neutron information, a measurement of SIDIS off polarized 3He has been addressed [3], and two experiments are forth-coming at JLab [4]. An impulse approximation analysis of SIDIS for the production of leading pions off transversely polarized 3He will be summarized [5]. The AV18 interaction is used for a realistic description of the nuclear dynamics, and the nucleon structure is described by parameterizations of data or suitable model calculations. The crucial issue of extracting the neutron information from 3He data will b