Do we understand the single-spin asymmetry for π0 inclusive production in pp collisions?

The cross section data for pi(0) inclusive production in pp collisions is considered in a rather broad kinematic region in energy roots, Feynman variable x(F) and transverse momentum p(T). The analysis of these data is done in the perturbative QCD framework at the next-to-leading order. We find that they cannot be correctly described in the entire kinematic domain and this leads us to conclude that the single-spin asymmetry, A(N) for this process, observed several years ago at FNAL by the experiment E704 and the recent result obtained at BNL-RHIC by STAR, are two different phenomena.