  The cross section data for $\pi^0$ inclusive production in $pp$ collisions is
considered in a rather broad kinematic region in energy $\sqrt{s}$, 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. This suggests that
STAR data probes a genuine leading-twist QCD single-spin asymmetry for the
first time and finds a large effect.
