Do we understand the single-spin asymmetry for p i 0 inclusive production in pp collisions?
Abstract
The cross section data for
π
0
inclusive production in
pp
collisions is considered in a rather broad kinematic region in energy
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.