"Measurement of the neutral pion cross section in proton-proton
collisions at $\sqrt{s}=200$ GeV with PHENIX"

For the first time during the RHIC 2001--2002 run, the Relativistic
Heavy Ion Collider at Brookhaven National Laboratory was successfully
operated as polarized proton collider. The PHENIX detector triggered
$4\times10^9$ p-p events at center of mass energies of $\sqrt{s} =
200$ GeV. We report the spin-averaged neutral pion cross section measurement
in proton-proton collisions.

Our measurement provides proton-proton reference data for the study
of hadron production at high $p_T$ in heavy-ion collisions. We further
compare our results with perturbative QCD calculations \cite{aversa}
at next-to-leading order. A detailed experimental and theoretical
understanding of hadron production in proton-proton collisions is
essential not only for the heavy-ion physics program at RHIC but
also for the study of polarized proton structure in polarized proton
collisions at RHIC.

The analysis uses the electromagnetic calorimeters in the two PHENIX
central arms. A newly installed EM calorimeter trigger was essential
in the detection of neutral pions at high $p_T$. We provide a detailed
discussion of the systematic uncertainties of the measurement including
the trigger bias, detector efficiencies and background estimates.

\begin{thebibliography}
\bibitem{aversa} Using the code from: F. Aversa, P. Chiappetta,
M. Greco and J.-Ph. Guillet, Nucl. Phys. B327, 105 (1989).
\end{thebibliography}