Spin effects in large rapidity pi0 production at STAR

Abstract

Measurements by the STAR collaboration of neutral pion production at large Feynman $x$ ($x_F$) in the first polarized proton collisions at $\sqrt{s}=200$ GeV were reported previously. During the following two runs additional statistics were acquired with an improved forward calorimeter for the $\pi^0$ cross-section and analyzing power measurements. First data from $pp$ collisions at $\sqrt{s}=410$ GeV were taken during the RHIC run that ended in June, 2005. The cross section was measured at $\eta=$3.3, 3.8 and 4.0 and was found to be consistent with next-to-leading order perturbative QCD calculations. The analyzing power was found to be zero at negative $x_F$ and at positive $x_F$ up to ~0.3, then increased with increasing $x_F$. This behavior can be described by phenomenological models including the Sivers effect, the Collins effect or higher twist contributions in initial and final states. Results for the analyzing power at $\eta=$3.7 and 4.0 from all data acquired at $\sqrt{s}=200$ GeV and the status of the analysis of the $\sqrt{s}=410$ GeV data will be presented. Future upgrade plans and status will also be discussed.