Longitudinal Spin Measurements with Inclusive Hadrons in Polarized p+p Collisions at 200 GeV

TL;DR

This paper reports measurements of gluon polarization in protons using inclusive hadron production in polarized proton-proton collisions at 200 GeV, providing constraints on the gluon polarization but with limited statistical precision.

Contribution

First measurement of double longitudinal spin asymmetries for inclusive pi0 and pi+(-) production at RHIC, constraining gluon polarization in the proton.

Findings

Measured asymmetries disfavor large positive gluon polarization.

Results agree with NLO pQCD calculations for unpolarized cross sections.

Data provide constraints but do not definitively determine gluon polarization.

Abstract

We present measurements of the double longitudinal spin asymmetries for inclusive pi0 and pi+(-) production in polarized p+p collisions at sqrt(s) = 200 GeV at mid-rapidity with the STAR detector from the 2005 RHIC run. These measurements are used to access Delta G/G, the gluon polarization in the proton. The observed unpolarized inclusive cross sections show good agreement with NLO pQCD calculations. The double longitudinal spin asymmetries are compared to NLO pQCD calculations based on different assumptions for the gluon polarization in the nucleon to provide constraints on Delta G/G. At the present level of statistics the measured asymmetries disfavor a large positive gluon polarization, but cannot yet distinguish between other scenarios.