Double Helicity Asymmetry in Inclusive Mid-Rapidity neutral pion Production for Polarized p+p Collisions at sqrt(s)=200 GeV

TL;DR

This paper reports the first measurement of the double helicity asymmetry in inclusive neutral pion production in polarized proton-proton collisions at 200 GeV, providing insights into the proton's spin structure.

Contribution

It presents the first experimental measurement of double helicity asymmetry in pi^0 production at collider energies, testing NLO pQCD predictions and polarized gluon distributions.

Findings

Asymmetry is small across the measured pT range.

Results are consistent with certain polarized gluon distribution models.

Provides new data for understanding proton spin structure.

Abstract

We present a measurement of the double longitudinal spin asymmetry in inclusive pi^0 production in polarized proton-proton collisions at sqrt(s)=200 GeV. The data were taken at the Relativistic Heavy Ion Collider with average beam polarizations of 26%. The measurements are the first of a program to study the longitudinal spin structure of the proton, using strongly interacting probes, at collider energies. The asymmetry is presented for transverse momenta 1-5 GeV/c at mid-rapidity, where next-to-leading order perturbative quantum chromodynamic (NLO pQCD) calculations describe the unpolarized cross section well. The observed asymmetry is small and is compared with a NLO pQCD calculation with a range of polarized gluon distributions.