Longitudinal double-spin asymmetry and cross section for inclusive neutral pion production at midrapidity in polarized proton collisions at sqrt(s) = 200 GeV

TL;DR

This paper measures the double-spin asymmetry and cross section for inclusive neutral pion production in polarized proton collisions at 200 GeV, providing insights into gluon polarization and testing perturbative QCD predictions.

Contribution

It presents the first measurement of A_LL and cross sections for Pi0 production at this energy, constraining gluon polarization in the proton.

Findings

Cross section agrees with next-to-leading order pQCD

Excludes maximal positive gluon polarization

Pi0s carry about 70% of parent jet momentum

Abstract

We report a measurement of the longitudinal double-spin asymmetry A_LL and the differential cross section for inclusive Pi0 production at midrapidity in polarized proton collisions at sqrt(s) = 200 GeV. The cross section was measured over a transverse momentum range of 1 < p_T < 17 GeV/c and found to be in good agreement with a next-to-leading order perturbative QCD calculation. The longitudinal double-spin asymmetry was measured in the range of 3.7 < p_T < 11 GeV/c and excludes a maximal positive gluon polarization in the proton. The mean transverse momentum fraction of Pi0's in their parent jets was found to be around 0.7 for electromagnetically triggered events.