STAR results on longitudinal spin dynamics

TL;DR

This paper reports preliminary measurements of spin asymmetries in jet and hyperon production at RHIC, providing insights into the gluon polarization within the nucleon and showing results consistent with existing models.

Contribution

First measurements of double longitudinal spin asymmetries in inclusive jet and hyperon production at RHIC, constraining gluon polarization models.

Findings

Jet asymmetries are consistent with small or zero gluon polarization.

Hyperon spin transfer asymmetries are consistent with zero.

Results disfavor large positive gluon polarization.

Abstract

We present preliminary results on the double longitudinal spin asymmetries A_LL in inclusive jet production and the longitudinal spin transfer asymmetries D_LL in inclusive Lambda and anti-Lambda hyperon production. The data amount to about 0.5 pb-1 collected at RHIC in 2003 and 2004 with beam polarizations up to 45 %. The jet A_LL asymmetries, measured over 5 < pT < 17 GeV/c, are consistent with evaluations based on deep-inelastic scattering parametrizations for the gluon polarization in the nucleon, and disfavor large positive values of gluon polarization in the nucleon. The Lambda and anti-Lambda D_LL, measured at midrapidity and at low average transverse momentum of 1.5 GeV/c, are consistent with zero within their dominant statistical uncertainties.