Recent STAR Results from Charged Pion Production in Polarized pp Collisions at $\sqrt{s} = 200 GeV$ at RHIC

TL;DR

This paper reports recent measurements of the double-spin asymmetry and cross section ratios for charged pion production in polarized proton collisions at RHIC, providing insights into the polarized gluon distribution within the proton.

Contribution

It presents new measurements of $A_{LL}$ for charged pions and the ratio of $^-$ to $^+$ cross sections, advancing understanding of proton spin structure.

Findings

Measured $A_{LL}$ for charged pions at $.2$

Determined the ratio of $^-$ to $^+$ cross sections

Provided data constraining the polarized gluon distribution

Abstract

The STAR experiment at RHIC measures the longitudinal double-spin asymmetry $A_{LL}$ for a variety of final states in collisions of longitudinally polarized protons to constrain the polarized gluon distribution in the proton. Asymmetries for mid-rapidity charged pion production benefit from large cross-sections and the excellent tracking and particle identification capabilities of the STAR Time Projection Chamber. This contribution presents a measurement of the ratio of cross sections for inclusive $\pi^{-}$ and $\pi^{+}$ production using data collected in 2005, as well as a new measurement of $A_{LL}$ for charged pions opposite a jet obtained from the 2006 RHIC run.