Recent results of the STAR high-energy polarized proton-proton program at RHIC at BNL

TL;DR

The STAR experiment at RHIC investigates proton spin structure by measuring asymmetries in polarized proton collisions, providing new insights into gluon polarization and transverse spin effects at energies of 200-500 GeV.

Contribution

This paper reports recent experimental results on spin asymmetries in polarized proton collisions, advancing understanding of proton spin dynamics and testing QCD predictions.

Findings

Measurement of $A_{LL}$ for inclusive jets and pions at 200 GeV.

First measurement of $A_{N}$ for mid-rapidity di-jet production.

New data on transverse single-spin asymmetries for forward neutral pions.

Abstract

The STAR experiment at the Relativistic Heavy-Ion Collider (RHIC) at Brookhaven National Laboratory (BNL) is carrying out a spin physics program colliding transverse or longitudinal polarized proton beams at $\sqrt{s}=200-500 $GeV to gain a deeper insight into the spin structure and dynamics of the proton. These studies provide fundamental tests of Quantum Chromodynamics (QCD). One of the main objectives of the STAR spin physics program is the determination of the polarized gluon distribution function through a measurement of the longitudinal double-spin asymmetry, $A_{LL}$, for various processes. Recent results will be shown on the measurement of $A_{LL}$ for inclusive jet production, neutral pion production and charged pion production at $\sqrt{s}=200 $GeV. In addition to these measurements involving longitudinal polarized proton beams, the STAR collaboration has performed several important measurements employing transverse polarized proton beams. New results on the measurement of the transverse single-spin asymmetry, $A_{N}$, for forward neutral pion production and the first measurement of $A_{N}$ for mid-rapidity di-jet production will be discussed.