\documentclass[12pt]{article}
\usepackage[utf8]{inputenc}
\usepackage{comment}
\usepackage[margin=1in]{geometry}

\title{Measurements of the Longitudinal Spin Structure of the Proton from STAR}
\author{STAR collaboration}
\date{}

\begin{document}

\maketitle

\noindent
How is the spin of the proton distributed among its quark, anti-quark, and gluon constituents?
The Solenoidal Tracker at the Relativistic Heavy Ion Collider (STAR) experiment probes the gluon $\Delta g (x, Q^2)$ and sea quark $\Delta \bar{u} (x, Q^2)$, $\Delta \bar{d} (x, Q^2)$ helicity distributions using collisions of longitudinally polarized protons at $\sqrt{s} = 200 \;\mathrm{GeV}$ and $\sqrt{s} = 510 \;\mathrm{GeV}$.
$\Delta g (x, Q^2)$ can be accessed through the double spin asymmetries $A_{LL}$ in gluon-dominated hard scattering processes via inclusive jet and di-jet production,
while the $W^{+/-}$ longitudinal single spin asymmetries $A_L$ are sensitive to the light quark and anti-quark polarization in the proton.

Perturbative QCD analyses including STAR jet data at $\sqrt{s} = 200 \;\mathrm{GeV}$ and mid-pseudorapidity $|\eta_\mathrm{jet}| < 1$ provided evidence for positive gluon polarization for the momentum fraction $x > 0.05$ at a hard perturbative scale $Q^2 = 10 \;\mathrm{GeV}^2$.
The STAR data on $W^{+/-}$ revealed the existence of a flavor asymmetry in the polarization of light sea anti-quarks.
Moreover, compared to inclusive jet observables, the di-jet $A_{LL}$ measurements provide a better determination of the functional form of $\Delta g (x, Q^2)$, and the measurements at higher center-of-mass energy and more forward pseudorapidities can constrain $\Delta g (x, Q^2)$ at lower $x$.

This talk will provide an overview of recent results on understanding the longitudinal spin structure of the
proton from STAR, including inclusive jet and di-jet $A_{LL}$ measurements in $p+p$ collisions at $200 \;\mathrm{GeV}$ and $510 \;\mathrm{GeV}$ and measurements of $W^{+/-}$ $A_L$ at $510 \;\mathrm{GeV}$ at mid- and intermediate-pseudorapidities.
\end{document}