The first polarized Proton Collisions at the STAR experiment at RHIC

TL;DR

The STAR experiment at RHIC successfully conducted the first polarized proton collisions, measuring the single transverse spin asymmetry for forward π0 production, marking a significant step in understanding proton spin structure.

Contribution

This paper reports the first polarized proton collision results at RHIC, introducing new detector components for asymmetry measurements in proton spin studies.

Findings

First measurement of $A_N$ for forward $b0$ production at RHIC

Implementation of new forward $b0$ detector system

Successful background suppression and luminosity measurement

Abstract

The first run of transverse polarized protons at RHIC was recently completed which opened a new era exploring the spin structure of the proton. A first measurement of the single transverse spin asymmetry, $A_{N}$, for leading $\pi_{0}$ production from transverse colliding polarized protons at $\sqrt(s)=200 $GeV, $X_{F}>0.25$ and $p_{T}\simeq 1-4 $GeV was a focus of the STAR collaboration during the first polarized proton run at RHIC. Two new subcomponents have been added to the STAR experiment to carry out such a measurement in polarized proton collisions: a forward $\pi_{0}$ detector system at approximately $7.8 $m of the STAR interaction region to reconstruct $\pi_{0}$ mesons from their decay products $(\pi_{0}\to \gamma\gamma)$ and a beam-beam counter with large forward acceptance to provide a means of beam-related background suppression and relative luminosity measurement.