The first polarized Proton Collisions at the STAR experiment at RHIC

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.