PDF's attached below.

Using $\pi^{0}$'s to Understand Proton Spin Structure through Polarized $p+p$ Collisions at $0.8 < \eta < 2.0$ and $\sqrt{s} = 200$ GeV at STAR

S. Place for the STAR Collaboration

Measurements of spin dependent observables at the Relativistic Heavy Ion Collider at Brookhaven National Laboratory provide unique insight into the contribution of a proton's constituents to its spin. The Solenoidal Tracker at RHIC (STAR) can be used to measure effects of the quark and gluon spins in the proton by observations of neutral pions that result from longitudinally and transversely polarized proton-proton collisions in STAR. The neutral pions ($\pi^{0}$'s) decay into two photons that can be observed in the endcap electromagnetic calorimeter in STAR. These are used to reconstruct the kinematic properties of the $\pi^0$'s and we can then look for spin asymmetries in $\pi^{0}$ production. Measurements of both the longitudinal and transverse spin asymmetries in the production of $\pi^0$'s from data taken in 2006 have made some contributions to our understanding of the structure of the proton. New data taken in 2009, in a longitudinal spin run with greater luminosity, will provide greater precision to the final results. Results from 2006 and preliminary work on 2009 data will be shown.

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Measuring Azimuthal Angular Resolution in $p^{\uparrow}+p\to jet+X$ and $p^{\uparrow}+p\to jet+\pi^{\pm}+X$ at $\sqrt{s}=500$ GeV at STAR

J. Long for the STAR Collaboration

Measurements of particle production from polarized-proton collisions at Brookhaven National Laboratory's Relativistic Heavy Ion Collider (RHIC) give insight into proton spin structure. One way to study spin effects such as those due to quark transversity or the Sivers parton distribution function is to analyze spin-dependent asymmetries in the final-state particles produced in transversely polarized-proton collisions. The large angular acceptance of the Solenoidal Tracker at RHIC (STAR) allows the reconstruction of full jets in addition to inclusive hadron production. Analyzing spin-dependent azimuthal asymmetries in $p^{\uparrow}+p\to jet+X$ and $p^{\uparrow}+p\to jet+\pi^{\pm}+X$ allows one to isolate contributions from the Sivers and Collins effects. Measuring the resolution of the relevant azimuthal angles is critical to quantifying the systematic uncertainties of the asymmetry measurements. A useful means to study the resolutions and response of the STAR detector in light of pile-up backgrounds is to embed simulated events into real zero-bias data. In 2009 and 2011 STAR collected data from polarized-proton collisions at $\sqrt{s} = 500$ GeV. These samples provide an opportunity to compare inclusive jets at 500 GeV reconstructed from real data to those from embedded simulated events. The progress of these comparison and resolution studies will be shown.

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Generating a “Clean” Sample of pi0’s and eta’s for Energy-Calibrating the STAR Endcap Calorimeter

Lauren Skiniotes for the STAR Collaboration

The Solenoidal Tracker at RHIC (STAR) detector, located at Brookhaven National Laboratory, utilizes polarized-proton collisions to explore the contributions made by sea quarks and gluons to the known proton spin. An important component of STAR is the Endcap Electromagnetic Calorimeter (EEMC), which detects, among other particles, photons produced in the pseudorapidity range 1 < eta < 2 from beam-beam collisions and measures their energy. The quality of these energy measurements depends on accurately calibrating the energy response of the EEMC. STAR has used minimum-ionizing particles (MIPs) for this calibration. An independent energy calibration method uses reconstructed neutral pions (pi0) and etas (eta) obtained, ideally, from a “clean” event sample with minimum contamination from background. By refining sample selection criteria, background is reduced, thus leaving a “clean” sample of pi0's and eta's. These “clean” samples will be used to verify the energy calibration of the EEMC obtained using MIPs.