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The Solenoidal Tracker at RHIC (STAR) located at Brookhaven National Laboratory in New York uses longitudinally polarized proton-proton collisions to determine the gluon contribution to the spin of the proton. One analysis of the 2012 data set, at a proton-proton center of mass energy of 510 GeV, studies the production of neutral pions (𝜋⁰) which immediately (~10-16 s) decay into two photons. The neutral pion asymmetry, ALL, can be determined through data collected by the Endcap Electromagnetic Calorimeter (EEMC). The EEMC, positioned in an intermediate pseudorapidity range of 1 < η < 2, is able to measure the energy and position of each photon’s electromagnetic shower. By using this information as well as the angle between the photons, the two-photon invariant mass can be reconstructed. The invariant mass spectra are fitted using a skewed Gaussian plus a background function to determine the total number of 𝜋⁰s present. The 𝜋⁰ asymmetry is calculated from the number of 𝜋⁰s in collisions with different polarization directions of the colliding proton beams. The status of the measurement of ALL of the 𝜋⁰s as a function of the transverse momentum, pT, of the 𝜋⁰ will be presented.
Kovarik, Claire, "Determining pi0 A_LL from STAR 2012 Endcap Calorimeter Data" (2019). Fall Interdisciplinary Research Symposium. 127.
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