Professor Adam Gibson-Even
Arts and Sciences
Department of Physics and Astronomy
The Solenoidal Tracker at RHIC (STAR) located at Brookhaven National Laboratory uses longitudinally polarized proton-proton collisions to study, among other things, the gluon spin contribution to the known proton spin of 1/2 ħ. One method is to measure the longitudinal double-spin asymmetry (ALL) in the production of eta (η) and/or neutral pion (π0) particles from the longitudinally polarized proton-proton collisions. The ALL can be related to the gluon contribution to the spin of the proton. The Endcap Electromagnetic Calorimeter (EEMC) is used to detect the two photons produced from π0 or η decay, yielding the energy and location of each photon. With the data from the EEMC, we can calculate the invariant mass of the photon pairs and produce a two-photon invariant mass spectrum. The mass spectrum is fit to a combination of signal and background functions. The total number of π0 or η particles is then obtained by integrating the signal function. The asymmetry is calculated using the number of π0 or η particles resulting from the collisions of protons with different spin alignments. We also have reconstructed data to form photon and π0 candidates and stored them in data structures called trees. To ensure quality data for the eventual ALL analysis, we monitor distributions such as the reconstructed π0 mass and the number of EEMC towers hit per event. We will present the status of the π0 and η reconstruction and the quality assurance effort across two different data sets.
Lewis, Alexis; Starkenburg, Samuel; and Nielsen, Zach, "Determining Gluon Contribution to Proton Spin with STAR Endcap Electromagnetic Calorimeter Data" (2023). Summer Interdisciplinary Research Symposium. 161.