Efforts Toward a Measurement of Longitudinal Double-spin Asymmetry, A_LL, for Neutral Pions Using STAR Endcap Calorimeter Data from Proton-Proton Collisions

The Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory provides a unique environment to study the spin structure of the proton through polarized proton-proton collisions. One of the major goals of the STAR experiment at RHIC is to understand how gluons contribute to the proton's intrinsic spin of ½ħ. One important measurement in this effort is the asymmetry, ALL, of neutral pion (π⁰) production in polarized proton collisions which can be related to the gluon’s contribution. Using data from the 2013 proton-proton collisions at √s = 510 GeV we aim to extract the ALL. Our work, in particular, focuses on two main components: determining the number of π⁰s and calculating relative luminosities across different spin states. The π⁰s decay into two photons whose energies and positions are recorded by the Endcap Electromagnetic Calorimeter (EEMC), which covers a pseudorapidity range 1.1<η<2.0. We then fit signal and background functions to the diphoton invariant mass distribution to find the number of 𝜋0s for each spin state. Another important component is the relative luminosity, which is the correction factor that accounts for the differences in luminosity across different beam helicity states. Relative luminosities are found using scaler data and spin pattern information, after identifying and removing problematic bunch crossings. We will present our results on the relative luminosities and the status of the EEMC π0 ALL measurement.