Faculty Sponsor

Professor Adam Gibson-Even


Arts and Sciences


Physics and Astronomy

Presentation Type

Poster Presentation

Symposium Date

Summer 7-23-2021


The spin of the proton is known to be 1/2 $\hbar$. It derives from the spin and orbital angular momenta of the proton’s constituents: quarks and gluons. The relative contribution of the various components remains uncertain, with the quark spin contribution significantly lower than once anticipated. We seek to clarify the gluon spin contribution, in particular. At the STAR experiment at Brookhaven National Laboratory (BNL) we observe collisions between spin-polarized beams of protons. In this measurement, our probe of collisions with initial-state gluons will be the neutral pion ($\pi^0$), abundantly produced in such collisions. The $\pi^0$s rapidly decay into two photons, which we can detect with STAR’s Endcap Electromagnetic Calorimeter (EEMC). We have been calibrating and reconstructing the 2013 data to form both photon and $\pi^0$ candidates and storing this information in data structures called trees. The $\pi^0$’s invariant mass is calculated from the two photons using their energies and opening angle. We will eventually fit the invariant mass spectrum to separate signal and background contributions and calculate the number of $\pi^0$s produced. With the number of $\pi^0$s for each spin combination, we will then calculate the $A_{LL}$, the doubly longitudinal spin asymmetry, for $\pi^0$ production in the EEMC. We track the reconstruction process and assure its quality. We will describe our efforts to identify bad data using $\pi^0$ mass distributions and quantities including a calculated signal fraction. We will present the status of the 2013 EEMC $\pi^0$ dataset and our quality assurance analysis.