Cosmic Ray Testing of the New sPHENIX Event Plane Detector

sPHENIX is a state-of-the-art detector currently under construction at Brookhaven National Laboratory. It will study strongly interacting quark gluon plasma using jet and heavy-flavor observables. A crucial part of the sPHENIX design is the Event Plane Detector (sEPD), which measures the orientation of charged particles emitted at small angles with respect to the particle beam line. It consists of two wheels of scintillator made of 12 sectors, with each sector divided into 31 tiles. Each of these tiles requires extensive testing to look at qualities such as tile isolation, uniformity, and efficiency. To test for tile efficiency, I set up a cosmic ray test stand using a leading edge discriminator and pairs of paddle scintillators connected to photomultiplier tubes as the trigger. This test requires a muon coincidence, which indicates a muon passed through both paddles, and therefore the sEPD tile placed in between them. The light output of each sEPD tile is read via a silicon photomultiplier and optical fibers connected to an oscilloscope. The distribution of this voltage is then analyzed.