Prototyping of a New LED-based Calibration System for the ATLAS and CMS High-Luminosity Zero Degree Calorimeter Detector

To enable the determination of the reaction plane in heavy-ion collisions at the High-Luminosity Large Hadron Collider (HL-LHC), the Run 4 Zero Degree Calorimeter (HL-ZDC) designed for the ATLAS and CMS experiments at CERN includes a Reaction Plane Detector (RPD) whose performance relies on stable photomultiplier tube (PMT) responses to forward neutron signals. We addressed the challenge of disentangling the radiation damage effects of the PMT windows by developing an LED-based calibration system to pulse PMTs during the HL-LHC abort gap. I contributed to the design, fabrication, and testing of a PCB to drive the LEDs and assisted in its integration into the existing RPD geometry. Electrical validation is ongoing as the design is adapted to the spatial constraints of Run 4. Additionally, I participated in creating a test stand at UIUC and CERN to map PMT response uniformity, providing a baseline for isolating radiation-induced degradation with respect to the tube geometry. Together with the LED calibration system, this will enable in situ monitoring of PMT gain during Run 4, as well as long-term performance characterization during the entire HL heavy-ion data-taking.