WAQAS, Muhammad (2025) Design and Characterization of a multiPMT Photo-Detector System for the SWGO Experiment. [Tesi di dottorato]

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Abstract

The "Southern Wide-Field Gamma-ray Observatory" (SWGO) is a pioneering project designed to advancegamma-ray astronomy by deploying an array of Water Cherenkov Detectors (WCDs) at Pampa La Bola, in the Atacama Astronomical Park, Chile, at an altitude of 4770 meters and a latitude of approximately 23° south. This observatory will contribute to significant discoveries in astrophysics, such as studying cosmic ray acceleration mechanisms and gamma-ray bursts, by detecting high-energy gamma rays from cosmic sources. The detection principle is based on Cherenkov radiation emitted by high-energy particles traveling faster than the speed of light in water, with Photomultiplier Tubes (PMTs) capturing this light to analyze particle properties. A critical challenge for SWGO is balancing cost and performance while main- taining high efficiency and strong background rejection to differentiate between gamma-ray and hadronic showers. Efficient background rejection is essential for increasing sensitivity to gamma rays and enabling precise measurements of cosmic sources. To address these challenges, the Napoli SWGO group propose adopting the Optical Module concept pioneered by the KM3NeT collaboration. This novel design replaces traditional large-area PMTs with multi-PMT modules, consisting of smaller 3-inch PMTs housed in a pressure-resistant vessel. This technology offers enhanced granularity, improved timing and spatial resolution, and superior directional sensitivity, all of which are critical for reconstructing particle events and tracing cosmic gamma rays back to their sources. Our contribution focuses on evaluating the impact of this multi-PMT design on SWGO's performance. Our simulation analyses demonstrate that the multi-PMT modules significantly improve the observatory's ability to tag muons and separate tanks hit by a muon from those containing only the electromagnetic components of the shower. This enhanced muon-tagging capability refines gamma-ray event separa- tion from the hadronic background, boosting the detector's sensitivity to astrophysical gamma rays. Additionally, the design optimizes efficiency by improving timing resolution and directional accuracy, critical for event reconstruction and source identification. The multi-PMT modules undergo rigorous testing under operational condi- tions before integration into the WCD tanks. These tests validate their functionality and ensure reliability in the high-altitude environment of the observatory. Optimized placement of these modules further enhances the overall performance of SWGO. In summary, the multi-PMT design enhances timing resolution, directional sensitivity, and reconstruction performance, ensuring greater efficiency and reliability for SWGO. These advancements, supported by simulations and testing, will enable groundbreaking contributions to high-energy astrophysics.

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