Characterization of the CYGNO experiment prototype during the underground campaign at LNGS

The CYGNO collaboration is a dedicated research group with a primary focus on establishing a high-resolution Time Projection Chamber (TPC) employing optical readout through gas electron multipliers (GEMs) at the INFN Gran Sasso Laboratories (LNGS). Its innovative setup consists of a helium/fluorine gas mixture at atmospheric pressure and the use of a CMOS camera and fast photomultiplier tubes (PMTs) for directional Dark Matter search and solar neutrino spectroscopy. The goal is to achieve a 3D tracking, with head tail capability, and background rejection down to O(keV) energy, in order to explore the O(GeV) mass range both for SI and SD coupling. During my thesis project, I actively participated in the underground commissioning of the LIME detector of the CYGNO experiment at LNGS. This prototype, which featured a 50-liter detector equipped with an sCMOS camera and four PMTs, plays a pivotal role in validating the project's scalability. Throughout my thesis work, I had the privilege of gaining hands-on experience across various research aspects, encompassing technical aspects of the prototype and extensive data analysis. From the PMT perspective, my main contribution included conducting an initial assessment of the diffusion coefficient of ionized electrons in the gas mixture, specifically along the direction parallel to the drift field. Subsequently, my focus shifted towards integrating PMT and camera data to achieve a comprehensive 3D reconstruction of particle tracks within the detector. To facilitate this integration, I curated a clean dataset of events where the association between camera and PMT data was unambiguous. This dataset proved invaluable for a thorough examination and optimization of the experiment's reconstruction algorithms. In addition to these tasks, I engaged in the critical challenge of distinguishing between the signatures of electronic recoil (ER) and nuclear recoil (NR) events. Specifically, I conducted a comparative analysis between two dataset, one of which had a high rate of nuclear scattering events through the use of an external source of Americium-Beryllium. In the context of dark matter research, the ER/NR discrimination is paramount, as only the latter events provide information suggestive of a possible presence of Weakly Interacting Massive Particles (WIMPs).