Particle Detectors R&D: Dual-Readout Calorimetry for Future Colliders and MicroMegas Chambers for the ATLAS New Small Wheel Upgrade

The thesis presents selected topics on the development of particle detectors for present and future experiments in high energy physics. It is crafted on the work carried out in the three-years period, from October 2017 to October 2020, spent as a student of the XXXIII PhD Cycle in Physics of the University of Pavia and associate member of the National Institute of Nuclear Physics (INFN). The first part concerns my activity as a member of the INFN RD_FCC Collaboration for the study of physics at future circular colliders. It is dedicated to calorimeter design, both software and hardware oriented, for applications at future electron-positron circular colliders. The substantial contribution that the dual-readout calorimetry method would bring to the precision physics program envisaged has been demonstrated. Through a detailed and original work of full-simulation of the IDEA Detector calorimeter, it was shown that a dual-readout fiber calorimeter can satisfy the most stringent requirements on hadronic calorimetry, by exploiting calibration and reconstruction approaches that are unique among future detectors. Several results, such as the discrimination of the W/Z bosons by reconstructing the invariant masses of two-jet final states, were reported for the first time. It is also worth noting the development of a simulation software, based on the Geant4 toolkit, capable of reproducing the expected detector features. This software underlies future studies on the subject. A dual-readout fiber calorimeter operating at future multi-purpose experiments would require a scalable Cherenkov and scintillation light readout system and this set the recent hardware oriented research program. In particular, the use of Silicon PhotoMultipliers for the purpose was pioneered, demonstrating a substantial improvement in the collection of Cherenkov light with respect to previous prototypes, and opening up the possibility of sampling particle showers with an unprecedented granularity. Also in this case, the results obtained are original and chart the activities for next years whose path is drawn in the document. Given their importance and being ahead of the times, these activities contributed to the dawn of the IDEA Experiment. Exploiting the studies performed, the sensitivity of the IDEA Detector, coupled to the CERN future circular electron-positron collider, for Beyond-Standard-Model Axion-Like-Particles (ALPs) search was investigated. ALPs have been considered as produced in the decays of heavy Standard Model resonances and decaying into two photons. The possibility of distinguishing the weak signal with respect to the expected background has been analyzed and the result demonstrated the uniqueness of the experiment compared to the current and future probes. The second part focuses on my work as a member of the ATLAS Experiment at CERN. Together with the ATLAS-Pavia Group, I worked on the construction of MicroMegas chambers for the New Small Wheel (NSW) upgrade, a new detector to be installed in the ATLAS forward muon spectrometer. From 2017 to 2020 all the needed SM1-type MicroMegas chambers have been built in a huge collaboration among Italian Universities and INFN. The readout panels construction and testing at the University of Pavia and INFN Sezione di Pavia was described and the results found to fulfill the ATLAS requirements. In 2019, thanks to the award of an INFN Simil-Fellowship position, I joined the CERN NSW Integration Group and participated to the detector testing phase. Particular attention was given to the detector high-voltage instability problems that severely affected the first phase of the project. The origin of the high-voltage instabilities was understood thanks to a long detector characterization through irradiation at the CERN Gamma Irradiation Facility. Once an ad hoc solution was found, the monitored detector quality, as reported in the document, substantially improved.