Lavitola, Luigi (2024) Development and optimization of detector and electronics system for Hyper-Kamiokande. [Tesi di dottorato]

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Abstract

Neutrino physics plays a crucial role in understanding our universe. In the last centuries many important experiments focused their attention on neutrinos. Those are characterized by a very small mass (indeed they are massless for the Standard Model) and no electric charge. They interact only through weak interactions, making them even more difficult to detect. In the last decades, one of the country that contributed with some of the most impotant results in this field is Japan, thanks to the Kamiokande and Super-Kamiokande experiment, both of them recognized with a Nobel Prize, both hosted by Japanese institutions. Hyper-Kamiokande (Hyper-K) is the next generation of large-scale water Cherenkov detector in Japan. With a volume an order of magnitude bigger than its predecessor Super-Kamiokande (Super-K) and improved photosensors’ system and beam-line, Hyper-K aims to obtain exciting results in many fields such as the study of CP violation in the leptonic sector, the search for proton decay and the study of atmospheric neutrinos and neutrinos from astronomical origin. For the Hyper-K far detector the collaboration decided to adopt a hybrid configuration that combines the 20" PMTs, already adopted in Super-K but improved with a better performance, with the multi-PMT (mPMT) modules, a novel technology first designed for the KM3NeT experiment. This detector consists in a number of 3" PMTs inside a vessel, each one with a different orientation. A big improvement in the event reconstruction is expected with this solution, especially thanks to an improved directional sensitivity, better timing and energy resolutions and an overall lower dark rate. The electronics systems for the two photosensor systems are the aim and the result of this work, in particular the development of the final version of the electronics for the mPMT system and the development of a novel proposal for the 20" PMTs digitizer system, that is also now in the final stages of the R&D. Also, a combination of the two electronics has been adopted as the main point for the development of the Front End for the Outer Detector 3” PMTs that will be mainly used as veto. This work is organized as follows: • A brief introduction to neutrino physics is given in the first chapter, with a description of the principal experimental results in the sector, in particular on the investigation of leptonic CP violation and to the study of neutrinos from supernovae. • The second chapter is dedicated to an introduction to Hyper-K experiment, 4 in particular a description of the detector and its capability in the various different fields where it will be important. A brief introduction and descrip- tion of a test experiment at CERN, called WCTE (Water Cherenkov Test Experiment) will also be provided, since we will see that this test will be the final test before mass production for the proposed new mPMT detector in Hyper-K. • The third chapter describes the Hyper-K photosensors, both the 20" PMT and the mPMT. We discuss the main characteristics of the photosensors and the improvements to the physics capabilities in Hyper-K, in particular for the mPMT. • In the forth chapter we will describe a general overview of the Electronics in the experiment and also a brief description of the Data Acquisition and timing system will follow. • The fifth chapter describes the mPMT as a whole detector. We will focus mainly on the electronics system for the mPMT and its development, but also the mechanics and all the prototypes developed in the years will be described. We will see that now the detector is basically ready for the mass production of the experiment which will start in early 2025. • The sixth chapter is dedicated to the development of the 20" PMT electron- ics system. The work is focused on the development of the digitizer, that acquires the PMT signals to produce digital signals for charge and time measurements. Also this system is now basically ready for mass production, with the planned schedule to start the electronics assembly by the end of 2025. • The seventh chapter is dedicated to the future application of the work de- veloped in this work. In particular we will focus on the development of a mPMT detector for another experiment that is now in the R&D phase, the Southern Wide-field Gamma-ray Observatory (SWGO), that will be the largest gamma ray observatory built and will observe the southern sky of the planet. This work has been realized in collaboration with the electronic workshop of the Naples INFN section. The systems developed in this work will be the core of the whole detection and acquisition system for the Hyper-K experiment, that hopefully will lead the neutrino physics for the next couple of decades. Part of this work is also of interest of another experiment, SWGO, which will also lead the gamma ray observation in the south hemisphere for the next decades.

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