Supernova neutrino detection in JUNO, a large liquid scintillator neutrino detector

The Jiangmen Underground Neutrino Observatory (JUNO) is a multi-purpose neutrino experiment under construction in South China. The 20 kton of highly transparent Liquid Scintillator (LS) are contained in an acrylic sphere surrounded by 17612 20” PhotoMultiplier Tubes (PMTs) and 25600 3” PMTs. JUNO aims at providing an energy resolution better than 3% at 1 MeV and thus offers exciting opportunities for addressing various important topics in neutrino and astroparticle physics. For instance, neutrinos play a crucial role during all stages of stellar collapse and explosion. The signature of a supernova explosion is a sudden increase of the neutrino interaction rate in the detector of several orders of magnitude (from below 1 kHz up to 1 MHz) for a short time O(1 s). Therefore the readout electronics has to withstand very high rates for a limited amount of time without data losses. The JUNO Padova research group is responsible for the design and development of the large PMTs readout electronics. The PMTs output signal is processed and stored temporarily in a local memory before being sent to the data acquisition, once validated by the trigger electronics. Besides the local memory situated in the readout-board FPGA, a 2 GBytes DDR3 SDRAM memory is available and it is used to provide a larger memory buffer in the exceptional case of a sudden increase of the input rate. A small experiment with 48 small size PMTs reading out the light coming from a 20 liter LS detector has been assembled at the Legnaro National Laboratories in Legnaro, Italy. Another setup has been built at the Institute of High Energy Physics in Beijing, China. The first part of the thesis concerns the performance assessment of the electronics, carried out by simulating the production of high-rate scintillation photons in the LS and testing the highest rates sustainable by the system. By retrieving the amount of expected events and the number of correctly read events, it is possible to compute the efficiency of the setup at a fixed rate. This made it possible to understand the rate range in which the system can work and when the DDR3 is necessary. Finally, rate measurements employing exclusively the DDR3 memory were collected thanks to a third setup at the Department of Physics and Astronomy in Padua, Italy. The purpose of this test is to understand whether the memory is capable of storing all the useful high-rate events by overrunning the usual data transfer bandwidth between the read-out electronics and the DAQ.