Charge reconstruction from photomultiplier signals for the JUNO experiment

Jiangmen Underground Neutrino Observatory (JUNO) is a multi-purpose neutrino experiment under construction in South China. It will have 20 ktons of highly transparent liquid scintillator contained in an acrylic sphere surrounded by 18000 20" PMTs and 25000 3" PMTs, providing an energy resolution better than 3\% at 1 MeV. JUNO is expected to be able to resolve the neutrino mass hierarchy, significantly improve accuracy of the solar oscillation parameters and make a significant impact on other neutrino physics domains. The amount of light emitted in the liquid scintillator is proportional to the deposited energy. The light is transformed into photoelectrons which are amplified and measured by the PMTs. In order to characterize and optimize the electronic system response of PMTs, a small JUNO mock-up has been constructed at the Laboratori Nazionali di Legnaro (LNL) and calibration operations are ongoing. In this thesis, a procedure for the charge reconstruction from PMTs signals has been developed and tested reconstructing data from a 137 Cs source. Afterwards, single photon measurements from a LED source have be studied and the reconstructed charge spectrum has enabled further studies on PMT gain calculations. Finally, in order to select the same gain for all PMTs, an analysis of the gain as a function of the PMT bias voltage of the PMT has been performed and detailed results are presented in this thesis.