The GERDA experiment at the Gran Sasso underground laboratories is searching for neutrinoless
double-beta decay in 76 Ge. In order to observe such a rare process this experiment will collect an exposure
of 100 kg·y in background free condition. In 2018 many upgrades have been performed on the apparatus.
In my thesis project I am studying and modeling the full-range energy spectrum acquired by the germanium
detectors. All the analysis is done using bayesian statistics approach (parameter estimation, hypothesis
testing, etc.). The spectrum is modeled by means of Monte Carlo simulations reproducing possible ra-
dioactive isotopes, coming from U and T h chains or from cosmogenic activation, distributed in different
components of the apparatus (cables, LAr, etc.) that can give significant contribution. The parameters
of interest (isotopes activities, two neutrino beta decay’s half life) are then estimated from the data using
Markov Chain Monte Carlo algorithms while direct screening measurements of the apparatus’ components
(if available) are introduced as prior distributions in the analysis. For very high statistics gamma decay
lines ( 40 K and 42 K) a detector by detector study of the number of registered counts is performed in order
to get a more accurate and reliable assessment of the activities of the isotope generating these events; then
they are inserted as prior distributions in the full-range fit.
From this analysis it will be possible to understand the origin of the collected events, make a precise mea-
surement of the half-life of the allowed two neutrino decay mode and could also give information about the
purity of the materials for future experiments’ strategies. Moreover this study will help a lot the search
for the neutrinoless double-beta decay in the region around Q ββ
