Neutrinoless doublebeta decay is a secondorder decay process of atomic nuclei suggested by theories beyond the Standard Model. This decay would constitute the first observation of leptonnumber conservation symmetry violation in the laboratory, showing that neutrinos are their own antiparticles. The neutrinoless doublebeta decay rate depends on a Nuclear Matrix Element (NME), which is a key parameter to design experiments and fully exploit their results. Unfortunately, for each of the neutrinoless doublebeta candidate nuclides the corresponding NME presents large uncertainties. A recent publication showed a very good correlation between the matrix elements of neutrinoless doublebeta and doublegamma decay from the Double Isobaric Analog State (DIAS) of the initial doublebeta state, i.e. the state carrying the same wavefunction except for a rotation in the isospin space, into the final doublebeta state. Therefore, we could attack the lack of experimental data on the NME values by studying the twophoton decay process. The only neutrinoless doublebeta candidate for which the DIAS is known is the 48Ca isotope, which therefore constitutes the ideal study case to start with. Given the very small doublegamma decay rate expected for this nucleus, it is essential to characterize the contributions of all the competing processes and determine the optimal setup and data processing methods to maximise the doublegamma detection efficiency. For this reason a dedicated custom simulation program based on the GEANT4 framework was developed, in order to simulate the experimental setup and its response to the radiation emitted in the 48Ti nuclear deexcitation. After validating the setup and the simulation outputs, different analysis methods were implemented to suppress the decay processes competing with the doublegamma decay. Promising results concerning both the identification of the doublegamma events and the associated NME extraction were obtained, supporting the feasibility of an experiment aimed at measuring this exotic process in 48Ti. When performed, this measurement will provide the first experimental constraints on the 48Ca neutrinoless doublebeta decay NME.
Neutrinoless doublebeta decay is a secondorder decay process of atomic nuclei suggested by theories beyond the Standard Model. This decay would constitute the first observation of leptonnumber conservation symmetry violation in the laboratory, showing that neutrinos are their own antiparticles. The neutrinoless doublebeta decay rate depends on a Nuclear Matrix Element (NME), which is a key parameter to design experiments and fully exploit their results. Unfortunately, for each of the neutrinoless doublebeta candidate nuclides the corresponding NME presents large uncertainties. A recent publication showed a very good correlation between the matrix elements of neutrinoless doublebeta and doublegamma decay from the Double Isobaric Analog State (DIAS) of the initial doublebeta state, i.e. the state carrying the same wavefunction except for a rotation in the isospin space, into the final doublebeta state. Therefore, we could attack the lack of experimental data on the NME values by studying the twophoton decay process. The only neutrinoless doublebeta candidate for which the DIAS is known is the 48Ca isotope, which therefore constitutes the ideal study case to start with. Given the very small doublegamma decay rate expected for this nucleus, it is essential to characterize the contributions of all the competing processes and determine the optimal setup and data processing methods to maximise the doublegamma detection efficiency. For this reason a dedicated custom simulation program based on the GEANT4 framework was developed, in order to simulate the experimental setup and its response to the radiation emitted in the 48Ti nuclear deexcitation. After validating the setup and the simulation outputs, different analysis methods were implemented to suppress the decay processes competing with the doublegamma decay. Promising results concerning both the identification of the doublegamma events and the associated NME extraction were obtained, supporting the feasibility of an experiment aimed at measuring this exotic process in 48Ti. When performed, this measurement will provide the first experimental constraints on the 48Ca neutrinoless doublebeta decay NME.
Double$\gamma$ measurement and its implications on $0\nu\beta\beta$ decay: a feasibility study
STRAMACCIONI, DAMIANO
2022/2023
Abstract
Neutrinoless doublebeta decay is a secondorder decay process of atomic nuclei suggested by theories beyond the Standard Model. This decay would constitute the first observation of leptonnumber conservation symmetry violation in the laboratory, showing that neutrinos are their own antiparticles. The neutrinoless doublebeta decay rate depends on a Nuclear Matrix Element (NME), which is a key parameter to design experiments and fully exploit their results. Unfortunately, for each of the neutrinoless doublebeta candidate nuclides the corresponding NME presents large uncertainties. A recent publication showed a very good correlation between the matrix elements of neutrinoless doublebeta and doublegamma decay from the Double Isobaric Analog State (DIAS) of the initial doublebeta state, i.e. the state carrying the same wavefunction except for a rotation in the isospin space, into the final doublebeta state. Therefore, we could attack the lack of experimental data on the NME values by studying the twophoton decay process. The only neutrinoless doublebeta candidate for which the DIAS is known is the 48Ca isotope, which therefore constitutes the ideal study case to start with. Given the very small doublegamma decay rate expected for this nucleus, it is essential to characterize the contributions of all the competing processes and determine the optimal setup and data processing methods to maximise the doublegamma detection efficiency. For this reason a dedicated custom simulation program based on the GEANT4 framework was developed, in order to simulate the experimental setup and its response to the radiation emitted in the 48Ti nuclear deexcitation. After validating the setup and the simulation outputs, different analysis methods were implemented to suppress the decay processes competing with the doublegamma decay. Promising results concerning both the identification of the doublegamma events and the associated NME extraction were obtained, supporting the feasibility of an experiment aimed at measuring this exotic process in 48Ti. When performed, this measurement will provide the first experimental constraints on the 48Ca neutrinoless doublebeta decay NME.File  Dimensione  Formato  

Stramaccioni_Damiano.pdf
accesso riservato
Dimensione
4.36 MB
Formato
Adobe PDF

4.36 MB  Adobe PDF 
The text of this website © Università degli studi di Padova. Full Text are published under a nonexclusive license. Metadata are under a CC0 License
https://hdl.handle.net/20.500.12608/51909