| dc.description.abstract | We are living a pivotal moment for neutrino physics. A new generation of experiments is
about to begin and will extend our understanding of neutrinos. Very large scale experiments,
like Hyper-Kamiokande, will collect unprecedented statistics and will constrain oscillation parameters
to high precision: the CP violation phase, the octant of 23, and the mass hierarchy
are likely to be determined. Many are the experimental difficulties behind a successful megaton
water Cherenkov detector, but improvements in photodetection technologies luckily allow such
an ambitious project. One of the most important challenges is to keep systematical uncertainties
under control, so as they do not dominate over statistical errors. Assessing the impact of
the systematics on the overall sensitivity of the experiment is a fundamental requirement to the
final success of Hyper-Kamiokande.
Thanks to powerful accelerator facilities, future long baseline experiments, such as DUNE,
will also explore the intensity frontier of neutrino physics and study rare phenomena. Numerous
extension to the Standard Model (SM) and alternative theories have been introduced to explain
neutrino masses and mixings. These new scenarios often predict new physics, the signature of
which is accessible to next-generation experiments. An interesting example comes from lowscale
see-saw models, which consider GeV-scale neutral leptons coupled to SM particles with
suppressed mixing angles. The near detector system of DUNE is an ideal place for searches of
these particles, thanks to high exposure that compensate small event rates.
Current neutrino experiments have also joined this new venture; Super-Kamiokande has been
extensively refurbished in view of a new phase, starting in early 2020, in which the detector will
turn into a supernova observatory. This is achieved by doping the water of Super-Kamiokande
with gadolinium, in order to increase the efficiency of neutron tagging up to 90 %. The use of
gadolinium is a novel technique which will be adopted by many existing and planned experiments.
The benefits of improved neutron tagging are not limited just to supernova neutrinos,
but to a plethora of other studies, such as reactor and atmospheric neutrinos or proton decay.
In this thesis, all of the topics above are addressed. After a review of SM neutrino physics
in Chapter 1, the gadolinium-loaded water Cherenkov technique is discussed in Chapter 2 with
particular focus on Super-Kamiokande. A new technique to monitor gadolinium concentration
in water using UV spectroscopy and an improved method for neutron calibration using a californium
source are presented. Chapter 3 deals with CP violation in neutrino oscillation and the
potential of Hyper-Kamiokande to constraining oscillation parameters. The methodology used
to asses the experimental sensitivity is described in detail. First estimations are shown with
the full systematic model and some of its variations are also taken into account. In Chapter 4
a possible Standard Model extension to explain neutrino masses is considered, and the phenomenology
of such models is extensively studied in the context of a beam dump experiment.
The prospect of the DUNE’s near detector to searches of heavy neutral lepton decays is then
evaluated in Chapter 5. It is found that the DUNE ND is capable of extending current limits on
these searches, reaching regions of the parameter space extremely interesting from a theoretical
point of view. | en_US |
