Why is the observable Universe today made of matter, without any significant amount of antimatter? Neutrinos shed light on this cosmic mystery.
In 2020, the T2K collaboration in Japan published in the journal Nature [1] new results leading to the best constraint to date on the parameter dCP, which translates in the theory the degree of asymmetry between matter and antimatter. The T2K results exclude for the first time nearly half of the possible values at 99.7% (3s) and the value most compatible with the data is very close to -90° corresponding to a maximum asymmetry between matter and antimatter. T2K has the best world sensitivity for this fundamental parameter and is going to collect new data from 2023 with an upgraded detector to search for a possible discovery of symmetry violation.
T2K is a neutrino experiment designed to study the transition of neutrinos from one flavor to another as they travel (neutrino oscillations). An intense beam of muon neutrinos is generated at the J-PARC site on the east coast of Japan and directed to the SuperKamiokande neutrino detector in the mountains of western Japan. The beam is measured once before leaving the J-PARC site, using the ND280 near-field detector, and again at SuperKamiokande: the evolution of the measured intensity and the composition of the beam are used to determine the properties of the neutrinos.
The thesis work will focus on the analysis of the data for the measurement of the neutrino oscillations with new upgraded near detector installed in 2023. The objective of this new detector is to improve the performance of the ND280 near detector, to measure the neutrino interaction rate and to constrain the neutrino interaction cross sections so that the uncertainty on the number of events predicted at SuperKamiokande is reduced to about 4% (from about 8% today). The upgrade of the near detector will require to put in place a new analysis strategy to enable precise measurement of the neutrino oscillations. For the first time, the measurement of low momentum protons and neutrons produced by neutrino interactions will be exploited. Another important part of the analysis which must be updated to cope with increased statistics, is the modeling of the flux of neutrinos produced by the accelerator beamline.
A new generation of experiments is expected to multiply the data production in the next decades. In Japan, the Hyper-K experiment, and in the USA, the DUNE experiment, will be operational around 2027-2028. This thesis work will explore new analysis strategies crucial also for such next-generation experiments. If their new data confirm the preliminary results of T2K, neutrinos could well bring before ten years a key to understand the mystery of the disappearance of antimatter in our Universe.