ATMOSPHERIC NEUTRINO SPECTRUM RECONSTRUCTION WITH THE JUNO EXPERIMENT

Abstract

The atmospheric neutrino flux represents a continuous source that can be exploited to infer properties about Cosmic Rays and neutrino oscillation physics. The extremely low neutrino cross section allows to preserve the original information at the production and to release it inside a detector wi thout being modified by deflection, nor absorption. Atmospheric neutrinos represent also an important source of background for rare event searches in the multi-MeV energy range, where current flux predictions have large uncertainties. The JUNO observatory, a 20 kt liquid scintillator currently under construc tion in China, will be able to detect atmospheric neutrinos, given the large fiducial volume and the excellent energy resolution. The light produced in neutrino interactions will be collected by a double-system of photosensors: about 18.000 20” PMTs and about 25.000 3” PMTs. The rock overburden above the experimental hall is around 700 m and the experiment is expected to complete construction in 2021. In this thesis, the JUNO potential in reconstructing the atmospheric neu trino spectrum has been evaluated. A large set of Monte Carlo events has been used to simulate the performances of the detector, from neutrino inte ractions generation to the detector response. About 5 years of data-taking has also been simulated, in order to understand the detector potential on a reasonable time-scale. A discrimination algorithm has been developed to separate the flavor of primary neutrinos, exploiting the different time evo lution of scintillation light on PMTs. A probabilistic unfolding method has been used, in order to infer the primary neutrino energy spectrum by loo king at the detector output. The simulated spectrum has been reconstructed between 100 MeV and 10 GeV, showing a great potential of the detector in the atmospheric low energy region. The uncertainties on the final flux, in cluding both statistic and the systematic contributions, range between 10% and 25%, with the best performances obtained at the GeV. The final result shows the possibility of JUNO to add information in the low-energy region, which can represent a further input to constrain theoretical flux predictions