SEARCH FOR NON-STANDARD NEUTRINO INTERACTIONS WITH LARGE-VOLUME LIQUID SCINTILLATOR DETECTORS

Abstract

Even though electroweak part of the Standard Model passed decades of testing and precision measurements, there is still a space for the presence of new physics. In particular, the neutrino sector in the last years has been reaching the level of precision oscillometry. However, the current data are not able to exclude many possible extended scenarios, in which new interactions comparable with the standard ones are still possible. This work is dedicated to beyond-Standard-Model interactions of neutrino and electron called Non-Standard Interactions or shortly NSI. Analogously to standard electroweak interactions, NSI could be charged current (CC) and neutral current (NC) type. Usually, in analyses of experiments, NC and CC NSI are considered separately, and I follow this strategy in the course of this work. The global search for NSI involves almost all experimental approaches of neutrino physics and goes far beyond the scope of this work. Here, instead, I look at the problem through the prism of the large-scale liquid scintillator experiments and confine the investigation to the search for NC NSI with solar neutrinos. In addition, I review CC NSI with reactor neutrinos at medium baseline. As a contribution into upcoming JUNO experiment, I investigate liquid scintillator energy response and radiopurity, which are essential for the successful realization of solar and reactor neutrino physics programs and, therefore, for NC and CC NSI search. I analyze in detail the non-linearity and energy resolution of liquid scintillator. I develop an experimental Compton coincidence technique with High Pure Germanium gamma spectrometer, provide a conservative measurement of the Birks’ ionization quenching constant kB and discuss problems related to its measurement. Throughout the study, I also formulate the optimal characteristics of the experimental apparatus for this improvement. The ultimate goal of this investigation is separating intrinsic energy resolution, which was never yet robustly measured for liquid organic scintillators. The intrinsic energy resolution may have an impact on the energy response of the new generation large liquid scintillator detectors such as JUNO and have to be carefully investigated. Applying single photon counting technique, I perform a calibration of the PMT charge scale and set apart statistical term from the total liquid scintillator energy resolution. Remaining term significantly differs from zero, indicating the presence of additional contribution associated with the intrinsic energy resolution. As an outlook, the precise estimation of the light collection should be conducted in order to ensure that its contribution is not significant to mimic the observed intrinsic resolution effect. The analysis of the radiopurity of the liquid scintillator showed that it is close to the one demanded for reactor neutrino program and CC-NSI search. Still, an improvement of purification procedure is necessary to fulfill solar neutrino program requirements for NC NSI search. Finally, I place the limits to NC…