TY  - THES
AU  - Singhal, Apeksha
TI  - Data analysis for solar neutrinos: final CNO measurement exploiting the directionality method with Borexino and JUNO’s potential for solar neutrino measurement
PB  - RWTH Aachen 
VL  - Dissertation
M1  - GSI-2025-01101
SP  - 201 p.
PY  - 2024
N1  - Dissertation, RWTH Aachen , 2024
AB  - This dissertation presents the recent solar neutrino measurements with the Borexino experiment and the expected sensitivity to solar neutrinos with the JUNO experiment. Solar neutrinos are created in the Sun through different fusion processes, that are classified as: the proton-proton (pp) chain and the Carbon-Nitrogen-Oxygen (CNO) cycle. The CNO cycle is a sub-dominant process in the Sun, while it is hypothesized to be the main source of energy in the heavier stars. Solar neutrinos are weakly interacting particles and thanks to their elusive nature, they are the only direct probes of the information about the solar interior. The Borexino experiment has already provided a comprehensive measurement of all pp chain neutrinos and the first detection of CNO solar neutrinos. It was a 280 t liquid scintillator (LS) detector located at the Laboratori Nazionali del Gran Sasso (LNGS) in Italy. It provided an improved measurement of CNO solar neutrinos and its implications for understanding the chemical composition of the Sun, using its latest and final data set collected in 2017-2021 period. My contributions towards the <sup>210</sup>Bi background constraint model, the production of fit inputs as well as performing the multivariate spectral fit to obtain CNO-ν rate, are presented in this thesis. These results have been published in Physical Review Letters. The first directional measurement of sub-MeV solar neutrinos in a liquid scintillator detector has also been accomplished by Borexino. A so-called Correlated and Integrated Directionality (CID) technique has been developed, which exploits the directional and sub-dominant Cherenkov information contained in the early hits of a solar neutrino event. The proof of concept of this method has been provided using <sup>7</sup>Be solar neutrinos and the results, including my contributions, are discussed in this thesis and have been published in a joint publication in Physical Review Letters and Physical Review D. The latest result from Borexino includes the directional measurement of CNO-ν solar neutrinos using CID and without the <sup>210</sup>Bi constraint for the first time. My contribution constitutes the optimisation of the fit inputs, calibration of group velocity of Cherenkov photons in the <sup>7</sup>Be-ν edge region, evaluation of the systematic uncertainties, and performing final CID fits to finally extract the CNO solar neutrinos. These results have been used to perform the combined CID and the multivariate spectral fit for the solar neutrino analysis, providing the most precise and Borexino's final CNO-ν rate, which has been published in Physical Review D. JUNO is a 20 kt LS experiment under construction in south China, with its primary goal of the determination of neutrino mass ordering. The potential of JUNO to perform <sup>7</sup>Be, pep, and CNO solar neutrino measurements with unprecedented precision is discussed in this thesis and my work includes executing the multivariate fits assuming various background contamination levels. These findings have been published in Journal of Cosmology and Astroparticle Physics. The first feasibility studies to perform the directional measurement of <sup>7</sup>Be and CNO solar neutrinos in JUNO using CID has also been explored in this thesis. I present my work regarding the CID analysis strategy and the preliminary results, which shows the improved JUNO's sensitivity to solar neutrinos.
KW  - Borexino ; JUNO ; solar neutrino ; CNO cycle ; directionality ; CNO neutrinos ; neutrino data analysis ; Toy Monte Carlo ; Bayesian ; sensitivity ; Cherenkov light (Other)
LB  - PUB:(DE-HGF)11
DO  - DOI:10.18154/RWTH-2025-01879
UR  - https://repository.gsi.de/record/362237
ER  -