| The neutrino oscillation phenomenon implies that the neutrino has a non-zero mass, and is a direct experimental observation of physics beyond the Standard Mod-el. Neutrino oscillations play an important role in studies searching for new physics. The mixing angleθ13in neutrino oscillation theory is of great importance for future ex-perimental studies on CP violation in the lepton sector and the neutrino mass spectrum. The Daya Bay Reactor Neutrino Experiment (Daya Bay) is a neutrino oscillation ex-periment designed to measureθ13with high precision. Electron-antineutrinos from re-actors undergo inverse beta-decay interactions in the detectors, which induce a prompt signal from the energy deposited by the positron and a delayed signal by the energy released from the neutron capture on gadolinium or hydrogen. Through the study of IBD samples tagged by neutron capture on gadolinium (nGd), Daya Bay first confirmed a nonzero value forθ13with a significance larger than5standard deviations in2012. The IBD samples tagged by neutron capture on hydrogen (nH) are independent from those by nGd, and the sample statistics can match those by nGd. The nH method is an independent approach to measureθ13.In this thesis, I first introduce the antineutrino event selections of the nH method, including muon veto, coincident pair selection, energy selections, coincidence time selection and relative distance selection. All the selection efficiencies and their uncor-related uncertainties are also fully analysed. The accidental background is the dominant background in the nH antineutrino samples. Its rate is30times larger than that in the nGd study in the far site detector. The fast neuron background spectrum is found to be different from that in the nGd study. The241Am-13C and9Li/8He background rates are also different from those in the nGd study. The predicted number of antineutrinos is estimated by the reactor neutrino spectrum and flux, baseline, detector target mass and detector efficiencies.This study analyses data from a570-day antineutrino data set taken from Decem-ber2011to November2013, including both the6AD running period and the8AD running period. About680,000and10,0000antineutrino events are observed sepa-rately in the4ADs of the near sites and4ADs of the far site. The measured number of antineutrino events in the far site is found to be6%less than the expected number predicted by the near sites. A rate-only analysis finds sin22θ13=0.072±0.011with a×2/NDF of5.2/6. The result excludes a zero value ofθ13with a significance of7.8 standard deviations.The nH analysis result can provide a precise verification of the nGd result. The precision of the nH measurement at Day a Bay is higher than the nGd measurements of the Double Chooz and RENO experiments. Moreover, the nH result will be the most preciseθ13measurement in the world for the future5to10years except for the nGd result from Daya Bay. In addition, it leads to an improved precision onθ13when combined the nGd results. Since the design of Daya Bay, the nGd method was con-servatively regarded as the only way to measureθ13. However, after investigation, it is found that the nH measurement can match the level of precision of the nGd mea-surement. The experience and method of the nH analysis on the antineutrino spectrum will be important to the future neutrino experiments, such as the future neutrino mass spectrum measurement by the JUNO experiment in China. |
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