| Neutrino physics is one of the frontiers in high energy particle physics.Neutrino oscillation is so far the only experimental evindence beyond the particle physics Standard Model(SM).A comprehensive understanding of neutrino properties is important for new physics beyond SM.Neutrino oscillation can be described by three mixing angles,two mass squared differences and a Dirac CP phase δCP.Before the Daya Bay experiment,all mixing angles except θ13 have been measured.013 is crucial in the sense that future experiments designed for δCp and mass hierarchy measurement rely heavily on the value of 013,hence completing our knowledge on neutrinos.θ13 largely determines the future direction of neutrino physics.Daya Bay Reactor Antineutrino Experiment is designed to measure θ13 precisely.Six re-actor cores(2.9 GW thermal power each)provide powerful neutrino flux.Three underground experimental halls,two near halls and one far hall,house eight antineutrino detectors in total.The mountains above the experimental halls provide overburden to shield cosmic ray induced backgrounds.The near detectors are placed several hundred meters away from the reactor cores to sample the neutrino flux from the source.The far detectors are placed at around 2 km away from the reactor cores to measured the deficit caused by θ13.A near-over-far relative measure-ment could reduce the absolute flux uncertainty,which is crucial for improving systematics and precise measurement for θ13.This thesis describes the work conducted by the author at Daya bay in three major as-pects:the hardware work on the automated calibration system;the development of data quality software and selection of good quality data;and a complete oscillation analysis with rate and spectral information.The automated calibration system is responsible for regularly calibrating the detector,im-proving the understanding of detector response and characteristics.The author participated in the work on the on-site assembly,test and installation of 24 automated calibration units on 8 antineutrino detectors.Besides,he also designed a gamma source package used in a special calibration campaign in 2012 and played a major role in the installation and data taking of the special calibration.The various calibration data allowed the relative energy scale uncertainty to below 0.2%,and absolute energy scale uncertainty to below 1%above 2 MeV.They are critical to the precise measurements of θ13 and reactor spectrum.High-quality analysis results are based on the good control of data quality.The author developed and implemented the data quality software framework,which allows the monitoring of data quality,selection of good data to provide a common and good run list to the collaboration for physics analysis.The last part is the core work of this thesis,a neutrino oscillation analysis.The author completed an entire set of work from neutrino candidates selection,evaluation of selection ef-ficiencies and systematics,estimation of residual backgrounds to the final oscillation fit.This analysis made a detailed evaluation of 9Li/8He background.It utilized 9Li-/8He-producing muon samples from data and consolidated previous evalutations of systematics by the collaboration.In addition,this analysis studied different methods to simplify the treatment of reactor fission isotope spectra and the possible improvement from a time-dependent analysis.In the end,621 calendar days’ data from Dec.24,2011 to Nov.28,2013 are analyzed.We observed 1083925 and 150684 antineutrino candidates from the near and far halls respectively.An oscillation analysis utilizing both the rate and spectral information gives the most precise measurement ofθ13 up to now,sin2 2θ13=0.083±0.005.The spectral information also allows us to give a measurement on mass squared difference in the electron antineutrino disappearance channel for the first time.△mee2=(2.50± 0.10)×10-3 eV2. |
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