Laser calibration and event reconstruction in Double Chooz experiment

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University of Alabama Libraries

The neutrino oscillation mixing angle θ13<\sub> was the last mixing angle that had not been determined precisely in 2006 when I started my Ph.D studies. It is exciting to witness how θ13<\sub> has evolved from a limit to a precisely measured mixing angle in a short period. The Double Chooz reactor neutrino experiment was the first to report strong evidence for a non-vanishing value of θ13<\sub> at the beginning of 2012. The latest analysis, which includes a combined “rate+shape” analysis of hydrogen and gadolinium capture inverse β–decay events, has yielded sin<\super>2<\super> 2θ13<\sub> = 0.109 ± 0.035 with only one detector running. This value is consistent with the current numbers from the Daya Bay and Reno experiments. In such a high-precision experiment, precise calibrations are crucial in reaching the ultimate sensitivity. The laser calibration system was developed by the University of Alabama group to calibrate PMT constants such as gains and time offsets, as well as measure the charge likelihoods which are used in the event energy reconstruction and supplement the time likelihoods in improving the position reconstruction accuracy. The second part of this thesis is devoted to the hardware and software development of the laser calibration system, as well as MC studies and data analyses for extracting the PMT gains, time offsets and charge likelihoods. The event reconstruction utilizes the PMT time and charge information to determine the event location and energy, which are essential parameters for all physics analyses. A good understanding of the detector response significantly reduces the detector related systematic errors and improves the sensitivity, especially in the two detector phase, where the dominant uncertainties from the reactor flux mostly cancel out. The third part of this thesis is dedicated to the reconstruction algorithm developed by our group, position accuracy studies and energy reconstruction studies, which aims towards fully understanding the detector response.

Electronic Thesis or Dissertation
Particle physics